(** The checker: AST → typed IR. Two passes, because top-level names in a package are order-independent (plan.org, Modules): the first collects every type, signature and global, the second checks bodies against them. Mutually recursive functions need no forward declaration, and a struct may be used above where it is declared. Checking is *bidirectional*. An expression is checked against an expected type when there is one and inferred when there is not, which is what makes [None], a bare [0] and a struct literal work without any inference engine: the expected type flows in from the function's return type, the parameter it is being passed to, or the field it is being stored in. The rule from the two misparse bugs applies here too: *anything not yet implemented is rejected by name*, never approximated. Milestone 2 is calc-me.flan and nothing more (plan.org, Build sequence), so [Vec], [Map], [Result]/[try], user data types, closures, [dotimes], [defer], generics and cross-package imports are all errors with a message that says which milestone they belong to. *) let fail = Loc.fail (* [List.map]'s evaluation order is unspecified, and checking allocates frame slots as a side effect. Left-to-right is required, not a preference: a later let binding sees an earlier one, and slot numbering must be reproducible. *) let rec map_lr f = function | [] -> [] | x :: rest -> let y = f x in y :: map_lr f rest let rec map2_lr f xs ys = match xs, ys with | [], [] -> [] | x :: xs, y :: ys -> let z = f x y in z :: map2_lr f xs ys | _ -> invalid_arg "map2_lr" (* ── Environments ──────────────────────────────────────────────────── *) type binding = { slot : int; bty : Types.t; assignable : bool; (* locals are places; parameters are not — spec-memory *) } type env = { structs : (string, Tast.structure) Hashtbl.t; datas : (string, Tast.data) Hashtbl.t; (* The untagged unions, by name, and they are [Tast.structure] values on purpose: a union's members *are* a field list, and every one of them is at offset zero. Giving them a record of their own would have meant a second shape for [field_index] and for every walk over a member list, to say nothing new — which table the name is in is already what says whether the offsets are cumulative or all zero, exactly as it is for a data type. *) unions : (string, Tast.structure) Hashtbl.t; (* Every data type case, twice over: once under its full spelling ["U.C"], which is how a value of it is written, and once under the bare ["C"], which is how a [match] arm names it and how a mistake spells a constructor. The full spelling is a key rather than something split out of a dotted name at the use site, because a data type's own name can contain a slash (an imported [rl/U]) and may one day contain a dot; string surgery would own an edge this does not have to. The bare entry is deliberately last-writer-wins and is *only* used to say "C is a case of U, write (U.C ...)". Two data types may share a case name — construction is qualified and a pattern resolves against the scrutinee, so both are unambiguous — and refusing that would be a restriction with no mechanism behind it. *) cases : (string, string * Tast.variant) Hashtbl.t; aliases : (string, Ast.texpr) Hashtbl.t; consts : (string, int64) Hashtbl.t; (* compile-time array lengths *) locs : (string, Loc.t) Hashtbl.t; (* where each type was declared *) (* Enum name -> its members, in declaration order. A keyword at a call site resolves against this and nothing else. *) enums : (string, (string * int64) list) Hashtbl.t; (* Flan name -> the C symbol it is really called by. A foreign function is an ordinary entry in [fns] as well; this only records how to name it. *) externs : (string, string) Hashtbl.t; fns : (string, Types.t list * Types.t) Hashtbl.t; globals : (string, Types.t * bool) Hashtbl.t; (* type, is a constant *) (* Functions the checker made up: a handler-bind clause is lifted into one, because a handler is called from wherever the signal was and cannot be a branch in the function that established it. *) mutable lifted : Tast.fn list; (* ── Generics by monomorphisation (spike, milestone 5) ──────────────── A generic [defn] is *not* in [fns]: its signature mentions type variables and nothing can be called at it. It lives here, as the AST it was written as, and every call site turns it into an ordinary function with concrete types. Odin's model exactly — [find_or_generate_polymorphic_procedure] keeps the source [Entity] and hangs generated ones off it. *) generics : (string, Ast.fn) Hashtbl.t; (* Its signature as *written*: parameter and return types with [Types.Var] in them. This is the pattern a call site matches its argument types against to bind the variables. *) gsigs : (string, string list * Types.t list * Types.t) Hashtbl.t; (* The instantiation cache. Odin's [gen_procs] list, keyed the way Odin keys it: a linear scan comparing whole concrete signatures with [are_types_identical] — here [Types.equal] pairwise. Same types twice means one copy. *) insts : (string, (Types.t list * Types.t * string) list ref) Hashtbl.t; (* The copies themselves, in the order they were generated. They are ordinary [Tast.fn]s from here down; nothing in a backend knows they were ever generic. *) mutable instances : Tast.fn list; (* The type variables in scope while a generic signature is being resolved. Empty everywhere else, which is what keeps the lowercase rejection at [resolve_name] the default. *) mutable tyvars : string list; (* What each of them is bound to while one instantiation's body is checked. [resolve_name] consults it before anything else, so the body resolves [t] to [i32] and every node under it is concrete. *) mutable subst : (string * Types.t) list; (* The [where] predicates in scope: what the abstract pass may assume about the variables, and what each instantiation checks its concrete types answer yes to. Empty everywhere a generic signature or body is not being resolved, which is what keeps every refusal below the default. *) mutable tvpreds : Ast.pred list; (* The chain of instantiations currently being generated, innermost last: the generic's name and the concrete parameter types each copy was asked for. It is the refusal for a generic that instantiates itself without end — [(defn grow [x $t] () (grow [x x]))] asks for a copy at [[2 t]], which asks for one at [[2 [2 t]]], forever — and without it the checker does not fail, it *hangs*, which through [Session.eval] is [C-c C-c] hanging with the dev daemon wedged behind it. The test is structural rather than a depth count. A depth count names a number the programmer did not write and cannot act on; this names the chain. Odin has no cap of its own to copy, so there was nothing to borrow. *) mutable chain : (string * Types.t list * Loc.t) list; } let new_env () = { structs = Hashtbl.create 16; datas = Hashtbl.create 16; unions = Hashtbl.create 16; cases = Hashtbl.create 32; aliases = Hashtbl.create 16; consts = Hashtbl.create 16; locs = Hashtbl.create 16; enums = Hashtbl.create 8; externs = Hashtbl.create 32; fns = Hashtbl.create 32; globals = Hashtbl.create 16; lifted = []; generics = Hashtbl.create 8; gsigs = Hashtbl.create 8; insts = Hashtbl.create 8; instances = []; tyvars = []; subst = []; tvpreds = []; chain = []; } (* Where a named type was declared, and what it has, as a note. This is the second half of the two-place messages: a refusal that says [Cursor has no field pos] is true, and the reader's next move is always to go and look at Cursor. Attaching the declaration's location and its actual field names means the answer arrives with the question, and [next-error] will take you there because a note prints as an entry of its own. Empty when the name is not one this environment placed, so it degrades to the message alone rather than to a wrong pointer. *) let declared_note env name = match Hashtbl.find_opt env.locs name with | None -> [] | Some at -> let names = match Hashtbl.find_opt env.structs name with | Some s -> List.map (fun (f : Tast.field) -> f.Tast.fname) s.Tast.fields | None -> (match Hashtbl.find_opt env.datas name with | Some u -> List.map (fun (c : Tast.variant) -> c.Tast.vname) u.Tast.cases | None -> match Hashtbl.find_opt env.unions name with | Some u -> List.map (fun (f : Tast.field) -> f.Tast.fname) u.Tast.fields | None -> []) in let what = if names = [] then name ^ " is declared here" else name ^ " is declared here, with " ^ String.concat ", " names in [ Loc.note at what ] (* What a [break] or a [continue] may be talking about, innermost first. [Lloop] is a loop it is lexically inside, carrying its label if it was given one. [Lbarrier] is something a jump may not cross, named so the refusal can say which — and the barriers are the whole of the answer to the question [return]'s [in_frames] rule could not answer. [return] is refused inside a [handler-bind] or a [restart-case] blanketly, because a return *always* crosses the frames established there and leaves them on the stack pointing into a frame that has gone. A break crosses only sometimes: a loop written wholly inside a [restart-case] body has a perfectly good local break, and refusing it would be refusing the common case for the uncommon one. So the rule here is relative rather than blanket — a jump is refused exactly when a barrier stands between it and the loop it names — and the two rules agree on the case they share, because a [return] is a jump whose target is always outside every barrier. A [defer]'s forms are a barrier for a different reason with the same shape: they are copied into the function's exit paths, where the loop they were written next to no longer exists. A loop *inside* the defer is fine, which is again the relative rule and not a blanket one. A handler clause is not on this list at all: it is lifted into a function of its own and gets a fresh [ctx], so its loops start empty and nothing inside it can name a loop outside it. *) type lentry = | Lloop of string option (* A [(loop ...)], carrying the slot and type of each of its names so that a [recur] can rebind them. It is *also* a barrier for [break] and [continue]: a loop answers with the value of its body, so a jump that left one would have no value to give. A [while] written inside a loop is unaffected, which is the relative rule doing its job again. *) | Lrecur of (int * Types.t) list | Lbarrier of string (* Per-function state. Slots are never reused, so [slots] is also the frame size — the interpreter allocates one array of this length per call. *) type ctx = { env : env; ret : Types.t; mutable slots : int; (* The type of each slot, newest first. A backend needs it to size the frame — nothing else records it, since the IR refers to slots by index. *) mutable slot_tys : Types.t list; (* The source name of each slot, newest first, parallel to [slot_tys]. [None] for a slot the checker invented -- see [Tast.fn.snames]. Recorded here rather than recovered later because this scope list is the only place that ever knows it. *) mutable slot_names : string option list; mutable scope : (string * binding) list; (* innermost first *) (* Deferred forms, most recently registered first — which is also the order they run in. [defer] is function-scoped, so this list belongs to the function and not to a block — see [defer_ok] for where one may be written and [check_fn] for where the list is spliced onto the exit paths. *) mutable defers : Tast.expr list; (* Where a [defer] may be written, which is exactly: a form whose extent is the whole function body. Two things have that extent and only two — a top-level form of the body, and a form in the body of a [let] that itself has it, to any depth. A [let] always registers and its bindings outlive the block textually enclosing them, because a [let] is not a frame here: its bindings are function slots like any other, and nothing is released at scope exit (spec-memory.md, "When storage is released"). Everything else is refused, and the two that matter are refused for a reason rather than by omission. [defer] is a *compile-time* construct — the cleanup is copied into every exit path — so a branch would have to express "maybe registered", which it cannot, and a loop body would fire once at function exit rather than once per iteration. The flag is set immediately before each form that may carry one, never once around a body: [check] clears it on entry, so a body whose first form set it would otherwise refuse the second. [defer_block] names the innermost construct that cleared it, so the refusal says which. *) mutable defer_ok : bool; mutable defer_block : string; (* Only for the two things a handler clause cannot do. [outer] is the establishing function's scope, kept so that a reference to one of its locals can be refused for the reason it is really refused for rather than as an unknown name. *) outer : (string * binding) list; (* Set on the context of a body the checker lifted into a function of its own — a handler clause, or an [fn] literal — and naming which, so the refusal below says why the enclosing function's locals are not there. Both are the same gap: capture does not exist. *) mutable outer_what : string option; (* True wherever handler or restart frames established by this function are on the stack. A [return] from there would leave them pointing into a frame that has gone, so it is refused — the same rule as [defer] inside a block. *) mutable in_frames : string option; (* The loops and the barriers this form is inside, innermost first. See [lentry]: it is what [break] and [continue] resolve against, and the whole of why they are not a goto — a label that names no loop on this list is refused, so control can only leave a loop it is already in. *) mutable loops : lentry list; (* True where this form's value is the value of the enclosing [loop]'s body, which is the only place a [recur] may stand. Read and withdrawn at the top of [check] exactly as [defer_ok] is, and granted again by the three forms that pass a tail through: the last form of a block, both arms of an [if], and a [match] arm. Everything else is therefore non-tail by construction, and no walk has to enumerate the cases that are not. *) mutable tail : bool; (* True inside a [defer]'s forms. A defer is the cleanup a transfer runs on its way out (§5), so a transfer *starting* there has no answer: this function's defers are already half run and the first transfer's target is already in hand. Refused where it is written. *) mutable in_defer : bool; (* Move tracking, spec-memory.md's "(Vec T) and (Map K V) are move-only". [dead] is the slots whose value has been moved out, with where it went, so that a second use names the first rather than reporting a type error about nothing. It is flow-sensitive at an [if]: the two arms are checked from the same starting set and the *data type* survives the join, so moving in one arm only is still a move afterwards — and moving in both arms, which is legal, is not two errors. [borrow] is set only while checking the *target* of an operation that reads a container without consuming it ([at], [len], [as-slice], [push], [reserve], [clone]). Without it every one of those would look like a move and no program could push twice. *) mutable dead : (int * Loc.t) list; mutable borrow : bool; (* The function being checked, so a clause lifted out of it can be named after it. The name has to be stable and has to say whose it is: a redefinition module emits the clauses belonging to the bodies it is replacing, and nothing else in the program can tell it which those are. *) owner : string; } (* [?name] is the source name, when there is one. It is optional so that the several places that allocate a hidden slot say nothing and get [None] -- a synthesized slot cannot accidentally acquire a name it was never given. *) let fresh_slot ?name ctx ty = let s = ctx.slots in ctx.slots <- s + 1; ctx.slot_tys <- ty :: ctx.slot_tys; ctx.slot_names <- name :: ctx.slot_names; s (* Shadowing is legal -- [(let [v 11] (let [v 22] ...))] is two slots, both named [v] -- and the debug info has nowhere to put the distinction. Every [!DILocalVariable] is scoped to the subprogram, because the typed IR has no block structure for a [!DILexicalBlock] to be built from, so two variables called [v] land in one flat scope and lldb answers [p v] with whichever it finds first. Measured, not assumed: it answers with the *outer* one, so it prints 11 while the body it is stopped in is computing with 22, and the inner binding is not listed at all. That is the one outcome worse than printing [s3]: a name the debugger is confident about and wrong about. So a repeat of a name already bound in this function gets a suffix, and both bindings are then visible and unambiguous. [~] is the reader's delimiter and cannot occur in a source symbol (the same reason [destructure~nth] is spelled that way), so [v~2] is visibly the compiler's doing and can never collide with something the programmer wrote. This is a way of not lying, not a way of being right: [v] is still the outer binding everywhere, including inside the inner one's extent. Scoping the variables properly means emitting a [!DILexicalBlock] per [Let] and moving the [llvm.dbg.declare]s out of the entry block to the binding sites, which needs block structure this IR does not carry. *) let bind ctx name bty ~assignable = let taken n = List.exists (fun s -> s = Some n) ctx.slot_names in let name' = if not (taken name) then name else let rec go k = let c = Printf.sprintf "%s~%d" name k in if taken c then go (k + 1) else c in go 2 in let slot = fresh_slot ~name:name' ctx bty in (* [ctx.scope] keeps the *source* name: the suffix is a debug-info artifact and resolving [v] must still find the innermost binding. *) ctx.scope <- (name, { slot; bty; assignable }) :: ctx.scope; slot let lookup ctx name = List.assoc_opt name ctx.scope (* A handler clause is lifted into a function of its own, so the establishing function's locals are simply not there. Capturing them is a closure with an explicit environment — spec-memory.md's case 2, a non-escaping [fn] capturing by value into a stack environment, since a handler frame does not outlive the function that pushed it — and until that exists a reference to one is refused for the reason it is really refused for, rather than as a name nobody has heard of. *) let captured ctx loc name = match ctx.outer_what with | Some what when List.mem_assoc name ctx.outer -> let why = if String.equal what "a handler" then "a handler runs from wherever the signal was. Use a global, or pass \ it on the condition" else "an fn is lifted into a function of its own and is handed nothing but \ its parameters. Pass it in, or use a global" in Loc.failk "check/capture" loc "%s cannot see %s: it is a local of the enclosing function, and %s." what name why | _ -> () let scoped ctx f = let saved = ctx.scope in let r = f () in ctx.scope <- saved; r (* A scope that is also a named blocker for [defer]. An arm of an [if] or a [match] runs only sometimes, and "maybe registered" is not something a compile-time construct can express — the cleanup is copied into every exit path or into none — so the refusal is about the branch and says so. Outside the [check] recursion on purpose: inside it the inferred type would be monomorphic, and the two callers pass functions returning different things. *) let branch ctx f = let blocker = ctx.defer_block in ctx.defer_block <- "a branch"; let r = scoped ctx f in ctx.defer_block <- blocker; r (* ── Type resolution ───────────────────────────────────────────────── *) let unimplemented loc what milestone = fail loc "%s is not implemented yet — milestone %d (see plan.org)" what milestone (* ── where predicates ────────────────────────────────────────────────── A predicate is a compile-time question about a type, and that is the whole of it. It carries no implementation, selects no instance, and is not extensible: it gates a builtin the compiler already has. So there are no dictionaries, no coherence rules and no run-time cost — and the ceiling is that nobody can supply a [<] of their own, which does not bind because every operation the prelude and the containers need is a primitive. Odin's [where] clause is the same shape ([core/slice/slice.odin:289] is [where intrinsics.type_is_ordered(T)]) with forty-one predicates against these five. The fifth, [copyable?], has no Odin counterpart at all: Odin has no move semantics, so [$T] never has to answer the question. The prior art there is Rust's [T: Copy], with the difference that [copyable?] is a question the compiler answers rather than a trait a user implements. *) let predicate_names = [ "ordered?"; "equal?"; "hashable?"; "numeric?"; "copyable?" ] (* ── What a type owns, transitively ──────────────────────────────────── spec-memory.md: "Ownership is structural, not declared." [Types.is_move_only] answers the same question one level deep and deliberately stops there — a [Named] is not move-only, because making it so is the transitive ownership model that recursive teardown would need, and there is no recursive teardown. This walk is the *other* use of the same fact, and the two must not be collapsed: nothing here feeds the move checker, and a type this says yes about is still copied and still tracked exactly as it was yesterday. What it decides, and the only thing it decides, is whether a container of this element type has to be built against a region allocator — see [region_only] below and [flan_alloc_region_only] in the runtime. That is a question about *release*, so it is asked of every arm a release would have to reach and would not: a Vec, Map or Pool owns a block outright; an Option, a fixed array, a struct or a data type's case owns whatever its payload does. It does not live in [Types] for the reason [Types.keyable] gives: that module has no field table. The [seen] list is the cycle guard, and the cycle is real — the recursive dynamic value this exists for holds a [(Vec Value)], so [Value]'s walk reaches [Value]. Answering [false] for a name already on the path is right rather than merely terminating: whatever made the outer name own something was found by the arm that got here, and a name cannot contain itself by value anyway — [check_finite] refuses that — only through a container, which is an arm that answers for itself. [env.unions], the untagged ones, are deliberately not consulted: a move-only member in one is refused outright, and that refusal is not waiting on teardown the way these were — nothing anywhere records which member is live, so there is no fact a release could read. A region removes the teardown question and leaves that one exactly where it was, so an untagged union owns nothing and there is nothing here to walk. *) let owning_fields env n = match Hashtbl.find_opt env.structs n with | Some s -> [ s.Tast.fields ] | None -> match Hashtbl.find_opt env.datas n with | Some d -> List.map (fun (c : Tast.variant) -> c.Tast.vfields) d.Tast.cases | None -> [] let rec owning env ?(seen = []) (t : Types.t) = match t with | Types.Vec _ | Types.Map _ | Types.Pool _ -> true | Types.Option e | Types.Array (_, e) -> owning env ~seen e | Types.Named n -> not (List.mem n seen) && List.exists (List.exists (fun (f : Tast.field) -> owning env ~seen:(n :: seen) f.Tast.fty)) (owning_fields env n) | _ -> false (* Does a container of this type have to be built against an allocator that cannot free one block? Only the half a release would have to walk is asked: a map's key cannot own anything — [map_type] refuses one, because a key that owned storage would hash its header rather than what it points at — so the value is the whole of the question there. *) let region_only env (t : Types.t) = match t with | Types.Vec e | Types.Pool e -> owning env e | Types.Map (_, v) -> owning env v | _ -> false (* Does a concrete type answer yes? Checked at every instantiation, against the type the call site asked for. *) let pred_holds p (t : Types.t) = match p with | "ordered?" -> Types.is_comparable t | "equal?" -> Types.is_equatable t (* [Types.keyable] says yes to a struct and leaves its fields to [key_pair], which walks them at the operation. That split is the existing one and is kept: a generic declared [hashable?] and instantiated at a struct whose fields are not keyable is refused where every other program is, by [key_pair]. *) | "hashable?" -> Types.keyable t | "numeric?" -> Types.is_numeric t | "copyable?" -> not (Types.is_move_only t) | _ -> false (* What one declared predicate *also* gives you. These are entailments over the type system as it stands, not conveniences: every type [is_comparable] admits is a number or an enum, so it is equatable and it is not move-only. The table is only sound while that is true — an ordered move-only type, or an ordered type with no [=], would make it wrong — so it lives in one place and says so. The gain is real ergonomics: [{:where (ordered? $t)}] is enough for a [sort!] that also compares and reads its elements twice, rather than three predicates on one line. *) let pred_entails ~declared ~wanted = String.equal declared wanted || match wanted, declared with | "ordered?", "numeric?" -> true | "equal?", ("numeric?" | "ordered?") -> true | "copyable?", ("numeric?" | "ordered?" | "equal?" | "hashable?") -> true | _ -> false let declares preds v wanted = List.exists (fun (p : Ast.pred) -> String.equal p.Ast.pvar v && pred_entails ~declared:p.Ast.pname ~wanted) preds (* Which variable, if any, a type bottoms out at. Only a bare variable can carry a predicate: [(Vec t)] is a Vec whatever [t] is, and its own properties are the Vec's. *) let tyvar_of (t : Types.t) = match t with Types.Var v -> Some v | _ -> None (* ── Move-only, with a type variable defaulting to move ──────────────── [Types.is_move_only (Var _)] is [false] and cannot be anything else: the same variable is [i32] at one instantiation and [(Vec i32)] at the next, so the property is not decidable abstractly. The author's decision is to default to **move**, because move is the *stricter* rule: assuming it can only refuse a program that would have been fine, never admit one that double-frees. [copyable?] is the opt-out, exactly as Rust's [T: Copy] is. In the body this means a generic may not use a parameter twice without declaring [copyable?]: [(defn twice [x $t] $t (+ x x))] is refused, which is right — correct at [i32], a double read of a moved value at [(Vec i32)], and the checker cannot tell which until it substitutes. A [Var] only ever survives the abstract pass. Inside an instantiation [env.subst] has made everything concrete, so this is [Types.is_move_only] there and the strictness costs nothing at a call site. *) let rec move_only preds (t : Types.t) = match t with | Types.Var v -> not (declares preds v "copyable?") | Types.Option e | Types.Array (_, e) -> move_only preds e | t -> Types.is_move_only t (* ── (Map K V), spec-memory.md ────────────────────────────────────────── Both halves are checked where the type is written, not where an operation is, so that a map nothing ever uses is still refused if it cannot work. [Check.key_pair] emits the hash and equality pair later, at the operation, and repeats these refusals rather than assuming: the two are reached by different paths and a silent disagreement between them would be worse than saying the same thing twice. *) let map_type ?(preds = []) loc (k : Types.t) (v : Types.t) = ignore preds; (* The value used to be refused here when it owned anything, in the same words [(Vec (Vec T))] used, and the refusal is gone for the reason set out over [map-new]: it was about *teardown*, and which tier this map will be built against is not knowable where its type is written. The question is asked at the construction instead, of the allocator, once. *) (* () has no bytes, so a slot for one is a slot of nothing: the cell geometry divides the cache line by the element size and there is nothing to divide by. It is also the natural spelling of a *set*, which is why someone will write it, so it is refused by name rather than by a crash. *) if Types.equal v Types.Unit then fail loc "a map value cannot be () — there is nothing to store. A set of keys \ is not built yet; use (Map %s bool) and ignore the value" (Types.to_string k); if Types.equal k Types.Unit then fail loc "a map key cannot be () — every key would be the same key"; (* The key, as far as the type alone can say. A struct passes here and is decided at the operation, by [key_pair], which walks its fields — the struct table is not necessarily complete while a type is being resolved, and every map that exists reaches an operation anyway, because a global of move-only type is refused and a local needs (map-new). *) (* A type variable is a map key exactly when the [where] clause says it is hashable. Nothing else about it is knowable here, and falling through to [Types.keyable] would answer no for a variable that is about to be instantiated at [string]. *) if not (match k with | Types.Var v -> declares preds v "hashable?" | k -> Types.keyable k) then fail loc "%s is not a map key. The first implementation takes integers, enums, \ bools, strings, fixed arrays of those, and value structs composed of \ those (spec-memory.md, \"Maps — first implementation\"). A float has \ no usable equality — NaN is not equal to itself — and a Ptr, a slice, \ a Vec or a Map would hash an address rather than what it points at" (Types.to_string k); Types.Map (k, v) (* The positions a function value may not be written in, and the one reason they are all the same position: something zeroes it. ZII is the language's rule — an omitted struct field, a fixed array's elements, a [defvar] with no initialiser are all all-bytes-zero — and a zeroed function value is a null pointer with a signature on it, which is the one kind of zero that cannot be used for anything. Every other type's zero is a value: 0, false, an empty slice, [None], a data type's first case. So these are refused where they are written rather than left to crash at the call. A parameter, a return type, a [let] binding and an [(Option (Fn ...))] are not on the list: none of them is ever conjured, and an [Option]'s zero is a [None] whose tag nobody may look past. *) let rec no_zeroed_fn loc what (t : Types.t) = match t with | Types.Fn _ -> fail loc "%s cannot be %s: it would be zeroed, and a zeroed function value is \ a null pointer — every other type's zero is a value it can have, and \ this one is not. Pass it as a parameter, or hold it in a let" what (Types.to_string t) | Types.Array (_, e) -> no_zeroed_fn loc what e | _ -> () let rec resolve env ?(seen = []) (t : Ast.texpr) : Types.t = let loc = t.Ast.tloc in match t.Ast.t with | Ast.Tname n -> resolve_name env ~seen loc n | Ast.Tslice e -> Types.Slice (resolve env ~seen e) | Ast.Tarray (l, e) -> let e = resolve env ~seen e in no_zeroed_fn loc "a fixed array's element" e; Types.Array (array_len env loc l, e) (* {K V} is the type spelling. There is no map *literal*: a bare map form in expression position is a struct literal's field list, and giving the same braces two meanings is what the colon-to-dot change was for. A map is built with (map-new) and filled with (put). *) | Ast.Tmap (k, v) -> map_type ~preds:env.tvpreds loc (resolve env ~seen k) (resolve env ~seen v) (* (Fn [T ...] R): a function value, which is one code address and no environment beside it. There is no capture — [check_fn] refuses a reference to an enclosing local by name — so this is a pointer with a signature and nothing about it can dangle. Where one may be *written* is narrower than where the type resolves, and the two rules live apart on purpose: this is what the spelling means, and [no_zeroed_fn] is where a position that would zero one is refused. A parameter, a return type and a let binding are the positions that work. *) | Ast.Tfn (ps, r) -> Types.Fn (List.map (resolve env ~seen) ps, resolve env ~seen r) | Ast.Tapp (name, args) -> (match name, args with | "Ptr", [ a ] -> Types.Ptr (resolve env ~seen a) | "Option", [ a ] -> Types.Option (resolve env ~seen a) | ("Ptr" | "Option"), _ -> fail loc "(%s T) takes exactly one type" name | "Vec", [ a ] -> let e = resolve env ~seen a in (* A Vec of a Vec used to be refused here, and the refusal named two different failures under one sentence: that [clone] would duplicate inner headers instead of copying, and that [free] would drop their buffers on the floor. Only the second one was about *teardown*, and only the second one an arena answers — [free-all] takes the region and the inner blocks with it, because they came out of the same region. So the type is admitted, the tier is checked at the construction where the allocator is a value that exists (see [vec-new]), and [clone] stays refused at the operation, on its own merits, in its own words. It cannot be refused *here* because nothing here knows the tier: [with-allocator] rebinds a dynamic variable, so which allocator a [(vec-new)] meets is not a property of where the type is written. *) Types.Vec e | "Vec", _ -> fail loc "(Vec T) takes exactly one type" | "Map", [ k; v ] -> map_type ~preds:env.tvpreds loc (resolve env ~seen k) (resolve env ~seen v) | "Map", _ -> fail loc "(Map K V) takes exactly two types" | "Result", _ -> unimplemented loc "(Result T E)" 6 | "Pool", [ a ] -> let e = resolve env ~seen a in (* Lifted with the Vec's and pushed to the construction with it, and a pool is the one of the three where that is not quite the same trade, because a pool has a release point a Vec does not: [(release p h)] recycles one slot while the pool lives on. In a region that costs a block that stays allocated until [free-all] and is never handed back — the slot itself is reused, since the next insert overwrites those bytes, but whatever the dead element pointed at is stranded. That is a region leak bounded by the region, which is the bargain a region already is: an arena's whole proposition is that nothing comes back before the reset. It is not the unbounded leak the heap would take, and it is not a use-after-free — nothing is released twice because nothing is released once. Said here rather than left for a reader to work out, because "reuse" is the word that makes a pool look different from a Vec and it deserves an answer. *) Types.Pool e | "Pool", _ -> fail loc "(Pool T) takes exactly one type" | "Handle", [ a ] -> Types.Handle (resolve env ~seen a) | "Handle", _ -> fail loc "(Handle T) takes exactly one type" | _ -> fail loc "%s takes no type arguments — generics are milestone 5" name) (* One edit away from a type that exists — a substitution, an insertion, a deletion or a transposition of neighbours. Bounded at one, because two edits is no longer a typo, it is a guess. *) and near_miss env n = let one_edit a b = let la = String.length a and lb = String.length b in if abs (la - lb) > 1 then false else begin (* Walk both until they diverge, then require the tails to match with the single edit applied. *) let i = ref 0 in while !i < la && !i < lb && a.[!i] = b.[!i] do incr i done; let ta s k = String.sub s k (String.length s - k) in if la = lb then !i < la && (ta a (!i + 1) = ta b (!i + 1) (* stirng/string: two neighbours swapped. *) || (!i + 1 < la && a.[!i] = b.[!i + 1] && a.[!i + 1] = b.[!i] && ta a (!i + 2) = ta b (!i + 2))) else if la < lb then ta a !i = ta b (!i + 1) else ta a (!i + 1) = ta b !i end in let candidates = Types.primitive_names @ Hashtbl.fold (fun k _ acc -> k :: acc) env.aliases [] @ Hashtbl.fold (fun k _ acc -> k :: acc) env.structs [] @ Hashtbl.fold (fun k _ acc -> k :: acc) env.datas [] @ Hashtbl.fold (fun k _ acc -> k :: acc) env.unions [] @ Hashtbl.fold (fun k _ acc -> k :: acc) env.enums [] in List.find_opt (fun c -> c <> n && one_edit n c) candidates and resolve_name env ~seen loc n = (* ── Type variables, with a sigil at the binding site ───────────────── [$t] *introduces* a variable and bare [t] uses it, which is Odin's spelling ([$T] in the signature, [T] in the body). The sigil is read as an ordinary symbol character, so the whole decision lives here: nothing in the reader, the parser or the AST knows the character means anything. Which names are variables is decided before this is ever called — [signature_tyvars] scans the signature for the sigil and puts the bare names in [env.tyvars] — so an unknown lowercase name is still the unknown-type error it always was. That is the point of the sigil: without one, a mistyped type name silently became a type parameter and made the function more permissive than it was written to be. *) let bare = if n <> "" && n.[0] = '$' then String.sub n 1 (String.length n - 1) else n in match List.assoc_opt bare env.subst with (* Inside an instantiation: the variable is this concrete type, and every node checked under it is as concrete as if it had been written out. *) | Some t -> t | None -> if List.mem bare env.tyvars then Types.Var bare else if n <> bare then (* A sigil somewhere that is not a [defn] signature: a struct field, a global, a [let] annotation. There is nowhere for it to bind, so it is the error rather than a variable with no scope. *) Loc.failk "check/unbound-type-variable" loc "%s introduces a type variable, and only a defn signature can — write \ the concrete type here" n else match Types.ikind_of_name n with | Some k -> Types.Int k | None -> match Types.fkind_of_name n with | Some k -> Types.Float k | None -> match n with | "bool" -> Types.Bool | "string" -> Types.String | "Unit" -> Types.Unit | "Never" -> Types.Never (* A builtin opaque type, the way [string] is a builtin ptr+len. There is no user-writable constructor and no way to name its procedure: see Types, and NEXT.md's "the escape is real". *) | "Allocator" -> Types.Alloc | _ when Hashtbl.mem env.aliases n -> if List.mem n seen then fail loc "the type alias %s is defined in terms of itself" n else resolve env ~seen:(n :: seen) (Hashtbl.find env.aliases n) | _ when Hashtbl.mem env.structs n -> Types.Named n (* A data type is [Named] exactly as a struct is: one case in [Types.t] covers both, and which table the name is in is what tells them apart. Keeping them one case is what lets a data type be a field, a parameter, a return type and a slot without a single one of those paths learning that data types exist. *) | _ when Hashtbl.mem env.datas n -> Types.Named n (* And so is an untagged union, for the same reason: it is a value of a size and an alignment, and nothing that carries one has to know it is a union rather than a struct. *) | _ when Hashtbl.mem env.unions n -> Types.Named n | _ when Hashtbl.mem env.enums n -> Types.Enum n (* A typo in a primitive is lowercase too, and the type-variable rule below would otherwise report [f65] as unimplemented generics and send you to plan.org instead of to the character you mistyped. *) | _ when near_miss env n <> None -> Loc.failk "check/unknown-type" loc "unknown type %s — did you mean %s?" n (Option.get (near_miss env n)) (* Lowercase is a type variable, Capitalized is concrete — no sigil (plan.org, Types). A variable parses, but nothing at milestone 2 can give a value one, so it is rejected here rather than later. *) | _ when n <> "" && n.[0] = Char.lowercase_ascii n.[0] -> unimplemented loc (Printf.sprintf "generic code over the type variable %s" n) 5 | _ -> Loc.failk "check/unknown-type" loc "unknown type %s" n and array_len env loc = function | Ast.Lint n -> n | Ast.Lname n -> (match Hashtbl.find_opt env.consts n with | Some v -> v | None -> fail loc "%s is not a compile-time integer constant, so it cannot be \ an array length" n) (* ── Generics: the four operations monomorphisation needs ─────────────── Naming a variable, binding one from an argument, substituting the binding back in, and spelling the result as a symbol. Everything else about the feature is where these are called from. *) (* The variables a signature introduces: every [$t] written in it, in the order written, once each. Only a [defn] signature is scanned, which is what makes the binding site a *place* and not merely a spelling. *) let signature_tyvars (fn : Ast.fn) = let acc = ref [] in let name loc n = if n <> "" && n.[0] = '$' then begin let bare = String.sub n 1 (String.length n - 1) in if bare = "" then fail loc "$ on its own does not name a type variable"; (* [$i32] would shadow a machine type inside the body and read as one everywhere else. There is no reason to want it. *) if List.mem bare Types.primitive_names || Types.ikind_of_name bare <> None || Types.fkind_of_name bare <> None then fail loc "%s is a type, so $%s cannot be a type variable" bare bare; if not (List.mem bare !acc) then acc := bare :: !acc end in let rec ty (t : Ast.texpr) = match t.Ast.t with | Ast.Tname n -> name t.Ast.tloc n | Ast.Tslice e -> ty e | Ast.Tarray (_, e) -> ty e | Ast.Tmap (k, v) -> ty k; ty v (* The head of an application is a constructor — [Ptr], [Option], [Vec] — and a variable cannot stand there: this spike is generic over types, not over type constructors. A [$t] inside the arguments is ordinary. *) | Ast.Tapp (_, args) -> List.iter ty args | Ast.Tfn (ps, r) -> List.iter ty ps; ty r in List.iter (fun (p : Ast.field) -> ty p.Ast.fty) fn.Ast.params; (match fn.Ast.ret with Some r -> ty r | None -> ()); List.rev !acc (* Bind the variables in a parameter's written type from the type an argument turned out to have. Odin's [is_polymorphic_type_assignable], structurally and with the same rule: a variable already bound must match what it is bound to, so [(pair 1 2.0)] over [a $t b $t] is a refusal and not a second instantiation. *) let rec bind_ty subst (pat : Types.t) (arg : Types.t) = match pat, arg with | Types.Var v, a -> (match List.assoc_opt v !subst with | None -> subst := (v, a) :: !subst; true | Some b -> Types.equal a b) | Types.Slice p, Types.Slice a | Types.Ptr p, Types.Ptr a | Types.Vec p, Types.Vec a | Types.Pool p, Types.Pool a | Types.Handle p, Types.Handle a | Types.Option p, Types.Option a -> bind_ty subst p a | Types.Array (n, p), Types.Array (m, a) -> Int64.equal n m && bind_ty subst p a | Types.Map (k, v), Types.Map (k', v') -> bind_ty subst k k' && bind_ty subst v v' | Types.Fn (ps, r), Types.Fn (ps', r') -> List.length ps = List.length ps' && List.for_all2 (bind_ty subst) ps ps' && bind_ty subst r r' (* Nothing generic left on the pattern side: this is ordinary type equality, and [Never] fits anywhere exactly as it does elsewhere. *) | p, a -> Types.fits ~expected:p ~actual:a let rec subst_ty subst (t : Types.t) = match t with | Types.Var v -> (match List.assoc_opt v subst with Some c -> c | None -> t) | Types.Slice e -> Types.Slice (subst_ty subst e) | Types.Array (n, e) -> Types.Array (n, subst_ty subst e) | Types.Map (k, v) -> Types.Map (subst_ty subst k, subst_ty subst v) | Types.Ptr e -> Types.Ptr (subst_ty subst e) | Types.Vec e -> Types.Vec (subst_ty subst e) | Types.Pool e -> Types.Pool (subst_ty subst e) | Types.Handle e -> Types.Handle (subst_ty subst e) | Types.Option e -> Types.Option (subst_ty subst e) | Types.Fn (ps, r) -> Types.Fn (List.map (subst_ty subst) ps, subst_ty subst r) | t -> t (* Does this resolved type still mention a variable? *) let rec generic_ty (t : Types.t) = match t with | Types.Var _ -> true | Types.Slice e | Types.Array (_, e) | Types.Ptr e | Types.Vec e | Types.Pool e | Types.Handle e | Types.Option e -> generic_ty e | Types.Map (k, v) -> generic_ty k || generic_ty v | Types.Fn (ps, r) -> List.exists generic_ty ps || generic_ty r | _ -> false (* The refusal plan.org's Types section asks for, in one place so that every operator says the same thing: with no constraints a type variable supports only what *every* type supports, so [=], [<], [+] and [hash] over one are rejected rather than silently instantiated at whatever type the first call site happened to use. With [where] there are now two ways out and the message names both: declare the predicate, or take the operation as a function value the way [sort-by!] does. Declaring it is the one that keeps the call site short, which is the whole reason predicates exist — under the no-constraint rule [(sort! xs)] had to become [(sort-by! xs (fn [a b] (< a b)))] at every call site in the corpus. *) let unconstrained env loc op ~needs (t : Types.t) = if generic_ty t then match tyvar_of t with | Some v when declares env.tvpreds v needs -> () | _ -> Loc.failk "check/unconstrained-type-variable" loc "%s over the type variable %s is refused: a type variable supports \ only what it is declared to support, and nothing here says %s is \ %s. Write {:where (%s $%s)} at the head of the body, or take the \ operation as a parameter — a (Fn [%s %s] ...) — and call it here" op (Types.to_string t) (Types.to_string t) needs needs (Types.to_string t) (Types.to_string t) (Types.to_string t) (* How a concrete type is spelled inside an instantiation's name. The prelude already writes this by hand — [filter-i32], [sum-f32], [append-i64] — so a generated name reads like the handwritten one it replaces, which is what a backtrace, a [Reach] edge and a dev-build cell all end up showing. [Types.to_string] cannot serve: [[i32]] and [(Vec i32)] are not symbols. *) let rec mangle_ty (t : Types.t) = match t with | Types.Unit -> "unit" | Types.Slice e -> "slice-" ^ mangle_ty e | Types.Array (n, e) -> Printf.sprintf "arr%Ld-%s" n (mangle_ty e) | Types.Map (k, v) -> Printf.sprintf "map-%s-%s" (mangle_ty k) (mangle_ty v) | Types.Ptr e -> "ptr-" ^ mangle_ty e | Types.Vec e -> "vec-" ^ mangle_ty e | Types.Pool e -> "pool-" ^ mangle_ty e | Types.Handle e -> "handle-" ^ mangle_ty e | Types.Option e -> "opt-" ^ mangle_ty e | Types.Fn (ps, r) -> Printf.sprintf "fn-%s-to-%s" (String.concat "-" (List.map mangle_ty ps)) (mangle_ty r) | t -> Types.to_string t (* ── The runaway instantiation, refused by name rather than by depth ──── [(defn grow [x $t] () (grow [x x]))] asks for a copy at [[t]], which asks for one at [[[t]]], forever. Before this the checker did not fail, it *hung*, and [Session.eval] runs the same code — so what hung was [C-c C-c], with the dev daemon wedged behind it and nothing to show the editor. That is the project's stated priority stopped by three lines of ordinary-looking Flan, which is why this is a refusal and not a cap. The spike stopped it with a depth counter refusing past 32. A number is the wrong thing to say: 32 is not in the program, the programmer cannot act on it, and a legitimate deep instantiation and a runaway one look identical in the message. **The structural test is exact.** A generic that is already on the chain and is being asked for again at a type that *contains* the type it was asked for before is growing, and growing without a smaller case is not going to stop. A generic that recurses at the *same* types never reaches here — the cache entry goes in before the body is checked — and one that recurses at a *smaller* or unrelated type is fine and stays fine. The message prints the chain, which is what the programmer can act on: each link is a call site and a type, and the place the type started growing is visible in the list. Odin has no cap of its own to copy, so there was nothing to borrow and this is the whole design. The depth backstop below stays as a backstop only: it catches a growth this test does not recognise, and it is never the thing the message is about. *) let rec occurs_in ~needle (t : Types.t) = Types.equal needle t || match t with | Types.Slice e | Types.Array (_, e) | Types.Ptr e | Types.Vec e | Types.Pool e | Types.Handle e | Types.Option e -> occurs_in ~needle e | Types.Map (k, v) -> occurs_in ~needle k || occurs_in ~needle v | Types.Fn (ps, r) -> List.exists (occurs_in ~needle) ps || occurs_in ~needle r | _ -> false (* [b] is [a] with something built around it: same shape, strictly bigger. *) let grows ~from_:a ~to_:b = List.length a = List.length b && List.for_all2 (fun x y -> occurs_in ~needle:x y) a b && not (List.for_all2 Types.equal a b) let runaway env loc gname cparams = let chain_text () = String.concat "\n " (List.map (fun (g, ps, l) -> Printf.sprintf "%s at (%s), asked for at %s" g (String.concat " " (List.map Types.to_string ps)) (Loc.to_string l)) (env.chain @ [ (gname, cparams, loc) ])) in let earlier = List.find_opt (fun (g, ps, _) -> String.equal g gname && grows ~from_:ps ~to_:cparams) env.chain in (match earlier with | Some _ -> Loc.failk "check/runaway-instantiation" loc "%s instantiates itself without end. Each copy asks for another at a \ type built around the one before, so there is no last copy to \ generate:\n %s\nA generic function may call itself, but not at a \ type built out of its own type variable — the argument has to get \ smaller, or stay the same" gname (chain_text ()) | None -> ()); (* The backstop. Nothing known reaches it; it exists so that a growth the test above does not recognise is still a refusal with the chain in it rather than a hang. *) if List.length env.chain >= 64 then Loc.failk "check/runaway-instantiation" loc "%s has been instantiated 64 deep and is still going:\n %s" gname (chain_text ()) (* [check_fn] is defined after the expression checker and an instantiation is made from inside it, so the knot is tied here and closed at the bottom of the file. One forward reference rather than moving a 90-line function. *) let check_fn_ref : (env -> Ast.fn -> Tast.fn) ref = ref (fun _ _ -> assert false) (* ── Small helpers over the AST ────────────────────────────────────── *) (* Untyped literals: their machine type comes from context, so when one is an operand of a binary operator we look at the *other* operand first. *) let is_literal (e : Ast.expr) = match e.Ast.e with Ast.Int _ | Ast.Float _ | Ast.Byte _ -> true | _ -> false (* [addr] takes the address of a place, but the parser only builds places for [set]. Recover one from the expression it parsed instead. *) let place_of_expr (e : Ast.expr) : Ast.place option = match e.Ast.e with | Ast.Var s -> Some (Ast.Pvar s) | Ast.Field (t, f) -> Some (Ast.Pfield (t, f)) | Ast.Call ({ Ast.e = Ast.Var "at"; _ }, t :: idx) when idx <> [] -> Some (Ast.Pindex (t, idx)) | Ast.Call ({ Ast.e = Ast.Var "deref"; _ }, [ p ]) -> Some (Ast.Pderef p) | _ -> None let mk loc ty e : Tast.expr = { Tast.e; ty; loc } let unit_at loc = mk loc Types.Unit Tast.Unit (* A source location as a value, for a runtime trap that has to name the site rather than the runtime. The bounds and slice traps get theirs from [Emit], which renders the [Loc.t] it is already carrying; a trap reached through a plain runtime call has no such carrier, so the string is built here and crosses as ptr+len like any other. *) let here loc = mk loc Types.String (Tast.Str (Loc.to_string loc)) (* A runtime call, with the result type spelled at the site. *) let rt loc ty sym args = mk loc ty (Tast.Prim (Tast.Rt sym, args)) (* ── The allocation registry's note, NEXT.md ─────────────────────────── One after every operation that may have allocated — which is *here*, and nowhere else, because here is the only place the concrete type is known. A Flan struct is exactly its C layout with no header and no tag word, so nothing at run time can say what is at an address; the allocator's caller knew, and this is the caller writing it down. The type is spelled with [Types.to_string], the same spelling a slot fingerprint and a DWARF node already key on, so a name that appears in a registry answer is a name the programmer wrote. It is built unconditionally and dropped by the backend in a release build (see [Emit]'s [Rt] arm). The checker does not know which kind of build this is and must not learn: a note that existed only in a dev build would make the two builds different *trees*, and every pass between here and the backend would have to agree about which one it was looking at. [target] is the container, passed by address like every other container operation; the extent comes off its header in the runtime, because the header is the only thing that knows where the storage landed. *) let reg_note loc sym (target : Tast.expr) sizes ty = rt loc Types.Unit sym ((target :: sizes) @ [ mk loc Types.String (Tast.Str (Types.to_string ty)) ]) (* [(do attempt note)] — the note runs only once the guard's retry loop has stopped, so it describes the storage the program ended up with rather than one of the attempts that failed. *) let with_note loc (guarded : Tast.expr) (note : Tast.expr) = mk loc Types.Unit (Tast.Do [ guarded; note ]) (* ── Reading a file at compile time, decision 1 ──────────────────────── The path is a *literal*, because the bytes have to be in hand before any value exists — this is Odin's rule too (check_load_directive rejects anything that is not Addressing_Constant) and it is what makes the result cost nothing at run time. It resolves relative to the directory of the file the form is written in, which is again Odin's rule (dir_from_path of the call's file). Relative to the compiler's working directory would make a package's assets depend on where flan was invoked from, which is the thing that cannot be right. An absolute path is taken as written. *) let embed_path loc (p : Ast.expr) = match p.Ast.e with | Ast.Str "" -> Loc.fail p.Ast.loc "an embedded path cannot be empty" | Ast.Str s when Filename.is_relative s -> let base = Filename.dirname loc.Loc.file in if String.equal base "" then s else Filename.concat base s | Ast.Str s -> s | _ -> Loc.fail p.Ast.loc "an embedded path must be a literal string — the bytes are read at \ compile time, so there is nothing here to compute it from" (* The whole read is guarded, not only the open. On Linux [open_in_bin] on a *directory* succeeds and [in_channel_length] answers a number; the read is where EISDIR arrives. Guarding only the open therefore turned (embed "dir") — someone who meant embed-dir — into an uncaught OCaml exception out of the checker, which is the one way a user can make the compiler crash rather than refuse. *) let read_embed_file path loc = match let ch = open_in_bin path in Fun.protect ~finally:(fun () -> close_in_noerr ch) (fun () -> really_input_string ch (in_channel_length ch)) with | s -> s | exception Sys_error msg -> if Sys.file_exists path && (try Sys.is_directory path with Sys_error _ -> false) then Loc.fail loc "cannot embed %s: it is a directory — (embed-dir \"...\") embeds one \ of those, as a [n EmbedFile]" path else Loc.fail loc "cannot embed %s: %s" path msg | exception End_of_file -> Loc.fail loc "cannot embed %s: it changed size while being read" path (* Non-recursive, files only, sorted by name — the three things Odin's #load_directory settles, and the sort is the one that matters most here: readdir order is filesystem-dependent, so an unsorted embed would make the emitted .ll differ between two builds of identical sources. *) let read_embed_dir path loc = let names = match Sys.readdir path with | exception Sys_error msg -> Loc.fail loc "cannot embed %s: %s" path msg | a -> Array.to_list a in (* [Sys.is_directory] *raises* on a path that does not resolve, so the existence test has to come first: a dangling symlink in an embedded directory would otherwise crash the compiler before it was ever asked about. Non-recursive and files only, which is Odin's rule too. *) let files = List.filter (fun n -> let full = Filename.concat path n in Sys.file_exists full && not (try Sys.is_directory full with Sys_error _ -> true)) names in List.map (fun n -> (n, read_embed_file (Filename.concat path n) loc)) (List.sort String.compare files) let i64_at loc n = mk loc (Types.Int Types.I64) (Tast.Int (n, Types.I64)) (* spec-memory.md, "Alignment": the number is produced where the concrete element type is known, which without generics is simply the call site. *) let size_of loc t = mk loc (Types.Int Types.I64) (Tast.Prim (Tast.SizeOf t, [])) let align_of loc t = mk loc (Types.Int Types.I64) (Tast.Prim (Tast.AlignOf t, [])) (* The address of an expression, place or not: the type-erased runtime takes the element [push] copies by pointer. *) let addr_of loc (e : Tast.expr) = mk loc (Types.Ptr e.Tast.ty) (Tast.Prim (Tast.AddrOf, [ e ])) (* ── The region requirement, emitted ─────────────────────────────────── spec-memory.md's arena rule, and the whole of what replaced the three refusals a container of owning elements used to meet at its *type*. The question those refusals asked was about teardown: the type-erased runtime copies and releases slots bytewise, so a [free] would release the slots and leave everything inside them stranded. A region never releases a slot — [free-all] takes the whole thing, inner blocks included, because they came out of the same region — so the premise does not hold there and the refusal was over-broad. What could not move with it is *where* the question is asked. [can-free] is a capability on an allocator value, read at run time, and [with-allocator] rebinds a dynamic variable, so the tier a [(vec-new)] will meet is not a property of the place its type is written. The compile-time half is therefore only the decision to ask — [region_only], a property of the element type and settled here — and the run-time half is the answer. One branch per container and never per element, which spec-memory.md fixes and which is a performance decision before it is a safety one: the alternative is a walk at release, and a walk at release is the registry of destructors the frame tier's reset exists to not have. Emitted at every site that can *allocate* for such a container, not only at its construction, and the extra sites are not belt and braces. ZII means a container can exist without ever passing through [vec-new]: a data type case's field left out of a literal, a [(defvar xs (Vec Value))] a global starts as. Those are zeroed, they have no allocator at all, and the first [push] is what adopts the context — so a guard only at the construction would have a hole exactly the width of ZII. The *container* is what is asked in both places, and at a construction that means the guard runs immediately after the init rather than before it. The allocator is right there as an argument of the site, but naming it twice in the emitted tree is not free: it is an arbitrary expression, and [(vec-new Value (arena-new 4096))] would build two arenas and guard the one it threw away. The container has recorded it by the time the init returns, so asking the container asks that one expression exactly once. It is still the point of construction and still before anything is put in; what a trap there costs is the empty block just taken, on a process that is about to die. At a growth the guard runs first, because there the container already exists and the allocation is what has to be stopped. A zeroed one answers from the context it is about to adopt, which is not a guess — [flan_vec_adopt] is the code that will take it, on this same call. *) let region_sym (t : Types.t) = match t with | Types.Vec _ -> "flan_vec_region_only" | Types.Map _ -> "flan_map_region_only" | Types.Pool _ -> "flan_pool_region_only" | _ -> assert false let region_check env loc (target : Tast.expr) (after : Tast.expr) = if not (region_only env target.Tast.ty) then after else mk loc after.Tast.ty (Tast.Do [ rt loc Types.Unit (region_sym target.Tast.ty) [ target; here loc ]; after ]) (* Every integer index into an array or slice is i32 at milestone 2. *) let index_ty = Types.Int Types.I32 (* A condition's type at run time is a number, and it has to be the *same* number in a module compiled later against a program already running. So it is a hash of the name and not an index into anything: an index would shift the moment a struct were added, and every handler pushed by the old code would then match the wrong type. FNV-1a over the name, 32 bits. *) let type_id name = let h = ref 0x811c9dc5 in String.iter (fun c -> h := (!h lxor Char.code c) land 0xffffffff; h := (!h * 0x01000193) land 0xffffffff) name; !h (* How a restart's parameter list is spelled, and with it what the two ends of an [invoke-restart] compare — spec-conditions.md §3's run-time check. A restart is found by name on a dynamic stack, so neither end can see the other and nothing static can be checked: what is compared at run time is this string's hash, alongside the count, and the string itself is carried so that a mismatch can say what was wanted and what was given. Comparing a 32-bit hash means two different parameter lists could in principle collide. The count is checked separately, which rules out every practical case (a collision would have to be between two lists of the same length), and the types are parenthesised so that [(Option i32)] cannot read as two parameters. *) let restart_sig tys = "(" ^ String.concat " " (List.map Types.to_string tys) ^ ")" let expect loc ~want (got : Tast.expr) = match want with | None -> got | Some w -> if Types.fits ~expected:w ~actual:got.Tast.ty then got else fail loc "expected %s, found %s" (Types.to_string w) (Types.to_string got.Tast.ty) (* Something a [break] may not jump out of, named so the refusal can say which. See [lentry]: it is a barrier and not a blanket refusal, so a loop written wholly inside one keeps its own perfectly good local break. Outside the recursive group below because its callers hand it bodies of two shapes — one expression and a list of them — and inside it would be monomorphic. *) let barrier ctx what f = let loops = ctx.loops in ctx.loops <- Lbarrier what :: loops; let r = f () in ctx.loops <- loops; r (* ── Expressions ───────────────────────────────────────────────────── *) (* ── (Map K V): the key's hash and equality pair ──────────────────────── spec-memory.md restricts the first implementation to built-in structural key types — integers, enums, strings, fixed arrays, and value structs composed recursively from those — and makes equality and hashing for them compiler-provided structural operations rather than type classes. So there is no dispatch to design: every key type resolves, here, to a pair of symbols, and the pair is passed to the type-erased runtime the way Odin hangs its two contextless procs off a Map_Info. Most key types need no emitted function at all. A key whose equality is bytewise and whose bytes are all present is served by one runtime pair over (pointer, size), which is what [bytewise_key] identifies. Two kinds are not: - a [string] is ptr+len and its bytes are elsewhere, so two equal strings at different addresses must still hash the same; - a struct may have padding, whose bytes are indeterminate, so two structs that are equal field by field can differ bytewise — and it may hold a string, which brings the first problem inside it. A struct therefore gets a pair emitted for it, walking its fields, and that is the only case that does. *) let rec bytewise_key = function | Types.Int _ | Types.Enum _ | Types.Bool -> true | Types.Array (_, t) -> bytewise_key t | _ -> false let hash_ty = Types.Int Types.U64 (* A context for a function the checker is about to invent. Nothing is reachable from it: no outer scope, no defers, and [defer_ok] false, because none of these is a body anyone wrote. *) let invented_ctx env ret = { env; ret; slots = 0; slot_tys = []; slot_names = []; scope = []; defers = []; outer = []; outer_what = None; in_frames = None; loops = []; tail = false; in_defer = false; defer_ok = false; defer_block = "a nested form"; dead = []; borrow = false; owner = "" } (* The address of field [i] of the struct the pointer in slot [p] points at. *) let field_addr_of loc sty fty p i = let target = mk loc sty (Tast.Deref (mk loc (Types.Ptr sty) (Tast.Local p))) in mk loc (Types.Ptr fty) (Tast.Addr (Tast.Pfield (target, i))) (* The pointer form is what a Map_Info holds; the direct form is what an emitted hasher calls. See flan_rt.c on why they are two symbols. *) let direct = function | "flan_hash_flat" -> "flan_key_hash_flat" | "flan_eq_flat" -> "flan_key_eq_flat" | "flan_hash_str" -> "flan_key_hash_str" | "flan_eq_str" -> "flan_key_eq_str" | s -> s (* The pair for [k]: (hash, equality), each a symbol to be taken the address of. Emits a function for a struct key the first time it sees one, and finds it in [env.lifted] every time after — the name is derived from the type, so two maps with the same key type share one pair. *) let rec key_pair env loc (k : Types.t) : Tast.fnref * Tast.fnref = match k with (* A hash and an equality for a type variable would have to be *chosen*, and nothing here can choose: the pair is emitted as concrete symbols and the concrete type does not exist until the instantiation. Refused rather than assumed — falling through to [bytewise_key] would hash whatever bytes the variable turned out to have, which is the wrong answer for a [string] and for any struct with padding. **This arm is a backstop and nothing normal reaches it.** Two things get there first. Inside an instantiation [env.subst] has already made [k] concrete, so there is no variable left. Outside one — in the abstract pass over a generic body — the map operations are *deferred* ([deferred_key] below): a key that is a variable declared [hashable?] never asks for a pair here, and a variable that is not declared it never gets as far as a [(Map $t V)] to operate on, because [map_type] refuses the type where it is written. What is left for this arm is a key that is a variable by some route neither of those covers, and the honest answer to that is still a refusal rather than a guessed pair. *) | Types.Var v -> Loc.failk "check/generic-map-key" loc "a map keyed by the type variable %s has no hash and no equality here: \ both are emitted as concrete symbols chosen from the concrete key \ type, and there is none until this generic is instantiated. The map \ operations are deferred to the instantiation when {:where (hashable? \ $%s)} is declared — declare it, or write the operation in a function \ over the concrete key type and call that" v v | Types.String -> Tast.Rtfn "flan_hash_str", Tast.Rtfn "flan_eq_str" | t when bytewise_key t -> Tast.Rtfn "flan_hash_flat", Tast.Rtfn "flan_eq_flat" | Types.Named n when Hashtbl.mem env.structs n -> struct_key_pair env loc n (* A data type key would have to hash the tag and then only the bytes the case in hand actually uses — the rest of the payload is indeterminate, exactly as a struct's padding is, so hashing the blob would make two equal values hash differently. That is a per-case walk driven by a switch, which is a different shape from the field list [struct_key_pair] emits and which nothing has yet wanted. Refused by name rather than written untested. *) | Types.Named n when Hashtbl.mem env.datas n -> fail loc "%s is a data type, and a data type is not a map key: the payload past \ the case in hand is indeterminate, so hashing the bytes would make two equal \ values hash differently. Hashing one needs a per-case walk, which is \ not written — key on the tag, or on a struct holding what you meant" n (* And an untagged union is refused for the half of that reason which has nothing to do with a tag: a member smaller than the union leaves the rest of the storage indeterminate, so two values that agree about every byte anybody wrote hash differently. There is no per-member walk to write here either — nothing records which member was written, which is the type. *) | Types.Named n when Hashtbl.mem env.unions n -> fail loc "%s is a union, and a union is not a map key: a member narrower than \ the union leaves the rest of the bytes indeterminate, so two values \ that agree about everything written would still hash differently. Key \ on the member you meant" n | Types.Array (_, e) -> (* A fixed array of a struct or of strings would need the same per-element walk a struct key gets, driven by a loop rather than by a field list. Nothing has wanted one, so it is refused by name rather than written untested — and refused with the shape that does work named beside it. *) fail loc "a fixed array is a map key only when its elements are compared \ bytewise, and %s is not — a struct or a string element needs a \ per-element walk that is not written. A struct key holding the array \ works, because a struct key is walked field by field" (Types.to_string e) | Types.Float _ -> (* Not a milestone question, which is why it is said separately: NaN is not equal to itself, and 0.0 and -0.0 are equal while differing bytewise. A float key therefore has no equality for a hash map to use, whatever the implementation does. *) fail loc "a float is not a map key: NaN is not equal to itself, and 0.0 and -0.0 \ are equal but differ bytewise, so there is no equality here for a map \ to hash. Key on an integer, or on a quantised integer of your choosing" | other -> fail loc "%s is not a map key. The first implementation takes integers, enums, \ bools, strings, fixed arrays of those, and value structs composed of \ those (spec-memory.md, \"Maps — first implementation\"). A Ptr, a \ slice, a Vec or a Map would hash an address rather than what it points \ at, which is a different operation" (Types.to_string other) and struct_key_pair env loc n = let hname = "map/hash/" ^ n and ename = "map/eq/" ^ n in let known name = List.exists (fun (f : Tast.fn) -> f.Tast.name = name) env.lifted in if known hname then Tast.Flanfn hname, Tast.Flanfn ename else begin let sty = Types.Named n in let fields = (Hashtbl.find env.structs n).Tast.fields in if fields = [] then fail loc "%s has no fields, so every value of it is equal to every other — a \ map keyed on it holds at most one entry, which is not a map" n; let hparams = [ Types.Ptr sty; hash_ty; Types.Int Types.I64 ] in let eparams = [ Types.Ptr sty; Types.Ptr sty; Types.Int Types.I64 ] in (* Registered before the fields are walked, so a struct reached twice through two different fields emits one pair and not two. A struct cannot contain itself by value, so there is no cycle to break — only sharing. The body is filled in below; nothing can call these in between. *) let placeholder name ret params = { Tast.name; params; slots = Array.of_list params; snames = Array.make (List.length params) None; ret; body = []; fdefers = []; fparent = None; floc = loc } in env.lifted <- placeholder hname hash_ty hparams :: placeholder ename (Types.Int Types.I8) eparams :: env.lifted; (* The hash: seed, then one combine per field, in declaration order. Each field is hashed by its own pair — the same recursion, so a string field hashes its bytes and a nested struct hashes field by field. Padding is never reached, because nothing here addresses anything but a field. *) let hctx = invented_ctx env hash_ty in let kp = fresh_slot ~name:"key" hctx (Types.Ptr sty) in let seed = fresh_slot ~name:"seed" hctx hash_ty in ignore (fresh_slot ~name:"size" hctx (Types.Int Types.I64)); let acc = fresh_slot ~name:"h" hctx hash_ty in let steps = List.mapi (fun i (fl : Tast.field) -> let fty = fl.Tast.fty in let h, _ = key_pair env loc fty in let args = [ field_addr_of loc sty fty kp i; mk loc hash_ty (Tast.Local seed); size_of loc fty ] in let one = match h with | Tast.Rtfn s -> rt loc hash_ty (direct s) args | Tast.Flanfn s | Tast.Fnval s -> mk loc hash_ty (Tast.Call (s, args)) in mk loc Types.Unit (Tast.Set (Tast.Plocal acc, rt loc hash_ty "flan_hash_combine" [ mk loc hash_ty (Tast.Local acc); one ]))) fields in let hbody = (mk loc Types.Unit (Tast.Set (Tast.Plocal acc, mk loc hash_ty (Tast.Local seed)))) :: steps @ [ mk loc hash_ty (Tast.Local acc) ] in (* The equality: one early return per field, then true. Written as returns rather than as a conjunction so that the comparison stops at the first field that differs, which for a struct with a string field is the difference between one memcmp and two. *) let ectx = invented_ctx env (Types.Int Types.I8) in let ap = fresh_slot ~name:"a" ectx (Types.Ptr sty) in let bp = fresh_slot ~name:"b" ectx (Types.Ptr sty) in ignore (fresh_slot ~name:"size" ectx (Types.Int Types.I64)); let i8 v = mk loc (Types.Int Types.I8) (Tast.Int (v, Types.I8)) in let checks = List.mapi (fun i (fl : Tast.field) -> let fty = fl.Tast.fty in let _, eq = key_pair env loc fty in let args = [ field_addr_of loc sty fty ap i; field_addr_of loc sty fty bp i; size_of loc fty ] in let call = match eq with | Tast.Rtfn s -> rt loc (Types.Int Types.I8) (direct s) args | Tast.Flanfn s | Tast.Fnval s -> mk loc (Types.Int Types.I8) (Tast.Call (s, args)) in let differs = mk loc Types.Bool (Tast.Prim (Tast.Eq, [ call; i8 0L ])) in mk loc Types.Unit (Tast.If (differs, mk loc Types.Never (Tast.Return (Some (i8 0L))), unit_at loc))) fields in let ebody = checks @ [ i8 1L ] in let finish name ret params ctx body = { Tast.name; params; slots = Array.of_list (List.rev ctx.slot_tys); snames = Array.of_list (List.rev ctx.slot_names); ret; body; fdefers = []; fparent = None; floc = loc } in env.lifted <- finish hname hash_ty hparams hctx hbody :: finish ename (Types.Int Types.I8) eparams ectx ebody :: List.filter (fun (f : Tast.fn) -> f.Tast.name <> hname && f.Tast.name <> ename) env.lifted; Tast.Flanfn hname, Tast.Flanfn ename end (* The pair as two expressions, ready to be passed. Their Flan type is [Alloc]: an opaque pointer-width value with no user-writable constructor, which is all the backend needs and all any Flan type ever says about it. *) let key_fns env loc k = let h, e = key_pair env loc k in mk loc Types.Alloc (Tast.FnAddr h), mk loc Types.Alloc (Tast.FnAddr e) (* ── The map operations, deferred to the instantiation ───────────────── True when the key is a type variable, which means the operation cannot be built here and must be answered by the copy: [key_fns] emits concrete symbols and there is no concrete key type yet. The caller checks its arguments first and then returns a placeholder of the operation's own type, exactly as [print] does — see the allow-list comment at the [print] arm for what being on that list costs and why these are on it. The predicate is *required* before deferring, and that is the whole safety argument: with {:where (hashable? $t)} in the signature, the instantiation refuses at the call site against a requirement the author wrote down. A variable with no such clause is refused here and now, at the definition, which is where the abstract pass wants every refusal that has nothing to point at. In practice [map_type] has already refused such a signature where the type was written; this repeats it rather than relying on that, the same way [key_pair] repeats [map_type]'s key check. *) let deferred_key env loc what (k : Types.t) = match k with | Types.Var v -> if not (declares env.tvpreds v "hashable?") then Loc.failk "check/generic-map-key" loc "%s over a map keyed by the type variable %s is refused: the hash and \ the equality are emitted as concrete symbols chosen from the \ concrete key type, and nothing here declares %s hashable. Write \ {:where (hashable? $%s)} at the head of the body — then the \ operation is deferred to each instantiation, and a call site that \ asks for a key type that cannot be hashed is refused there, against \ the clause" what (Types.to_string k) (Types.to_string k) v; true | _ -> false let rec check ctx ?want (e : Ast.expr) : Tast.expr = let loc = e.Ast.loc in (* Read the permission this form was given and withdraw it in the same breath, so that nothing reached from here inherits it. The two callers that may grant it — [check_fn]'s body walk and [check_let]'s, below — grant it again before the *next* form rather than once around the body. *) let defer_ok = ctx.defer_ok in ctx.defer_ok <- false; (* The same read-and-withdraw, for the same reason: a [recur] is in tail position only if *this* form was, and nothing reached from here inherits it unless the arm below hands it on deliberately. *) let tail = ctx.tail in ctx.tail <- false; match e.Ast.e with | Ast.Int n -> int_literal loc ~want n | Ast.Byte b -> int_literal loc ~want ~default:Types.U8 (Int64.of_int b) | Ast.Float x -> let k = match want with | Some (Types.Float k) -> k | Some other when other <> Types.Never -> fail loc "expected %s, found the float literal %g" (Types.to_string other) x | _ -> Types.F64 in mk loc (Types.Float k) (Tast.Float (x, k)) | Ast.Str s -> expect loc ~want (mk loc Types.String (Tast.Str s)) | Ast.Kw k -> (* A keyword resolves at compile time against the enum the site expects, and a typo is an error here rather than a wrong number at run time (plan.org, settled: keywords at typed call sites). It has no meaning without that expectation — there is no keyword type to fall back on. *) (match want with | Some (Types.Enum name) -> let members = Hashtbl.find ctx.env.enums name in (match List.assoc_opt k members with | Some v -> mk loc (Types.Enum name) (Tast.Int (v, Types.I32)) | None -> fail loc "%s has no member :%s — it has %s" name k (String.concat " " (List.map (fun (m, _) -> ":" ^ m) members))) | Some other -> fail loc ":%s is an enum member, but %s is expected here" k (Types.to_string other) | None -> fail loc ":%s only means something where an enum type is expected — there is \ no keyword type" k) | Ast.Quote _ -> unimplemented loc "a quoted symbol (restart names)" 6 | Ast.Var name -> var ctx loc ~want name | Ast.Do body -> ctx.tail <- tail; block ctx ?want loc body (* [defer_ok] rides through: a [let] at the top level of a function body has exactly the function's extent, and so does a [let] nested inside one. [tail] rides through for the same shape of reason: a [recur] written as the last form of a [let] inside a loop body is in the loop's tail. *) | Ast.Let (bs, body) -> check_let ctx ~tail ?want ~defer_ok loc bs body | Ast.If (c, t, e') -> check_if ctx ~tail ?want loc c t e' | Ast.While (label, c, body) -> let c = check ctx ~want:Types.Bool c in let body = in_loop ctx ?label (fun () -> scoped ctx (fun () -> map_lr (fun b -> check ctx b) body)) in (* No latch: a [while] has nothing to run between the body and the test, so a [continue] can branch straight at the condition. *) expect loc ~want (mk loc Types.Unit (Tast.While (c, body, []))) (* [Never], as [exit] and [return] are: nothing after one of these runs, and an [if] arm that ends in a break does not have to agree with the other. *) (* (loop [x 0 acc 1] body ...) — a loop that answers with the value of its body, and the only place a [recur] may stand. Not an IR node: it is a [let] over the names, a [While] whose condition is [true], and a jump. See [check_loop]. *) | Ast.Loop (bs, body) -> check_loop ctx ?want loc bs body | Ast.Recur args -> check_recur ctx ~tail loc args | Ast.Break label -> mk loc Types.Never (Tast.Break (loop_target ctx loc "break" label)) | Ast.Continue label -> mk loc Types.Never (Tast.Continue (loop_target ctx loc "continue" label)) | Ast.Return v when ctx.in_frames <> None -> ignore v; (* The frames are pushed and popped around the body, so an early exit would leave them on the handler or restart stack pointing into a frame that has gone. Rejected rather than left to corrupt it, the same rule as defer inside a block. *) fail loc "return is not allowed inside %s yet — the frames it established are \ popped on the way out and an early exit would leave them on the stack" (match ctx.in_frames with Some n -> n | None -> assert false) | Ast.Return v -> let v = match v with | None -> if not (Types.equal ctx.ret Types.Unit) then fail loc "this function returns %s, so return needs a value" (Types.to_string ctx.ret); None | Some v -> Some (check ctx ~want:ctx.ret v) in (* Whatever has been deferred *so far* runs first: a defer written below this return has not executed yet and must not fire. *) let r = mk loc Types.Never (Tast.Return v) in (match ctx.defers with | [] -> r | ds -> mk loc Types.Never (Tast.Do (ds @ [ r ]))) | Ast.Set (p, v) -> let p, pty = check_place ctx loc p in let v = check ctx ~want:pty v in expect loc ~want (mk loc Types.Unit (Tast.Set (p, v))) | Ast.Field (target, name) -> let target, sname = struct_target ctx target in let s = Option.get (fields_named ctx.env sname) in (match Tast.field_index s name with | None -> Loc.failk "check/unknown-field" loc ~notes:(declared_note ctx.env sname) "%s has no field %s" sname name | Some i -> let fty = (List.nth s.Tast.fields i).Tast.fty in expect loc ~want (mk loc fty (Tast.Field (target, i)))) | Ast.Struct (name, kvs) -> check_struct ctx ~want loc name kvs | Ast.Arr items -> check_arr ctx ~want loc items (* (array 4 rl/Vector2). Parse already assembled the whole array type, so there is nothing to infer: resolve it and hand back its all-bytes-zero value, which is what a declared array with no initialiser gets. *) | Ast.ArrayOf t -> let ty = resolve ctx.env t in expect loc ~want (mk loc ty (Tast.Zero ty)) | Ast.Match (scrutinee, arms) -> check_match ctx ~tail ?want loc scrutinee arms | Ast.Call (head, args) -> check_call ctx ~want loc head args | Ast.Unwrap (Ast.Usome, v) -> (* Unwrap Some, else early-return None from the enclosing function, so the enclosing function must itself return an Option (plan.org). *) (match ctx.ret with | Types.Option _ -> let v = check ctx v in (match v.Tast.ty with | Types.Option t -> expect loc ~want (mk loc t (Tast.UnwrapSome v)) | other -> fail loc "some takes an (Option T), found %s" (Types.to_string other)) | other -> fail loc "some early-returns None, so the enclosing function must return an \ Option; this one returns %s" (Types.to_string other)) | Ast.Unwrap (Ast.Utry, _) -> unimplemented loc "try (Result)" 6 | Ast.Fn (params, body) -> check_fn ctx ~want loc params body | Ast.Dotimes (label, name, count, body) -> check_dotimes ctx ~want loc label name count body (* (signal c) : Unit, always — spec-conditions.md §1. A handler that returns normally leaves the signalling function to carry on, and with nothing matching this is a no-op, so nothing about it alters control flow. That is what makes it checkable here rather than needing the transfer machinery restart-case will want. *) | Ast.Signal (kind, c) -> let c = check ctx c in let name = match c.Tast.ty with | Types.Named n -> n | t -> fail c.Tast.loc "a condition is a struct, not %s — matching is by type and there is \ no condition hierarchy" (Types.to_string t) in (* §1 and §2. [signal] is Unit whatever it finds; [error] is Never, because the only way past it is a handler that transfers — one that returns normally has not answered it, and the program stops. *) let ty, kind = match kind with | Ast.Ssignal -> (Types.Unit, Tast.Ssignal) | Ast.Serror -> (Types.Never, Tast.Serror) in expect loc ~want (mk loc ty (Tast.Signal (kind, type_id name, c))) | Ast.HandlerBind (clauses, body) -> check_handler_bind ctx ?want loc clauses body (* spec-conditions.md §3–§6: the transfer. Neither of these is a call — one establishes frames around a body, and the other leaves the function it is written in — so both are their own nodes all the way down. *) | Ast.RestartCase (body, clauses) -> check_restart_case ctx ?want loc body clauses | Ast.InvokeRestart (name, args) -> (* Never: control resumes at the restart-case, which yields the clause's value to *its* continuation, so nothing here has a value and nothing after it runs. The lookup is at run time because restarts are dynamically scoped and named — §4 — and so, for the same reason, is the check that these arguments are the ones the clause takes (§3). *) if ctx.in_defer then fail loc "invoke-restart is not allowed inside a defer — a defer is the cleanup \ a transfer runs on its way out, so starting one there would leave \ this function's defers half run with two targets and no way to \ choose"; let args = map_lr (fun a -> check ctx a) args in List.iter (fun (a : Tast.expr) -> match a.Tast.ty with | Types.Unit | Types.Never -> fail a.Tast.loc "a restart argument must be a value, and this one is %s" (Types.to_string a.Tast.ty) | _ -> ()) args; let sg = restart_sig (List.map (fun (a : Tast.expr) -> a.Tast.ty) args) in (* Evaluated into slots first, so that an argument which transfers on its own is guarded before this form aims the channel, and so that a call written in an argument is on the ordinary walk rather than hidden inside a node that [Reach] and [Load] treat as a leaf. *) let binds = List.map (fun (a : Tast.expr) -> (fresh_slot ctx a.Tast.ty, a)) args in let locals = List.map (fun (s, (a : Tast.expr)) -> mk a.Tast.loc a.Tast.ty (Tast.Local s)) binds in let invoke = mk loc Types.Never (Tast.InvokeRestart (type_id name, name, locals, sg, type_id sg, loc)) in expect loc ~want (if binds = [] then invoke else mk loc Types.Never (Tast.Let (binds, [ invoke ]))) | Ast.Defer forms -> (* Registering is the whole of it: the forms are checked here, where they can see the scope they are written in, and the node left behind is [unit]. [check_fn] splices the registered list onto both exit paths. [defer_ok] is true for a top-level form of the body and for a form in a [let] whose extent is the body — see the field's comment. Anywhere else the cleanup would run at function exit rather than at the exit of the construct it was written in, so it is refused, and named. *) if not defer_ok then fail loc "defer is not allowed inside %s — a defer is copied into every exit \ path of the function, so it always registers and always runs at \ function exit. Write it at the top level of the function body, or in \ a let that is (a let has the function's extent, because nothing is \ released at scope exit)" ctx.defer_block; register_defer ctx loc forms and int_literal loc ~want ?(default = Types.I32) n = match want with | Some (Types.Int k) -> mk loc (Types.Int k) (Tast.Int (in_range loc k n, k)) (* An untyped integer constant is usable where a float is wanted, as in Odin. A float literal is never usable where an integer is wanted. *) | Some (Types.Float k) -> mk loc (Types.Float k) (Tast.Float (Int64.to_float n, k)) | Some other when other <> Types.Never -> fail loc "expected %s, found the integer literal %Ld" (Types.to_string other) n | _ -> mk loc (Types.Int default) (Tast.Int (in_range loc default n, default)) (* Arithmetic wraps, but a literal that does not fit its type is a typo, not a wrap — 300 is never what someone meant by a u8. *) and in_range loc k n = let bits = Types.bits k in let ok = if Types.signed k then bits = 64 || (Int64.compare n (Int64.neg (Int64.shift_left 1L (bits - 1))) >= 0 && Int64.compare n (Int64.shift_left 1L (bits - 1)) < 0) else if bits = 64 then (* A u64 literal is its 64-bit pattern, so anything at or above 2^63 arrives here as a negative [int64] and is still in range — 0xcbf29ce484222325 is a real u64 and not an error. The cost is that a negative *decimal* literal is accepted as a u64 too, because the reader records only the value and not how it was written. Narrower unsigned types keep the strict check, which is where a typo like 300 for a u8 actually shows up. *) true else Int64.compare n 0L >= 0 && Int64.compare n (Int64.shift_left 1L bits) < 0 in if ok then n else fail loc "%Ld does not fit in %s" n (Types.ikind_name k) and var ctx loc ~want name = match name with | "true" | "false" -> expect loc ~want (mk loc Types.Bool (Tast.Bool (name = "true"))) | "None" -> (match want with | Some (Types.Option t) -> mk loc (Types.Option t) Tast.None_ | Some other when other <> Types.Never -> fail loc "expected %s, found None" (Types.to_string other) | _ -> fail loc "nothing here says what None is an Option of — annotate the \ function's return type or the binding") (* spec-memory.md puts the allocator in the calling convention as [context/allocator] and [context/temp]. They read as names rather than calls because that is how the spec writes them, and they are dynamic variables at run time rather than extra parameters — see docs/BUILT.md for why the literal reading of "calling convention" is deferred. *) | "context/allocator" -> expect loc ~want (mk loc Types.Alloc (Tast.Prim (Tast.Rt "flan_context_allocator", []))) | "context/temp" -> expect loc ~want (mk loc Types.Alloc (Tast.Prim (Tast.Rt "flan_context_temp", []))) | _ -> match lookup ctx name with | Some b -> if move_only ctx.env.tvpreds b.bty then moved ~ty:b.bty ctx loc name b.slot; expect loc ~want (mk loc b.bty (Tast.Local b.slot)) | None -> match Hashtbl.find_opt ctx.env.globals name with | Some (ty, _) -> if Types.is_move_only ty then global_borrow ctx loc name ty; expect loc ~want (mk loc ty (Tast.Global name)) | None -> match Hashtbl.find_opt ctx.env.cases name with (* A case with no fields is a whole value on its own, so it is written as a name and not as a call — the same shape [None] has, and for the same reason: there is nothing to put in the braces. A case that does have fields is refused here rather than silently zeroed, because ZII on a constructor would quietly produce a value nobody wrote. *) | Some (dname, c) when String.contains name '.' -> if c.Tast.vfields <> [] then fail loc "%s has fields, so it needs them — write (%s {.%s ...})" name name (List.hd c.Tast.vfields).Tast.fname; expect loc ~want (mk loc (Types.Named dname) (Tast.MakeCase (dname, c.Tast.vname, []))) | Some (dname, c) -> fail loc "%s is a case of the data type %s, and a data type value names both — \ write %s.%s" name dname dname c.Tast.vname | None -> (* A bare function name *is* the function. This is a Lisp-1 — one top-level namespace, enforced, so a defn and a defvar cannot share a name — and that is exactly what makes (map double xs) safe to read: there is no second binding of [double] for it to have meant instead, so Common Lisp's #'double would be punctuation answering a question this language does not ask. *) (match Hashtbl.find_opt ctx.env.fns name with | Some (params, ret) -> (* A foreign function is in [fns] too, and its emitted signature is C's: no transfer channel, and an aggregate flattened by the shim. Nothing could call the resulting pointer correctly, so it is refused for what it is rather than handed out. *) if Hashtbl.mem ctx.env.externs name then fail loc "%s is a foreign function, and its address is not a Flan \ function value: a Flan function's signature ends with the \ transfer channel and a C one does not. Wrap it in a defn \ and pass that" name; expect loc ~want (mk loc (Types.Fn (params, ret)) (Tast.FnAddr (Tast.Fnval name))) | None -> captured ctx loc name; Loc.failk "check/unknown-name" loc "unknown name %s" name) (* Reading a move-only local. Every read is a move unless the site said it was a borrow, which is the conservative direction: passing one to a function, binding it, returning it and [free]ing it are all moves and all reach here, and the handful of operations that only look at a container say so. *) and moved ?ty ctx loc name slot = (match List.assoc_opt slot ctx.dead with | Some where -> fail loc "%s was moved at %s and cannot be used again — %s is move-only, so \ binding, passing or returning one transfers ownership and the source \ binding is dead afterwards (spec-memory.md). That rule is what makes a \ double free unrepresentable; (clone %s) if you wanted a second one" name (Loc.to_string where) (match ty with Some t -> Types.to_string t | None -> "a Vec") name | None -> ()); if not ctx.borrow then ctx.dead <- (slot, loc) :: ctx.dead (* Reading a move-only *global*, which is the same fork as [moved] with the other answer: a global is never moved out of, so a site that would have taken ownership is refused rather than recorded. The rule this enforces is one sentence — reading a move-only global is always a borrow. It is sound for a reason that does not generalise to locals: the lifetime question, which ownership tracking exists to answer, has a constant answer here. A global lives as long as the process, so nothing may free it and nothing needs to; there is no frame whose exit it could outlive and no second owner to disagree with. What would break the argument is exactly one thing — someone taking ownership — and that is a move, and every move reaches this function because [ctx.borrow] is false everywhere except the operations that said they only look. So the dead set is not consulted and not extended. A global cannot be dead: two functions reading the same one are both borrowing it, which is why the per-function dead set that the declaration site used to argue from was never the obstacle it looked like. It could not track a global's ownership; with this rule there is no ownership to track. Mutation is not a move and is not refused. [push], [put] and [set] all take their target through [borrowed], so a global (Vec u8) is filled and grown in place, and the aliasing that raises — a push that reallocates invalidating a slice into the same Vec — is the programmer's, exactly as it is for a local (spec-memory.md, "Borrowing", and the note on [as-slice] below). Globals get no rule locals do not have: the dev build's generation word lives on the Vec and traps on a stale slice whether the Vec is a global or not. *) and global_borrow ctx loc name (ty : Types.t) = if not ctx.borrow then (* The last clause is conditional, because [clone] stopped being offerable for one of these. A global whose elements own storage is admitted — a move-only global starts zeroed and this one is no different — but cloning it is refused, on the grounds that a bytewise copy is an alias under a name that promises independence. Offering it anyway would send a reader to a second refusal, and there is no other route to an independent copy: the region owns the graph, and [free-all] is the only thing that releases any of it. *) fail loc "%s is %s, which is move-only, and a global of one is only ever \ borrowed: its lifetime is the process's, so nothing may take ownership \ of it, and this site would. A free through the new owner would leave \ every other reader of %s pointing at released memory. Read and mutate \ it where it is — (len %s), (at %s i), (push %s x), (set (at %s i) x) \ — or take a view with (as-slice %s) or a pointer with (addr %s)%s" name (Types.to_string ty) name name name name name name name (if region_only ctx.env ty then ". There is no independent copy of this one: its elements own \ storage, so a clone would alias rather than copy and is refused" else Printf.sprintf ", or an independent copy with (clone %s), which is the one of \ these that something else may own" name) (* The target of an operation that reads a container without consuming it. Only a syntactically simple target is treated as a borrow: in [(len (f v))] the call still moves [v], and setting the flag over the whole subexpression would have hidden that. *) and borrowed ctx (a : Ast.expr) f = let simple = match a.Ast.e with | Ast.Var _ | Ast.Field _ -> true | Ast.Call ({ Ast.e = Ast.Var "at"; _ }, _) -> true | _ -> false in if not simple then f () else begin let saved = ctx.borrow in ctx.borrow <- true; let r = f () in ctx.borrow <- saved; r end (* [defer_ok] is granted again before *every* form, not once before the block: [check] withdraws it as it starts, so granting it once would let the first form carry a defer and refuse the second — and two resources acquired in one [let] is the case the relaxation exists for. *) and block ctx ?want ?(defer_ok = false) loc body = match body with (* Withdrawn here too. An empty body has no last form to be the tail, so leaving the permission set would hand it to whatever is checked next. *) | [] -> ctx.tail <- false; expect loc ~want (unit_at loc) | _ -> (* A block's tail is its last form and nothing else. Callers that must not pass one on need do nothing: [check] withdrew it before they were reached, so [tail] is already false here for all of them. *) let tail = ctx.tail in let rec go = function | [ last ] -> ctx.defer_ok <- defer_ok; ctx.tail <- tail; let l = check ctx ?want last in [ l ], l.Tast.ty | x :: rest -> ctx.defer_ok <- defer_ok; ctx.tail <- false; let x = check ctx x in let rest, ty = go rest in x :: rest, ty | [] -> assert false in let body, ty = go body in mk loc ty (Tast.Do body) (* (fn [x y] BODY...) — a function value, lifted into a function of its own. The same arrangement a handler clause already uses, and deliberately so: this compiler has built and called function values internally since the Map landed, and the surface feature is that machinery given a name rather than a second one invented beside it. **No capture, and that is the scope of this milestone.** The body sees its parameters and the program's globals and nothing else; a reference to a local of the enclosing function is refused by name (see [captured]) rather than resolved to something it did not mean. That is what makes the value a bare code address with no environment behind it, which in turn is what makes it safe to pass down, return, and store: there is nothing that can outlive anything. spec-memory.md's capture cases, and escaping closures with them, stay deferred. **The parameter types come from the position.** [Ast.Fn] carries names and no types — that is the surface syntax, not an omission here — so an fn is checkable exactly where something says what is wanted. An argument position does, because [named_call] threads the callee's parameter type into each argument; a bare [(let [f (fn [x] x)])] does not, and is refused saying so. *) and check_fn ctx ~want loc (params : string list) body = let pts, ret = match want with | Some (Types.Fn (ps, r)) when List.length ps = List.length params -> ps, r | Some (Types.Fn (ps, r)) -> fail loc "this fn has %d parameter%s and %s was wanted here" (List.length params) (if List.length params = 1 then "" else "s") (Types.to_string (Types.Fn (ps, r))) | Some other when other <> Types.Never -> fail loc "expected %s, found an fn" (Types.to_string other) | _ -> fail loc "nothing here says what this fn's parameters are — an fn takes its \ types from the position it is written in, so it goes in an argument \ whose parameter is a (Fn [T ...] R), and a name already written as a \ defn goes anywhere" in (* Its own frame and its own empty scope, with [outer] kept only so that a reference to the enclosing function's locals is refused for the reason it is really refused for. *) let fctx = { env = ctx.env; ret; slots = 0; slot_tys = []; slot_names = []; scope = []; defers = []; outer = ctx.scope; outer_what = Some "an fn"; in_frames = None; loops = []; tail = false; in_defer = false; defer_ok = false; defer_block = "a nested form"; dead = []; borrow = false; owner = ctx.owner } in List.iter2 (fun n t -> ignore (bind fctx n t ~assignable:false)) params pts; let fbody = map_lr (fun e -> check fctx e) body in (* The same rule an ordinary defn's body follows: the last form is the answer, and it has to be the declared return type. *) let fbody = match List.rev fbody with | [] -> fbody | last :: rest -> List.rev (expect last.Tast.loc ~want:(Some ret) last :: rest) in (* Named after the function it was written in and numbered within it, which is the handler clause's rule and is stable for the same reason: a redefinition module emits the lifted functions belonging to the bodies it replaces, and an index into the whole program's list could not say which those were. *) let fname = (* Counted per *kind*, not over everything this function has lifted. A handler clause and an fn share one list, and a shared counter would renumber every fn in a function the moment a handler-bind was added above one — a rename for a body that did not change, in the names a redefinition module emits. Two counters, two stable sequences. *) let mine = List.filter (fun (l : Tast.fn) -> l.Tast.fparent = Some ctx.owner && String.length l.Tast.name >= 3 && String.sub l.Tast.name 0 3 = "fn/") ctx.env.lifted in Printf.sprintf "fn/%s/%d" ctx.owner (List.length mine) in ctx.env.lifted <- { Tast.name = fname; params = pts; slots = Array.of_list (List.rev fctx.slot_tys); snames = Array.of_list (List.rev fctx.slot_names); ret; body = fbody; fdefers = []; fparent = Some ctx.owner; floc = loc } :: ctx.env.lifted; expect loc ~want (mk loc (Types.Fn (pts, ret)) (Tast.FnAddr (Tast.Fnval fname))) (* A handler runs where the *signal* was, not where it was established, so it cannot be a branch in the function that wrote it: it is lifted into a function of its own and reached through a pointer. Which means it cannot see the establishing function's locals. Capturing them is a closure with an explicit environment — the non-escaping kind, captured by value onto this frame — and until that exists a reference to one is rejected by name rather than silently resolving to something else. Globals and the condition itself are in scope, which is enough for the accumulation case §1 is about. The body may not [return] either. The frames are pushed and popped around it, and an early exit would leave them on the stack pointing into a function that has gone. *) and check_handler_bind ctx ?want loc clauses body = ignore want; let frames = List.map (fun (c : Ast.hclause) -> let ty = resolve ctx.env c.Ast.hty in let name = match ty with | Types.Named n -> n | t -> fail c.Ast.hloc "a handler matches a struct type, not %s" (Types.to_string t) in (* Its own context: a fresh frame, an empty scope, and no way to reach the enclosing one. *) let hctx = { env = ctx.env; ret = Types.Unit; slots = 0; slot_tys = []; slot_names = []; scope = []; defers = []; outer = ctx.scope; outer_what = Some "a handler"; in_frames = None; loops = []; tail = false; in_defer = false; defer_ok = false; defer_block = "a nested form"; dead = []; borrow = false; owner = "" } in (* The condition crosses as a pointer, because the handler runs while the signalling frame is still alive and there is nothing to copy. What the clause binds is the condition itself, though, so the pointer is a hidden parameter and the name is a slot loaded from it — a handler that passed [c] to something expecting the struct would otherwise be handed an address. *) let pslot = fresh_slot hctx (Types.Ptr ty) in let cslot = bind hctx c.Ast.hname ty ~assignable:false in let hbody = map_lr (fun e -> check hctx e) c.Ast.hbody in let hbody = [ mk c.Ast.hloc Types.Unit (Tast.Let ([ (cslot, mk c.Ast.hloc ty (Tast.Deref (mk c.Ast.hloc (Types.Ptr ty) (Tast.Local pslot)))) ], hbody)) ] in (* Named after the function it came out of, and numbered within it: stable against an unrelated handler-bind being added elsewhere, which an index into the whole program's lifted list would not be. *) let fname = (* Per kind, for the reason [check_fn] gives: an fn lifted out of the same function must not shift this sequence. *) let mine = List.filter (fun (l : Tast.fn) -> l.Tast.fparent = Some ctx.owner && String.length l.Tast.name >= 8 && String.sub l.Tast.name 0 8 = "handler/") ctx.env.lifted in Printf.sprintf "handler/%s/%d/%s" ctx.owner (List.length mine) name in ctx.env.lifted <- { Tast.name = fname; params = [ Types.Ptr ty ]; slots = Array.of_list (List.rev hctx.slot_tys); snames = Array.of_list (List.rev hctx.slot_names); ret = Types.Unit; body = hbody; fdefers = []; fparent = Some ctx.owner; floc = c.Ast.hloc } :: ctx.env.lifted; { Tast.htype = type_id name; hfn = fname }) clauses in (* The flag is set on [ctx] itself and restored, not on a copy: [ctx.slots] and [ctx.slot_tys] are mutable, so a copy would allocate the body's slots into a record the function never sees again and the indices would collide. *) let saved = ctx.in_frames in ctx.in_frames <- Some "handler-bind"; let body = barrier ctx "a handler-bind" (fun () -> map_lr (fun e -> check ctx e) body) in ctx.in_frames <- saved; mk loc Types.Unit (Tast.Handled (frames, body)) (* (restart-case BODY (name [] BODY-1) ...) — spec-conditions.md §3 and §6. Unlike a handler, a clause runs *at* the restart-case, which is where it was written, so it is a branch in this function and sees this function's scope. What arrives from elsewhere is only the answer to "which clause": a transfer names the frame it is aimed at, and this form compares that against the frames it itself pushed. Every clause body and the body have the same type, and that is the type of the whole form — which is what makes the fall-through path visible in the source (§1): a restart-case in value position has to produce its type when no restart is invoked too. *) and check_restart_case ctx ?want loc body clauses = let saved = ctx.in_frames in ctx.in_frames <- Some "restart-case"; let tbody = barrier ctx "a restart-case" (fun () -> check ctx ?want body) in ctx.in_frames <- saved; (* With no expectation from outside, the body's own type is the expectation the clauses are checked against — unless it produced no value at all, in which case the first clause that does decides. *) let want = match want with | Some _ -> want | None -> if tbody.Tast.ty = Types.Never then None else Some tbody.Tast.ty in let ty = ref (match want with Some t -> Some t | None -> None) in let seen = ref [] in let clauses = map_lr (fun (c : Ast.rclause) -> (* Two clauses of one name would make §4's "the first frame offering the name" pick between them by an order nothing in the source shows. *) if List.mem c.Ast.rname !seen then fail c.Ast.rloc "this restart-case offers %s twice" c.Ast.rname; seen := c.Ast.rname :: !seen; (* §3's parameters. They are slots in *this* function — a clause runs here, not where the invoke was — and the invoker stores into a buffer this frame owns, because its own frame is gone by the time the clause body starts (§5). Bound like a function's parameters: visible only in the clause, and not assignable. *) let params, b = scoped ctx (fun () -> let params = List.map (fun (p : Ast.field) -> let ty = resolve ctx.env p.Ast.fty in (match ty with | Types.Unit | Types.Never -> fail p.Ast.floc "%s would be a restart parameter of type %s, which is \ not a value" p.Ast.fname (Types.to_string ty) | _ -> ()); (bind ctx p.Ast.fname ty ~assignable:false, ty)) c.Ast.rparams in (* Each is checked against what the form has settled on so far, so a clause that disagrees fails where it is written. The first one to produce a value is what settles it when nothing outside did. *) (params, (* The same barrier the body gets, and for the same reason: a clause runs after a transfer landed at this restart-case, with its frames still to be popped. *) barrier ctx "a restart-case" (fun () -> block ctx ?want:!ty c.Ast.rloc c.Ast.rbody))) in if !ty = None && b.Tast.ty <> Types.Never then ty := Some b.Tast.ty; let sg = restart_sig (List.map snd params) in { Tast.rname_id = type_id c.Ast.rname; rname = c.Ast.rname; rparams = params; rsig = sg; rsig_id = type_id sg; rbody = [ b ] }) clauses in let ty = match !ty with Some t -> t | None -> Types.Never in mk loc ty (Tast.RestartCase (clauses, tbody)) (* The forms of a [defer], checked in place and hung on the function. It emits nothing where it stands, so what is left behind is [unit]. *) and register_defer ctx loc forms = ctx.in_defer <- true; (* A barrier, for the reason [defer] itself exists: these forms are *copied* into every exit path of the function, where the loop they were written beside is not running. A loop written inside the defer is below the barrier and breaks out of itself perfectly well. *) let forms = barrier ctx "a defer" (fun () -> map_lr (fun d -> check ctx d) forms) in ctx.in_defer <- false; ctx.defers <- mk loc Types.Unit (Tast.Do forms) :: ctx.defers; unit_at loc (* [defer_ok] says whether *this* let has the function's extent. If it does, so does every form in its body, including a nested let — which is why the flag is handed to the body rather than consumed here. *) and check_let ctx ?(tail = false) ?want ?(defer_ok = false) loc bs body = scoped ctx (fun () -> let bs = map_lr (fun (b : Ast.binding) -> let want = Option.map (resolve ctx.env) b.Ast.bty in let v = check ctx ?want b.Ast.bval in (match v.Tast.ty with | Types.Unit | Types.Never -> fail b.Ast.bloc "%s would be bound to %s, which is not a value" b.Ast.bname (Types.to_string v.Tast.ty) | _ -> ()); (* Locals are assignable places; parameters are not. *) let slot = bind ctx b.Ast.bname v.Tast.ty ~assignable:true in (slot, v)) bs in (* After the bindings, because checking each of them withdrew it. *) ctx.tail <- tail; let body = block ctx ?want ~defer_ok loc body in mk loc body.Tast.ty (Tast.Let (bs, [ body ]))) (* (dotimes [i n] body...) is a counting loop, not a new IR node: bind [i] to 0 and the bound to a hidden slot — [n] is evaluated once, before the loop, so a body that changes it cannot change the trip count — then step [i] at the end of the body. [i] is not assignable, so the step below is the only writer. *) (* A loop body that moves a binding declared outside the loop is refused, and this is the one place the dead set cannot answer on its own: the second iteration would use what the first moved, and a set that is merged once at the end of the body sees one move, not two. So it is a rule rather than an inference, stated as one. *) and in_loop ctx ?label ?entry ?(fresh = []) f = let outer_slots = List.filter (fun s -> not (List.mem s fresh)) (List.map (fun (_, b) -> b.slot) ctx.scope) in let before = ctx.dead in (* The loop goes on the stack before the body is checked and comes off after, so a [break] inside it can see it and one outside it cannot. *) let loops = ctx.loops in (* [fresh] is a [loop]'s own names. They are bound before the entry is pushed — their initial values are evaluated once, outside — but [recur] writes every one of them on the way round, so the next iteration never sees what this one gave away and the rule below is not about them. *) ctx.loops <- (match entry with Some e -> e | None -> Lloop label) :: loops; (* Named so that a defer written in here is refused as "a loop body" rather than as a nested form: the reason is specific — it would fire once at function exit rather than once per iteration — and the message says it. *) let blocker = ctx.defer_block in ctx.defer_block <- "a loop body"; let r = f () in ctx.defer_block <- blocker; ctx.loops <- loops; List.iter (fun (slot, where) -> if (not (List.mem_assoc slot before)) && List.mem slot outer_slots then fail where "this moves a value that was bound outside the loop, so the next \ iteration would use what this one gave away. Move it out of the \ loop, or bind a fresh value inside it") ctx.dead; r (* Which loop a [break] or a [continue] means, as a count of loops outwards from the innermost — which is what [Tast.Break] carries and what [emit] indexes. Refuses three things, each by its own reason: nothing to break out of, a label naming no loop this form is inside, and a jump that would cross a barrier. *) and loop_target ctx loc verb label = let rec go depth = function | [] -> (match label with | None -> fail loc "%s is only allowed inside a loop" verb | Some l -> fail loc "no loop named :%s encloses this %s. A label names one of the loops \ this form is written inside — it is not a goto, so it cannot name a \ loop somewhere else" l verb) | Lloop name :: rest -> (match label with | None -> depth | Some l when name = Some l -> depth | Some _ -> go (depth + 1) rest) (* A [loop] answers with the value of its body. A jump out of one would have to produce that value from somewhere and there is nowhere, so it is a barrier like the others, named as what it is. A [while] written inside a loop sits below this entry and keeps its own break. *) | Lrecur _ :: _ -> (match label with | None -> fail loc "%s is not allowed here: the nearest loop is a (loop ...), which \ answers with the value of its body, so leaving it this way would \ have no value to give. Answer with the value, or use a while" verb | Some l -> fail loc "%s :%s would leave a (loop ...), which it may not: a loop answers \ with the value of its body and a jump out of one has no value to \ give" verb l) | Lbarrier what :: rest -> (* Crossing it would skip whatever the construct does on the way out — the handler or restart frames it pushed, or, for a defer, would jump to a loop that is not there on the path the forms were copied into. A loop nested inside the construct is below this entry and is never reached here, which is the whole point of the rule being relative. *) ignore rest; (match label with | None -> fail loc "%s is not allowed here: the nearest loop is outside %s, and leaving \ it that way would skip what %s does on the way out. Write the loop \ inside it, or leave with a value and test that after" verb what what | Some l -> fail loc "%s :%s would leave %s, which it may not: whatever %s does on the way \ out would be skipped. A break may only leave loops that are inside \ the same %s it is" verb l what what what) in go 0 ctx.loops and check_dotimes ctx ~want loc label name count body = let count = check ctx ~want:index_ty count in scoped ctx (fun () -> let i = bind ctx name index_ty ~assignable:false in let limit = fresh_slot ctx index_ty in let body = in_loop ctx ?label (fun () -> map_lr (fun b -> check ctx b) body) in let iv = mk loc index_ty (Tast.Local i) in let one = mk loc index_ty (Tast.Int (1L, Types.I32)) in let cond = mk loc Types.Bool (Tast.Prim (Tast.Lt, [ iv; mk loc index_ty (Tast.Local limit) ])) in let step = mk loc Types.Unit (Tast.Set (Tast.Plocal i, mk loc index_ty (Tast.Prim (Tast.Add, [ iv; one ])))) in let zero = mk loc index_ty (Tast.Int (0L, Types.I32)) in (* The step is the *latch* and not the last form of the body. Folded onto the body it would be skipped by a [continue], which branches past the rest of the body — so [i] would never advance and the loop would hang. That is the whole reason [Tast.While] carries a third list. *) let loop = mk loc Types.Unit (Tast.While (cond, body, [ step ])) in expect loc ~want (mk loc Types.Unit (Tast.Let ([ (i, zero); (limit, count) ], [ loop ])))) (* ── (loop [...] ...) and (recur ...) ─────────────────────────────────── A loop is a [let] over its names, a [While] whose condition is [true], and two jumps: [recur] rebinds every name and continues, and falling off the end of the body breaks. Nothing new reaches the backend, which is the whole argument for [recur] over tail calls — the machinery is the one [while] and the labelled [break]/[continue] already needed. **The value.** A loop answers with the value of its body, so the result is written into a slot of its own on the way out and read after the loop. A body that is [Unit] needs no slot, and a body that is [Never] — one that only ever recurs or returns — needs neither a slot nor the break, because nothing falls off the end of it. **Why [Set] of a [Never] body is safe.** [emit] closes a block at its terminator and drops what follows ([ins] checks [f.live]), so when the body ends in a jump the store is simply never written. The one ordering that matters is inside [Tast.Set]: the place is resolved before the value, and a local's place is an address with no instruction behind it. **Why the invented [While] may carry jumps.** [tast.ml] says a [While] the checker invents contains none, because the depths it would carry were minted against a stack it is not on. This one is different and the difference is the licence: it is pushed on [ctx.loops] like any other, so the [Break 0] below and every [continue] a [recur] mints count from the same stack [emit] indexes. *) and check_loop ctx ?want loc bs body = scoped ctx (fun () -> (* Each initial value is evaluated once, before the loop, exactly as a [let]'s is and as [dotimes]'s bound is. *) let inits = map_lr (fun (n, v) -> let v = check ctx v in (match v.Tast.ty with | Types.Unit | Types.Never -> fail v.Tast.loc "%s would be bound to %s, which is not a value" n (Types.to_string v.Tast.ty) | _ -> ()); (n, v)) bs in let binds = List.map (fun (n, v) -> (bind ctx n v.Tast.ty ~assignable:true, v)) inits in let names = List.map (fun (slot, v) -> (slot, v.Tast.ty)) binds in (* The singleton is [in_loop]'s doing: it sits in this recursive group and is therefore monomorphic, and every other caller hands it a list. *) let tbody = match in_loop ctx ~entry:(Lrecur names) ~fresh:(List.map fst binds) (fun () -> [ scoped ctx (fun () -> (* The body's last form is the loop's tail, which is the only place a [recur] may stand. [block] distributes it. *) ctx.tail <- true; block ctx ?want loc body) ]) with | [ b ] -> b | _ -> assert false in let ty = tbody.Tast.ty in let yes = mk loc Types.Bool (Tast.Bool true) in let leave = mk loc Types.Never (Tast.Break 0) in let inner, result = if ty = Types.Never then ([ tbody ], None) else if ty = Types.Unit then ([ tbody; leave ], None) else let r = fresh_slot ctx ty in ([ mk loc Types.Unit (Tast.Set (Tast.Plocal r, tbody)); leave ], Some r) in let loop = mk loc Types.Unit (Tast.While (yes, inner, [])) in match result with | None -> expect loc ~want (mk loc ty (Tast.Let (binds, [ loop ]))) | Some r -> expect loc ~want (mk loc ty (Tast.Let (binds @ [ (r, mk loc ty (Tast.Zero ty)) ], [ loop; mk loc ty (Tast.Local r) ])))) (* Which loop a [recur] means, and what it has to rebind. The same walk [break] and [continue] make, over the same stack and refusing on the same barriers — [recur] asks "may this jump cross that" and gets the answer that was already settled, not a second mechanism. *) and recur_target ctx loc = let rec go depth = function | [] -> fail loc "recur is only allowed inside a (loop ...). There are no tail calls in \ this compiler, so a function cannot recur into itself and two \ functions cannot recur into each other — write the repetition as a \ loop with a recur in its tail" | Lrecur names :: _ -> (depth, names) (* Unreachable while the tail rule holds — a loop body is not a tail position, so no [recur] is ever written inside one — but the depth is counted rather than assumed, because it is what [emit] indexes. *) | Lloop _ :: rest -> go (depth + 1) rest | Lbarrier what :: _ -> fail loc "recur would leave %s, which it may not: whatever %s does on the way \ out would be skipped. Write the loop inside it, or leave with a value \ and test that after" what what in go 0 ctx.loops and check_recur ctx ~tail loc args = let depth, names = recur_target ctx loc in (* Checked, which is the whole of why this is better than a silent TCO: a recur that is not in tail position is a compile error here, where under tail calls it would have been a stack overflow at run time. *) if not tail then fail loc "recur must be in the tail position of its loop — the last thing the \ body does, or the last thing in an if, match or let arm that is itself \ in the tail. Here something would still have to run afterwards, and a \ recur is a jump back to the top, not a call that returns"; let want = List.length names and got = List.length args in if want <> got then fail loc "this loop binds %d name%s and this recur passes %d" want (if want = 1 then "" else "s") got; let vals = List.map2 (fun a (_, ty) -> check ctx ~want:ty a) args names in (* Every name is rebound at once. The new values go into temporaries first, so that (recur y x) swaps rather than writing y over x and then reading it back — the same reason Clojure's recur is simultaneous. *) let temps = List.map2 (fun v (_, ty) -> (fresh_slot ctx ty, v)) vals names in let sets = List.map2 (fun (t, _) (slot, ty) -> mk loc Types.Unit (Tast.Set (Tast.Plocal slot, mk loc ty (Tast.Local t)))) temps names in mk loc Types.Never (Tast.Let (temps, sets @ [ mk loc Types.Never (Tast.Continue depth) ])) and check_if ctx ?(tail = false) ?want loc c t e = let c = check ctx ~want:Types.Bool c in (* Both arms are the tail, and a one-armed [if] counts: [(when c (recur ...))] is how nearly every loop is written, and the branch is still the last thing the body does. *) let in_tail f = ctx.tail <- tail; f () in match e with | None -> (* A one-armed if produces Unit whatever the branch evaluates to: there is no value on the missing side. `when` desugars to this. *) let t = branch ctx (fun () -> in_tail (fun () -> check ctx t)) in expect loc ~want (mk loc Types.Unit (Tast.If (c, t, unit_at loc))) | Some e -> (* Both arms start from the same dead set and the data type survives: moving in one arm only still kills the binding afterwards, and moving in both — which is legal and common — is not reported twice. A flat set would have refused [(if c (free v) (free v))] and allowed the use after a one-armed move, which are the two ways to be wrong here. *) let before = ctx.dead in let t = branch ctx (fun () -> in_tail (fun () -> check ctx ?want t)) in let after_then = ctx.dead in ctx.dead <- before; (* With no expectation the then-branch supplies one for the else-branch, unless it diverges, in which case the else-branch decides. *) let ewant = match want with | Some _ -> want | None -> if t.Tast.ty = Types.Never then None else Some t.Tast.ty in let e = branch ctx (fun () -> in_tail (fun () -> check ctx ?want:ewant e)) in ctx.dead <- after_then @ List.filter (fun (k, _) -> not (List.mem_assoc k after_then)) ctx.dead; let ty = if t.Tast.ty = Types.Never then e.Tast.ty else if e.Tast.ty = Types.Never then t.Tast.ty else if Types.equal t.Tast.ty e.Tast.ty then t.Tast.ty else fail loc "the branches of this if have different types: %s and %s" (Types.to_string t.Tast.ty) (Types.to_string e.Tast.ty) in mk loc ty (Tast.If (c, t, e)) (* A record-shaped literal: one form for both, because [(Name {.f v})] is the same syntax whether [Name] is a struct or a data type case, and the two differ only in what is built at the end. Deciding here rather than in the parser is what lets the decision be made against the tables, exactly. *) and check_struct ctx ~want loc name kvs = match Hashtbl.find_opt ctx.env.structs name with | None when Hashtbl.mem ctx.env.unions name -> check_union ctx ~want loc name kvs | None -> (match Hashtbl.find_opt ctx.env.cases name with (* The full spelling [U.C], which is how a data type value is written. Checked before the diagnostics below, since the bare-name entry in the same table is only ever a hint. *) | Some (dname, c) when String.contains name '.' -> check_case ctx ~want loc dname c kvs (* A bare case name. This is the bug NEXT.md listed under "Bugs found and not yet fixed": [(A {.x 1})] on a case of a data type reported "unknown struct A", because nothing in [env] could tell a case name from a misspelling. It can now, so it says what was meant. *) | Some (dname, c) -> fail loc "%s is a case of the data type %s, not a struct — a data type value names \ both, as (%s.%s {.field value ...})" name dname dname c.Tast.vname | None -> if Hashtbl.mem ctx.env.datas name then fail loc "%s is a data type, and a data type value names the case as well as the \ type — write (%s.%s {.field value ...}) for one of %s" name name (first_case_name ctx.env name) (case_list ctx.env name) else Loc.failk "check/unknown-struct" loc ~notes:(declared_note ctx.env name) "unknown struct %s" name) | Some s -> let seen = Hashtbl.create 8 in List.iter (fun (k, (v : Ast.expr)) -> (match Hashtbl.find_opt seen k with | Some (first : Ast.expr) -> Loc.failk "check/duplicate-field" v.Ast.loc ~notes:[ Loc.note first.Ast.loc (k ^ " is given here first") ] "field %s is given twice" k | None -> ()); if Tast.field_index s k = None then Loc.failk "check/unknown-field" v.Ast.loc ~notes:(declared_note ctx.env name) "%s has no field %s" name k; Hashtbl.add seen k v) kvs; (* Omitted fields are zeroed — ZII, the same rule as a declaration with no initialiser (plan.org, Data model). Every field is present from here on, in declaration order, so no backend has to know about omission. *) let fields = map_lr (fun (f : Tast.field) -> match Hashtbl.find_opt seen f.Tast.fname with | Some v -> check ctx ~want:f.Tast.fty v | None -> mk loc f.Tast.fty (Tast.Zero f.Tast.fty)) s.Tast.fields in expect loc ~want (mk loc (Types.Named name) (Tast.Make (name, fields))) (* [(U {.member v})] — an untagged union value. At most one member, because the members are one storage: giving two would be writing two values over each other and the result would be whichever the compiler happened to store last. That is a real question with no answer, so it is refused rather than ordered. Giving none is the ordinary ZII value and is all-bytes-zero, the same as a struct with every field omitted. The one member is lowered here into a zeroed temporary and a store, rather than into a node of its own. A union value *is* a store into overlaid storage — [Set] over [Pfield] is exactly that operation and every backend already has it — so a [MakeUnion] node would have been the same three instructions written a fourth and fifth time, in each backend, with the layout rule spelled out again in each. Nothing downstream learns anything new from this form. *) and check_union ctx ~want loc name kvs = let u = Hashtbl.find ctx.env.unions name in List.iter (fun (k, (v : Ast.expr)) -> if Tast.field_index u k = None then Loc.failk "check/unknown-field" v.Ast.loc ~notes:(declared_note ctx.env name) "%s has no member %s" name k) kvs; let seen = Hashtbl.create 8 in List.iter (fun (k, (v : Ast.expr)) -> (* Before the two-member refusal below, so [(U {.i 1 .i 2})] is told it named one member twice rather than that [i] and [i] are the same bytes — which is true and useless. Same words and same note as the struct path, because it is the same mistake. *) (match Hashtbl.find_opt seen k with | Some (first : Ast.expr) -> Loc.failk "check/duplicate-field" v.Ast.loc ~notes:[ Loc.note first.Ast.loc (k ^ " is given here first") ] "member %s is given twice" k | None -> ()); Hashtbl.add seen k v) kvs; (match kvs with | (a, _) :: (b, (second : Ast.expr)) :: _ -> Loc.failk "check/union-two-members" second.Ast.loc "%s is a union, so %s and %s are the same bytes and only one of them \ can be written — give the one this value is, and read the other \ member when you want to see those bytes that way" name a b | _ -> ()); match kvs with (* The two-member case left above, so this sees one or none. *) | _ :: _ :: _ -> assert false | [] -> expect loc ~want (mk loc (Types.Named name) (Tast.Zero (Types.Named name))) | [ (k, v) ] -> let i = Option.get (Tast.field_index u k) in let fty = (List.nth u.Tast.fields i).Tast.fty in let v = check ctx ~want:fty v in let slot = fresh_slot ctx (Types.Named name) in let here = mk loc (Types.Named name) (Tast.Local slot) in expect loc ~want (mk loc (Types.Named name) (Tast.Let ([ (slot, mk loc (Types.Named name) (Tast.Zero (Types.Named name))) ], [ mk loc Types.Unit (Tast.Set (Tast.Pfield (here, i), v)); here ]))) (* The cases of a data type, as written, for a message that has to name them. *) and case_list env dname = match Hashtbl.find_opt env.datas dname with | None -> "its cases" | Some u -> String.concat ", " (List.map (fun (c : Tast.variant) -> dname ^ "." ^ c.Tast.vname) u.Tast.cases) and first_case_name env dname = match Hashtbl.find_opt env.datas dname with | Some { Tast.cases = c :: _; _ } -> c.Tast.vname | _ -> "Case" (* [(U.C {.f v ...})]. The fields are checked and filled in exactly as a struct's are — same ZII, same duplicate and unknown-field refusals — and the only difference is the node at the end and the type it carries. *) and check_case ctx ~want loc dname (c : Tast.variant) kvs = let full = dname ^ "." ^ c.Tast.vname in let seen = Hashtbl.create 8 in List.iter (fun (k, (v : Ast.expr)) -> (match Hashtbl.find_opt seen k with | Some (first : Ast.expr) -> Loc.failk "check/duplicate-field" v.Ast.loc ~notes:[ Loc.note first.Ast.loc (k ^ " is given here first") ] "field %s is given twice" k | None -> ()); if Tast.vfield_index c k = None then Loc.failk "check/unknown-field" v.Ast.loc ~notes:(declared_note ctx.env dname) "%s has no field %s" full k; Hashtbl.add seen k v) kvs; let fields = map_lr (fun (f : Tast.field) -> match Hashtbl.find_opt seen f.Tast.fname with | Some v -> check ctx ~want:f.Tast.fty v | None -> mk loc f.Tast.fty (Tast.Zero f.Tast.fty)) c.Tast.vfields in expect loc ~want (mk loc (Types.Named dname) (Tast.MakeCase (dname, c.Tast.vname, fields))) and check_arr ctx ~want loc items = let elem_want = match want with | Some (Types.Array (_, t)) -> Some t | Some (Types.Slice t) -> Some t | _ -> None in let items = map_lr (fun i -> check ctx ?want:elem_want i) items in let n = Int64.of_int (List.length items) in let elem = match elem_want, items with | Some t, _ -> t | None, first :: _ -> first.Tast.ty | None, [] -> fail loc "an empty array literal needs a type — annotate the binding" in List.iter (fun (i : Tast.expr) -> if not (Types.fits ~expected:elem ~actual:i.Tast.ty) then fail i.Tast.loc "this array's elements are %s, but this one is %s" (Types.to_string elem) (Types.to_string i.Tast.ty)) items; (match want with | Some (Types.Array (m, _)) when not (Int64.equal m n) -> fail loc "expected %Ld elements, found %Ld" m n | _ -> ()); (* [n T] and [T] are distinct in type and in ownership (spec-memory.md), so an array literal does not satisfy a slice expectation. *) expect loc ~want (mk loc (Types.Array (n, elem)) (Tast.Arr items)) and check_match ctx ?(tail = false) ?want loc scrutinee arms = let s = check ctx scrutinee in (* What the arms are alternatives over. An [Option] is a two-case data type wearing a special coat, so the two shapes below are the same shape: a set of case names, an arity and a payload type per case, and a tag. Keeping them apart here rather than desugaring [Option] into a declared data type is deliberate — [Option] is generic and no declared data type is, so the coat is the part that cannot yet be taken off. *) let subject = match s.Tast.ty with | Types.Option t -> `Option t | Types.Named n when Hashtbl.mem ctx.env.datas n -> `Data (Hashtbl.find ctx.env.datas n) (* An enum is the one scrutinee that is not a milestone away: it is an i32 at run time and its members are all known, so the arms would be a chain of [=] with an exhaustiveness check over [env.enums] — a desugaring, not a new IR node. What blocks it is upstream of here: a keyword has no case in [Ast.pattern], and [lib/load.ml] matches that type exhaustively, so the variant cannot be added. Said as itself rather than folded into the milestone answer below, because the milestone is not the reason. *) | Types.Enum n -> fail loc "match over the enum %s is not implemented — the lowering is a chain \ of (= k :member), but a keyword has no case in the pattern type yet. \ Use cond" n (* An untagged union has nothing for the arms to be alternatives over. This is not a milestone and not a missing lowering: [match] reads a tag and decides, and the absence of a tag is the whole definition of this type. Said by name, because the two kinds of union are one keyword apart in the source and someone will write it. *) | Types.Named n when Hashtbl.mem ctx.env.unions n -> fail loc "%s is a union, and there is nothing in one to match on: its members \ overlay the same bytes and nothing records which was written. Read \ the member you mean with (.member u), or keep a tag of your own \ beside it in a struct and match on that. A tagged alternative is \ what defdata is" n | other -> fail loc "match works on an Option or a data type, not on %s" (Types.to_string other) in (* Which case each arm names, and the type of each name it binds. This is the whole of what differs between the two subjects; everything below it is shared. *) let resolve_pat (a : Ast.arm) = match subject, a.Ast.pat with | _, Ast.Pwild -> None, [] | `Option elem, Ast.Pctor ("Some", [ x ]) -> Some "Some", [ (x, elem) ] | `Option _, Ast.Pctor ("Some", _) -> fail a.Ast.aloc "the Some pattern binds exactly one name" | `Option _, Ast.Pctor ("None", []) -> Some "None", [] | `Option _, Ast.Pctor ("None", _) -> fail a.Ast.aloc "None binds no names" | `Option _, Ast.Pctor (c, _) -> fail a.Ast.aloc "%s is not a case of Option — the cases are Some and None" c | `Data u, Ast.Pctor (c, names) -> (* A pattern names the case bare: the scrutinee's type already says which data type, so [(Node l r)] is unambiguous even where two data types share the case name. The qualified spelling is accepted too, since that is how the value was written and writing it again should not be an error. *) let bare = let full = u.Tast.dname ^ "." in let n = String.length full in if String.length c > n && String.sub c 0 n = full then String.sub c n (String.length c - n) else c in (match Tast.case_index u bare with | None -> fail a.Ast.aloc "%s is not a case of %s — the cases are %s" c u.Tast.dname (String.concat ", " (List.map (fun (v : Tast.variant) -> v.Tast.vname) u.Tast.cases)) | Some (_, v) -> (* Positional, in declaration order, and all of them or none: a pattern that bound some of a case's fields would be silently reading the wrong one after a field is inserted. Refused with the count, which is the thing that is wrong. *) if List.length names <> List.length v.Tast.vfields then fail a.Ast.aloc "%s.%s has %d field%s, and this pattern binds %d — a case pattern \ binds every field, in declaration order (%s)" u.Tast.dname bare (List.length v.Tast.vfields) (if List.length v.Tast.vfields = 1 then "" else "s") (List.length names) (String.concat " " (List.map (fun (f : Tast.field) -> f.Tast.fname) v.Tast.vfields)); Some bare, List.map2 (fun n (f : Tast.field) -> (n, f.Tast.fty)) names v.Tast.vfields) in let want = ref want in let seen = Hashtbl.create 8 in let saw_wild = ref false in (* The same rule as [if], and for the same reason: the arms are alternatives, so each is checked from the state before the match and the data type of what they moved survives the join. Checked in sequence against one mutating set they would report the second arm's (free v) as a use after the first arm's move, which is a legal program refused. *) let before = ctx.dead in let joined = ref [] in let arms = map_lr (fun (a : Ast.arm) -> let ctor, binds = resolve_pat a in (match ctor with | None -> saw_wild := true | Some c -> if Hashtbl.mem seen c then fail a.Ast.aloc "this match has two %s arms" c; Hashtbl.add seen c ()); ctx.dead <- before; let arm = branch ctx (fun () -> let binds = List.map (fun (n, ty) -> bind ctx n ty ~assignable:false) binds in (* Every arm is the tail, exactly as an [if]'s two arms are. Restored here because checking the scrutinee withdrew it. *) ctx.tail <- tail; let body = block ctx ?want:!want a.Ast.aloc a.Ast.body in if !want = None && body.Tast.ty <> Types.Never then want := Some body.Tast.ty; { Tast.acase = ctor; binds; abody = [ body ] }) in joined := !joined @ List.filter (fun (k, _) -> not (List.mem_assoc k !joined)) ctx.dead; arm) arms in ctx.dead <- !joined; (* Exhaustiveness is refused, not defaulted. A match that silently fell through would have to produce a value of the match's type out of nothing, and there is no such value for most types; and the case a data type grows tomorrow is exactly the one a reader wants to be told about today. A [_] arm is the way to say "the rest", written where it can be seen. *) let missing = match subject with | `Option _ -> List.filter (fun c -> not (Hashtbl.mem seen c)) [ "Some"; "None" ] | `Data u -> List.filter_map (fun (c : Tast.variant) -> if Hashtbl.mem seen c.Tast.vname then None else Some (u.Tast.dname ^ "." ^ c.Tast.vname)) u.Tast.cases in if not !saw_wild && missing <> [] then (* The data type's declaration, because that is where the case list this match failed to cover actually lives, and because adding a case there is what makes a match non-exhaustive in the first place. *) Loc.failk "check/non-exhaustive-match" loc ~notes:(match subject with `Data u -> declared_note ctx.env u.Tast.dname | _ -> []) "this match is not exhaustive — %s %s no arm. Add %s, or a _ arm for \ the rest" (String.concat ", " missing) (if List.length missing = 1 then "has" else "have") (if List.length missing = 1 then "it" else "them"); let ty = match !want with Some t -> t | None -> Types.Never in mk loc ty (Tast.Match (s, arms)) (* ── Places ────────────────────────────────────────────────────────── *) (* The fields a name has, whether it is a struct or an untagged union. The two are one record and differ only in what the offsets come out as, which is a question for the layout and not for this — so [.x] is one path and not two, and a union member is read with the accessor everything else is read with. That is the whole of what makes punning ordinary code. *) and fields_named env n : Tast.structure option = match Hashtbl.find_opt env.structs n with | Some s -> Some s | None -> Hashtbl.find_opt env.unions n (* The target of [.field] is a struct or an untagged union, or one level of pointer to one. The auto-deref is inserted here as a real node, so no backend re-derives it. *) and struct_target ctx (target : Ast.expr) : Tast.expr * string = let t = check ctx target in let has n = fields_named ctx.env n <> None in match t.Tast.ty with | Types.Named n when has n -> t, n | Types.Ptr (Types.Named n) when has n -> mk t.Tast.loc (Types.Named n) (Tast.Deref t), n (* A data type's fields belong to one case, and which case it is holding is only known after the tag has been read. [.field] would have to be a read that might be reading something else, so it is not one: [match] is how a data type is opened, and it binds the fields it has proved are there. *) | (Types.Named n | Types.Ptr (Types.Named n)) when Hashtbl.mem ctx.env.datas n -> fail target.Ast.loc "%s is a data type, and a data type's fields belong to a case — which \ one it is holding is what the tag says, so they are reached by (match ...), \ whose arms bind the fields of the case they matched" n | other -> fail target.Ast.loc "%s is not a struct, so it has no fields" (Types.to_string other) and check_place ctx loc (p : Ast.place) : Tast.place * Types.t = match p with | Ast.Pvar name -> (match lookup ctx name with | Some b -> if not b.assignable then fail loc "%s is a parameter, and parameters are not assignable places \ (spec-memory.md) — bind a local with let" name; Tast.Plocal b.slot, b.bty | None -> match Hashtbl.find_opt ctx.env.globals name with | Some (_, true) -> fail loc "%s is a constant" name | Some (ty, false) -> Tast.Pglobal name, ty | None -> captured ctx loc name; Loc.failk "check/unknown-name" loc "unknown name %s" name) | Ast.Pfield (target, name) -> let target, sname = struct_target ctx target in let s = Option.get (fields_named ctx.env sname) in (match Tast.field_index s name with | None -> Loc.failk "check/unknown-field" loc ~notes:(declared_note ctx.env sname) "%s has no field %s" sname name | Some i -> Tast.Pfield (target, i), (List.nth s.Tast.fields i).Tast.fty) | Ast.Pindex (target, idx) -> let target = borrowed ctx target (fun () -> check ctx target) in (match target.Tast.ty with (* The same bounds and epoch check the value form gets, through the same helper: an element of a Vec is a place because a Vec element is assignable, and a set that skipped the checks would be the asymmetry [nth] was removed for. *) | Types.Vec _ -> let p, ty = vec_at ctx loc target idx in Tast.Pderef p, ty | _ -> let idx, ty = indexed ctx target idx in Tast.Pindex (target, idx), ty) | Ast.Pderef target -> let target = check ctx target in (match target.Tast.ty with | Types.Ptr t -> Tast.Pderef target, t | other -> fail loc "deref takes a (Ptr T), found %s" (Types.to_string other)) (* An index or a slice bound that is a literal is known now, so it is an error now rather than a trap later. Only literals: a [defconst] is a global in the typed IR, not a folded constant, so [(at arr size)] still traps at runtime — which is what the emitted bounds check is for. A negative literal is wrong whatever the target, but a length is static only for [n T]. *) and static_index loc (ty : Types.t) ~past_end what k = if k < 0L then fail loc "%s %Ld is negative — indices count from 0" what k; match ty with (* [past_end] is the difference between an index and a slice bound: the last valid index is len - 1, but a slice may end at len. *) | Types.Array (n, _) when if past_end then k > n else k >= n -> fail loc "%s %Ld is out of bounds for length %Ld" what k n | _ -> () (* The literal value of a checked expression, if it has one. *) and literal (e : Tast.expr) = match e.Tast.e with Tast.Int (k, _) -> Some k | _ -> None (* An index is [i32] internally, but a *narrower* integer may be written as one: indexing is not arithmetic on the value, so there is nothing for a visible cast to warn about, and requiring (i32 c) at every subscript would be noise. A u32 is included because it cannot lose a value the bounds check would then miss — anything above 2^31 truncates to a negative i32, which the unsigned comparison rejects. i64 and u64 are not: 2^32 + 5 truncates to 5 and would read the wrong element with no trap at all, so those need the cast written out. *) and index_expr ctx (e : Ast.expr) = (* No [want]: an expectation of [i32] would reject a [u32] index outright, before there is anything here to convert. An untyped literal still defaults to [i32] on its own. *) let v = check ctx e in match v.Tast.ty with | Types.Int Types.I32 -> v | Types.Int k when Types.bits k <= 32 -> { v with Tast.ty = index_ty; Tast.e = Tast.Prim (Tast.Cast index_ty, [ v ]) } | Types.Int k -> fail e.Ast.loc "an index is an i32, and %s is wider — write (i32 …), because a value \ that does not fit truncates to one that does and would read the wrong \ element without tripping the bounds check" (Types.ikind_name k) | other -> fail e.Ast.loc "an index is an integer, found %s" (Types.to_string other) (* [(at a i)] and [(at grid row col)]: one index per dimension. *) and indexed ctx (target : Tast.expr) (idx : Ast.expr list) = let rec go ty = function | [] -> [], ty | i :: rest -> let elem = match ty with | Types.Array (_, t) | Types.Slice t -> t | other -> fail i.Ast.loc "%s cannot be indexed" (Types.to_string other) in let loc = i.Ast.loc in let i = index_expr ctx i in (match literal i with | Some k -> static_index loc ty ~past_end:false "index" k | None -> ()); let rest, ty = go elem rest in i :: rest, ty in go target.Tast.ty idx (* ── Calls ─────────────────────────────────────────────────────────── *) and check_call ctx ~want loc (head : Ast.expr) (args : Ast.expr list) = match head.Ast.e with | Ast.Var name -> named_call ctx ~want loc name args (* A computed head: ((choose k) 3). The head is an ordinary expression and the only thing asked of it is that it be a function. *) | _ -> call_value ctx ~want loc (check ctx head) args (* The indirect call, once the callee is checked. Shared by the computed head above and by a name that resolved to a local or a parameter of function type, which is the shape every caller of [map] has. *) and call_value ctx ~want loc (callee : Tast.expr) args = match callee.Tast.ty with | Types.Fn (params, ret) -> if List.length args <> List.length params then fail loc "this function value takes %d argument%s, given %d" (List.length params) (if List.length params = 1 then "" else "s") (List.length args); let args = map2_lr (fun p a -> check ctx ~want:p a) params args in expect loc ~want (mk loc ret (Tast.CallPtr (callee, args))) | other -> fail loc "this is a %s and not a function, so it cannot be called" (Types.to_string other) and arity loc name n args = if List.length args <> n then fail loc "%s takes %d argument%s, given %d" name n (if n = 1 then "" else "s") (List.length args) (* The operators that fold: [+ - * /], [min]/[max] and the three bitwise combining operators all take two operands or more, and mean the same thing applied left to right. [%] and the shifts are not in that set — a chain of remainders or of shifts has no reading a reader would agree on in advance, so there the arity error is the useful answer. Two is the floor, and the two missing cases are refused rather than invented. Zero operands would have to mean an identity element, 0 for + and 1 for *, and a sum with no terms in it is a typo far more often than it is an intent. One operand would have to mean negation for [-] and reciprocal for [/], and this language has no unary minus anywhere: the prelude writes every negation as [(- 0 n)] or [(- 0.0 x)], and [(- x)] meaning something else than the [-] two lines above it is a rule a reader has to carry rather than see. *) and fold_arity loc name args = match args with | _ :: _ :: _ -> () | [ _ ] when String.equal name "-" -> fail loc "- takes two arguments or more, given 1 — there is no unary minus; \ write (- 0 x) to negate, which is what the prelude does" | [ _ ] when String.equal name "/" -> fail loc "/ takes two arguments or more, given 1 — there is no reciprocal; \ write (/ 1.0 x)" | _ -> fail loc "%s takes two arguments or more, given %d" name (List.length args) (* The first two operands decide the type — [binary] picks which of them is allowed to, and that decision is not re-made per pair — and every operand after them is checked against it. *) and fold_left_prim ctx ~want loc name p ok what args = let x, y, rest = match args with x :: y :: rest -> x, y, rest | _ -> assert false in let a, b = binary ctx name loc ~want:(numeric_want want) [ x; y ] in unconstrained ctx.env loc name ~needs:"numeric?" a.Tast.ty; (* Past [unconstrained] a variable here is one the [where] clause admitted, so the concrete predicate below has nothing to say about it — it is answered again, per copy, at the instantiation. *) if not (ok a.Tast.ty || generic_ty a.Tast.ty) then fail loc "%s takes %s, found %s" name what (Types.to_string a.Tast.ty); let ty = a.Tast.ty in let acc = List.fold_left (fun acc arg -> mk loc ty (Tast.Prim (p, [ acc; check ctx ~want:ty arg ]))) (mk loc ty (Tast.Prim (p, [ a; b ]))) rest in expect loc ~want acc (* ── Allocation failure, spec-memory.md ──────────────────────────────── No allocating operation returns an error and none can fail silently. When the allocator cannot satisfy a request the operation signals (StorageExhausted {.bytes n .align a .allocator id}) with [error] — whose type is Never — inside a [restart-case] offering [retry]. That is one rule over every allocating operation, which is what keeps [push] and [reserve] at Unit, [clone] at the container, and no signature anywhere growing a Result. Odin's [append] returns an ignorable Allocator_Error and its type-erased path returns the old length on a failed reserve; an append that appends nothing and says nothing is the outcome this rule exists to make impossible. It is *compiler-emitted at the point of failure*, which spec-memory.md names as the exception to plan.org's "restarts go at the resync point, once": a restart established at a parser's top-level loop cannot re-attempt an allocation, and only the allocation site can. The shape is built out of nodes that already exist — a while, a restart-case and an error — so the backend learns nothing new about allocation: (let [ok false] (while (not ok) (restart-case (do (set ok ATTEMPT) (if (not ok) (error (StorageExhausted {...})))) (retry [])))) A handler that frees something, releases a scratch region or grows the arena and then invokes [retry] lands in the clause, the clause falls through, and the while re-tests and re-attempts the *same* request. With nothing handling it, [error] stops the program on the frame that erred, as §2 says. [attempt] must be a call that can be repeated: every argument to it is bound to a slot before the loop, so a retry does not re-evaluate the element expression a push was given. *) and alloc_guard ctx loc (attempt : Tast.expr) = let ok = fresh_slot ctx Types.Bool in let okv = mk loc Types.Bool (Tast.Local ok) in let notok () = mk loc Types.Bool (Tast.Prim (Tast.Not, [ okv ])) in let i8 n = mk loc (Types.Int Types.I8) (Tast.Int (n, Types.I8)) in (* The runtime answers 1 or 0 and never reports failure any other way. *) let attempt = mk loc Types.Bool (Tast.Prim (Tast.Ne, [ attempt; i8 0L ])) in (* A value struct on the signalling frame's stack, with fixed numeric fields and no rendered message: formatting would allocate, and this is the one path that must not. Rendering happens in the handler or the break loop, where a working allocator is known. *) let cond = mk loc (Types.Named "StorageExhausted") (Tast.Make ("StorageExhausted", [ rt loc (Types.Int Types.I64) "flan_alloc_fail_bytes" []; rt loc (Types.Int Types.I64) "flan_alloc_fail_align" []; rt loc (Types.Int Types.I64) "flan_alloc_fail_id" [] ])) in let signal = mk loc Types.Never (Tast.Signal (Tast.Serror, type_id "StorageExhausted", cond)) in let attempt_then_signal = mk loc Types.Unit (Tast.Do [ mk loc Types.Unit (Tast.Set (Tast.Plocal ok, attempt)); mk loc Types.Unit (Tast.If (notok (), signal, unit_at loc)) ]) in let clause = (* Compiler-emitted, so it takes no parameters: nothing outside can hand this one a value. [rsig] is therefore the empty signature, and its hash the same one a written [(retry [] ...)] gets — the two must agree, since an [invoke-restart] cannot tell them apart. *) let sg = restart_sig [] in { Tast.rname_id = type_id "retry"; rname = "retry"; rparams = []; rsig = sg; rsig_id = type_id sg; rbody = [ unit_at loc ] } in let body = mk loc Types.Unit (Tast.RestartCase ([ clause ], attempt_then_signal)) in mk loc Types.Unit (Tast.Let ([ (ok, mk loc Types.Bool (Tast.Bool false)) ], [ mk loc Types.Unit (Tast.While (notok (), [ body ], [])) ])) (* ── File failure, decisions 2 and 5 ─────────────────────────────────── The same shape [alloc_guard] has, for the same reason and out of the same nodes: the operation signals inside a [restart-case] it establishes itself, so nothing anywhere grows a Result and neither [slurp] nor [barf] can fail silently. Compiler-emitted at the point of failure, which spec-memory.md already names as the exception to plan.org's "restarts go at the resync point, once" — a restart at an outer loop cannot re-open a file. Two restarts, and they are the textbook pair Common Lisp establishes for a file-error: retry the file may be there now — the handler made a directory, mounted something, or waited. use-value [p string] try this other path instead. [use-value]'s parameter *is* the path slot, so the clause body is [unit]: emit.ml's [bind_params] stores the invoker's argument straight into the slot the attempt reads, the clause falls through, and the while re-tests and re-attempts against the new path. Typed restarts landed this session and this is the first thing the compiler itself emits one for. [attempt] must be repeatable, so the path is a slot read at each turn of the loop rather than an expression re-evaluated. *) and file_guard ctx loc ~path_slot ~op mk_steps = let ok = fresh_slot ctx Types.Bool in let okv = mk loc Types.Bool (Tast.Local ok) in let notok () = mk loc Types.Bool (Tast.Prim (Tast.Not, [ okv ])) in let i8 n = mk loc (Types.Int Types.I8) (Tast.Int (n, Types.I8)) in (* Fixed fields and no rendered message, exactly as StorageExhausted: the condition is built on the failing frame's stack and formatting is the handler's job. [path] is whatever the attempt last used, so a handler that supplied one through [use-value] sees the path that actually failed. *) let cond = mk loc (Types.Named "FileError") (Tast.Make ("FileError", [ mk loc Types.String (Tast.Local path_slot); mk loc (Types.Int Types.I32) (Tast.Int (Int64.of_int op, Types.I32)); mk loc (Types.Int Types.I32) (Tast.Prim (Tast.Cast (Types.Int Types.I32), [ rt loc (Types.Int Types.I64) "flan_file_fail_reason" [] ])) ])) in let signal () = mk loc Types.Never (Tast.Signal (Tast.Serror, type_id "FileError", cond)) in (* One step of the attempt: run the runtime call, record whether it worked, and signal if it did not. The last step a caller gives is what leaves [ok] true, which is what stops the loop. *) let try_ (attempt : Tast.expr) = mk loc Types.Unit (Tast.Do [ mk loc Types.Unit (Tast.Set (Tast.Plocal ok, mk loc Types.Bool (Tast.Prim (Tast.Ne, [ attempt; i8 0L ])))); mk loc Types.Unit (Tast.If (notok (), signal (), unit_at loc)) ]) in let clause name params = let sg = restart_sig (List.map snd params) in { Tast.rname_id = type_id name; rname = name; rparams = params; rsig = sg; rsig_id = type_id sg; rbody = [ unit_at loc ] } in let body = mk loc Types.Unit (Tast.RestartCase ([ clause "retry" []; clause "use-value" [ (path_slot, Types.String) ] ], mk loc Types.Unit (Tast.Do (mk_steps try_)))) in mk loc Types.Unit (Tast.Let ([ (ok, mk loc Types.Bool (Tast.Bool false)) ], [ mk loc Types.Unit (Tast.While (notok (), [ body ], [])) ])) (* Is this bare symbol the name of a type? Every table [resolve_name] will look in, and the data type table is one of them: a data type is [Named] exactly as a struct is, so (vec-new Form) is as ordinary as (vec-new Cell). It was left out when data types landed, which made the prelude's own (vec-new Form) fail with "nothing here says what (vec-new) is a Vec of" — a message about a missing annotation for a program that had written one. One list, read by both callers, so the next kind of type added cannot be added to one of them. *) and type_named ctx n = (* A type variable names a type here too, which is what lets [(vec-new t)] be written in a generic body: inside an instantiation [resolve_name] answers with the concrete element type, and during the abstract pass it answers [Var t] and the [Vec] that comes back is a [(Vec t)] — generic, and refused by anything that needs a size. *) List.mem n ctx.env.tyvars || List.mem_assoc n ctx.env.subst || List.mem n Types.primitive_names || Hashtbl.mem ctx.env.structs n || Hashtbl.mem ctx.env.datas n || Hashtbl.mem ctx.env.unions n || Hashtbl.mem ctx.env.enums n || Hashtbl.mem ctx.env.aliases n (* The element type for [vec-new]: a leading bare symbol naming a type, or the expectation at the site. A bare symbol shadowed by a local or a global is that binding — an allocator, in practice — and not a type. *) and vec_new_elem ctx ~want loc args = let named = match args with | { Ast.e = Ast.Var n; _ } :: rest when lookup ctx n = None && (not (Hashtbl.mem ctx.env.globals n)) && type_named ctx n -> Some (resolve_name ctx.env ~seen:[] loc n, rest) | _ -> None in match named with | Some (t, rest) -> t, rest | None -> (match want with | Some (Types.Vec t) -> t, args | _ -> fail loc "nothing here says what (vec-new) is a Vec of — write the element \ type, as (vec-new i32), or give the binding a type") (* The key and value types, or the reason this is not a Map. *) and map_kv loc what (t : Types.t) = match t with | Types.Map (k, v) -> k, v | other -> fail loc "%s takes a (Map K V), found %s" what (Types.to_string other) (* The key and value for [map-new]: two leading bare symbols naming types, or the expectation at the site. The same rule [vec-new] uses, with the same escape for a symbol that is really a binding — an allocator, in practice — and the pair is written together or not at all, because (map-new string) says half of a type and half is not a type. *) and map_new_types ctx ~want loc args = let is_type n = lookup ctx n = None && (not (Hashtbl.mem ctx.env.globals n)) && type_named ctx n in match args with | { Ast.e = Ast.Var k; _ } :: { Ast.e = Ast.Var v; _ } :: rest when is_type k && is_type v -> resolve_name ctx.env ~seen:[] loc k, resolve_name ctx.env ~seen:[] loc v, rest | { Ast.e = Ast.Var k; _ } :: rest when is_type k && rest = [] -> fail loc "(map-new %s) names a key and no value — write both, as (map-new %s \ i32), or give the binding a type" k k | _ -> (match want with | Some (Types.Map (k, v)) -> k, v, args | _ -> fail loc "nothing here says what (map-new) maps — write the key and value \ types, as (map-new string i32), or give the binding a type") (* The element type for [pool-new]. The same rule [vec-new] uses and for the same reason: a [let] has no type annotation, so a local pool has nowhere else to say what it holds. *) and pool_new_elem ctx ~want loc args = let named = match args with | { Ast.e = Ast.Var n; _ } :: rest when lookup ctx n = None && (not (Hashtbl.mem ctx.env.globals n)) && type_named ctx n -> Some (resolve_name ctx.env ~seen:[] loc n, rest) | _ -> None in match named with | Some (t, rest) -> if move_only ctx.env.tvpreds t then fail loc "(Pool %s) holds a move-only element, and the type-erased runtime \ copies and releases slots bytewise. Recursive teardown arrives with \ drop (step 5 in NEXT.md)" (Types.to_string t); t, rest | None -> (match want with | Some (Types.Pool t) -> t, args | _ -> fail loc "nothing here says what (pool-new) is a Pool of — write the element \ type, as (pool-new Enemy), or give the binding a type") (* The element type, or the reason this is not a Pool. *) and pool_elem loc what (t : Types.t) = match t with | Types.Pool e -> e | other -> fail loc "%s takes a (Pool T), found %s" what (Types.to_string other) (* The element type, or the reason this is not a Vec. *) and vec_elem loc what (t : Types.t) = match t with | Types.Vec e -> e | other -> fail loc "%s takes a (Vec T), found %s" what (Types.to_string other) (* The allocator an operation uses: the one named at the site, or the current implicit one. spec-memory.md: an operation never falls back to a hidden global allocator, and an explicit allocator can override the context. *) and allocator_arg ctx loc = function | [] -> rt loc Types.Alloc "flan_context_allocator" [] | [ a ] -> check ctx ~want:Types.Alloc a | _ -> fail loc "at most one allocator may be named here" (* The address of an element, bounds-checked, with the allocator's epoch checked first. Both the value form [(at v i)] and the place form [(set (at v i) x)] come through here, so they cannot drift apart — which is the asymmetry [nth] was removed for. *) and vec_at ctx loc (target : Tast.expr) (idx : Ast.expr list) = let elem = vec_elem loc "at" target.Tast.ty in match idx with | [ i ] -> let i = index_expr ctx i in rt loc (Types.Ptr elem) "flan_vec_at" [ target; i; size_of loc elem; here loc ], elem | _ -> fail loc "a Vec takes exactly one index — (at v i) — and its element is indexed \ separately" and named_call ctx ~want loc name args = let prim p ty args = expect loc ~want (mk loc ty (Tast.Prim (p, args))) in match name with (* ── arithmetic and comparison ─────────────────────────────────── *) | "+" | "-" | "*" | "/" -> let p = match name with | "+" -> Tast.Add | "-" -> Tast.Sub | "*" -> Tast.Mul | _ -> Tast.Div in fold_arity loc name args; fold_left_prim ctx ~want loc name p Types.is_numeric "numbers" args (* Remainder stays at two: (% a b c) is (% (% a b) c), which is a thing nobody writes on purpose. *) | "%" -> arity loc name 2 args; let a, b = binary ctx name loc ~want:(numeric_want want) args in unconstrained ctx.env loc name ~needs:"numeric?" a.Tast.ty; if not (Types.is_numeric a.Tast.ty || generic_ty a.Tast.ty) then fail loc "%s takes numbers, found %s" name (Types.to_string a.Tast.ty); prim Tast.Rem a.Tast.ty [ a; b ] | "=" | "!=" | "<" | "<=" | ">" | ">=" -> let p = match name with | "=" -> Tast.Eq | "!=" -> Tast.Ne | "<" -> Tast.Lt | "<=" -> Tast.Le | ">" -> Tast.Gt | _ -> Tast.Ge in arity loc name 2 args; let a, b = binary ctx name loc ~want:None args in (* [=] and [!=] admit one type [<] does not: a handle, which is a pair of numbers in one word and where "the same entity" is the question the type exists to answer. Ordering handles would order a slot index, which is a free-list artefact and means nothing. *) let ok = match name with | "=" | "!=" -> Types.is_equatable a.Tast.ty | _ -> Types.is_comparable a.Tast.ty in unconstrained ctx.env loc name ~needs:(match name with "=" | "!=" -> "equal?" | _ -> "ordered?") a.Tast.ty; if not (ok || generic_ty a.Tast.ty) then fail loc "%s compares machine numbers; %s has no built-in comparison \ (plan.org, Types)" name (Types.to_string a.Tast.ty); prim p Types.Bool [ a; b ] | "not" -> arity loc name 1 args; prim Tast.Not Types.Bool [ check ctx ~want:Types.Bool (List.hd args) ] (* Bitwise operators are integers-only, and the shift count has the same type as the value shifted — there is no implicit widening anywhere else either. *) | "bit-and" | "bit-or" | "bit-xor" -> let p = match name with | "bit-and" -> Tast.BitAnd | "bit-or" -> Tast.BitOr | _ -> Tast.BitXor in fold_arity loc name args; fold_left_prim ctx ~want loc name p (function Types.Int _ -> true | _ -> false) "integers" args (* The shifts stay at two, and not only because a shift chain reads badly: each count would be checked against the same width below, so (<< x 30 30) would pass two legal shifts and still shift the value away entirely. *) | "<<" | ">>" -> let p = if String.equal name "<<" then Tast.Shl else Tast.Shr in arity loc name 2 args; let a, b = binary ctx name loc ~want:(numeric_want want) args in (match a.Tast.ty with | Types.Int _ -> () | other -> fail loc "%s takes integers, found %s" name (Types.to_string other)); (* A shift by the operand's own width or more is poison in LLVM, which at -O2 turns the whole function into an undefined value rather than into a wrong number. A literal count is rejected here — that is the typo — and [emit] masks a computed one, so no shift can reach the hardware out of range. *) (match a.Tast.ty, b.Tast.e with | Types.Int k, Tast.Int (n, _) when p = Tast.Shl || p = Tast.Shr -> let w = Int64.of_int (Types.bits k) in if Int64.unsigned_compare n w >= 0 then fail loc "%s by %Ld is out of range for %s, which is %d bits wide" name n (Types.to_string a.Tast.ty) (Types.bits k) | _ -> ()); prim p a.Tast.ty [ a; b ] (* (min a b) and (max a b) evaluate each operand once — hence the slots — because a min over two calls must not call either of them twice. Which is also why this one does not go through [fold_left_prim]: there is no Prim to fold, and the pair it folds is a whole comparison. Each step puts *both* of its sides in slots, the accumulated pick included, so the three-operand form is two nested lets and still exactly one evaluation of each operand — where reusing the previous [If] as an operand of the next would have duplicated everything inside it. *) | "min" | "max" -> fold_arity loc name args; let x, y, rest = match args with x :: y :: rest -> x, y, rest | _ -> assert false in let a, b = binary ctx name loc ~want:(numeric_want want) [ x; y ] in (* [min] and [max] are [<] with a pick, so [ordered?] is what they want — not [numeric?]. A generic that declares [ordered?] gets both. *) unconstrained ctx.env loc name ~needs:"ordered?" a.Tast.ty; if not (Types.is_numeric a.Tast.ty || generic_ty a.Tast.ty) then fail loc "%s takes numbers, found %s" name (Types.to_string a.Tast.ty); let ty = a.Tast.ty in let cmp = if String.equal name "min" then Tast.Lt else Tast.Gt in let pick a b = let sa = fresh_slot ctx ty and sb = fresh_slot ctx ty in let la = mk loc ty (Tast.Local sa) and lb = mk loc ty (Tast.Local sb) in let test = mk loc Types.Bool (Tast.Prim (cmp, [ la; lb ])) in mk loc ty (Tast.Let ([ (sa, a); (sb, b) ], [ mk loc ty (Tast.If (test, la, lb)) ])) in expect loc ~want (List.fold_left (fun acc arg -> pick acc (check ctx ~want:ty arg)) (pick a b) rest) (* (zeroed) is the all-bytes-zero value of whatever it is being stored into, so it only means anything where a type is expected of it. *) | "zeroed" -> arity loc name 0 args; (match want with | Some ty when ty <> Types.Never -> no_zeroed_fn loc "this" ty; mk loc ty (Tast.Zero ty) | _ -> fail loc "zeroed needs to know the type it is zeroing — use it where one is \ expected, as in (set grid (zeroed))") (* The one half of a destructuring [let] that [Parse] cannot do on its own. Everything else about a pattern is bindings and field accesses it already wrote; the arity is a *type* question — how many elements the value has — and there are no types in the parser. So the pattern's shape travels here as arguments: which element this binding wants, how many names the pattern binds, and whether that count is exact or a minimum (it is a minimum when the pattern ends in [& rest]). No source symbol can contain a [~] — the reader makes it a delimiter — so this name is unspellable and nothing but [Parse] can reach it. *) | "destructure~nth" -> (match args with | [ target; { Ast.e = Ast.Int i; _ }; { Ast.e = Ast.Int n; _ }; { Ast.e = Ast.Int exact; _ } ] -> let plural k = if Int64.equal k 1L then "" else "s" in let target = check ctx target in (match target.Tast.ty with | Types.Array (m, elem) -> if Int64.equal exact 1L && not (Int64.equal m n) then fail loc "this pattern binds %Ld name%s, but %s has %Ld element%s — a \ pattern over a fixed array names every element, or ends in \ [& rest]" n (plural n) (Types.to_string target.Tast.ty) m (plural m); if Int64.equal exact 0L && Int64.compare m n < 0 then fail loc "this pattern binds %Ld name%s before the &, but %s has only %Ld \ element%s" n (plural n) (Types.to_string target.Tast.ty) m (plural m); prim Tast.At elem [ target; mk loc index_ty (Tast.Int (i, Types.I32)) ] (* The asymmetry is real and is the reason this is refused rather than lowered to a bounds-checked [at]: a fixed array's length is in its type, so [[a b]] over a [[2 f32]] is a claim the checker can settle, and over a [[T]] it is a claim about a number that does not exist until the program runs. Turning it into a runtime trap would be a pattern that type checks and then kills the program, which is the trade this language does not make. *) | Types.Slice _ -> fail loc "a pattern cannot destructure %s: a slice's length is a runtime \ value, so nothing here can check that it has %Ld element%s. Use \ (at s i) and test (len s) yourself" (Types.to_string target.Tast.ty) n (plural n) | other -> fail loc "%s is not a fixed array, so [a b ...] cannot destructure it" (Types.to_string other)) | _ -> fail loc "destructure~nth is written by the compiler and cannot be called") (* ── allocators, spec-memory.md ────────────────────────────────── *) (* Every one of these is an ordinary named call, which is the whole of the escape NEXT.md describes: [check_call] already routes a named call through here, so none of the four function-value refusals is anywhere near it. *) (* A *user-written* allocator, and the reason it is still refused now that function values exist. NEXT.md said it needed "a defn's name in value position"; it has that, and it is still two things short, both of them nameable and neither of them a function-value question any more. The built-in set needs none of it: heap-allocator and arena-new are C symbols the emitter names, and no Flan type mentions them. *) | "make-allocator" | "allocator-from" | "allocator" -> fail loc "a user-written allocator is not implemented yet, and a defn's name in \ value position — which is what this used to wait for — is no longer \ what is missing. Two things are. The runtime calls an allocator as \ proc(a, mode, p, old, size, align): six C arguments and no transfer \ channel, and every Flan function value's signature ends with one, so \ the pointer would be called with the wrong shape (the same mismatch a \ foreign function's address is refused for). And Allocator is opaque \ and pointer-width, so there is nowhere for a program to put the \ flan_allocator the pointer would have to point at. Use \ (arena-new ...) with a backing buffer, which is the parameterised \ allocator that does exist" | "heap-allocator" -> arity loc name 0 args; expect loc ~want (mk loc Types.Alloc (Tast.Prim (Tast.Rt "flan_heap_allocator", []))) (* The capacity is explicit and there is no growing backing store: an arena whose size is decided by the program is one a program can reason about, and it is the only shape under which "exhausted" is a state a test can reach on purpose. *) | "arena-new" -> arity loc name 1 args; let cap = check ctx ~want:(Types.Int Types.I64) (List.hd args) in expect loc ~want (mk loc Types.Alloc (Tast.Prim (Tast.Rt "flan_arena_new", [ cap ]))) (* Hands the pages back, which [free-all] deliberately does not — see docs/BUILT.md, "free-all is retain-capacity". *) | "arena-destroy" -> arity loc name 1 args; let a = check ctx ~want:Types.Alloc (List.hd args) in expect loc ~want (mk loc Types.Unit (Tast.Prim (Tast.Rt "flan_arena_destroy", [ a ]))) (* One of spec-memory.md's two release points. It takes the source location as a string so that an allocator with no region to release names the site rather than the runtime. *) | "free-all" -> arity loc name 1 args; let a = check ctx ~want:Types.Alloc (List.hd args) in expect loc ~want (mk loc Types.Unit (Tast.Prim (Tast.Rt "flan_alloc_free_all", [ a; here loc ]))) (* The capability set, read off the allocator value. Odin asks its procedure (Query_Features returning an Allocator_Mode_Set); a field is the same answer without the round trip, which is NEXT.md's call. *) | "can-free?" -> arity loc name 1 args; let a = check ctx ~want:Types.Alloc (List.hd args) in expect loc ~want (mk loc Types.Bool (Tast.Prim (Tast.Ne, [ mk loc (Types.Int Types.I8) (Tast.Prim (Tast.Rt "flan_alloc_can_free", [ a ])); mk loc (Types.Int Types.I8) (Tast.Int (0L, Types.I8)) ]))) | "can-free-all?" -> arity loc name 1 args; let a = check ctx ~want:Types.Alloc (List.hd args) in expect loc ~want (mk loc Types.Bool (Tast.Prim (Tast.Ne, [ mk loc (Types.Int Types.I8) (Tast.Prim (Tast.Rt "flan_alloc_can_free_all", [ a ])); mk loc (Types.Int Types.I8) (Tast.Int (0L, Types.I8)) ]))) (* The counter [free-all] bumps. A container records it and traps if it moved; this is the same number, readable, so a program can say what it saw. *) | "alloc-epoch" -> arity loc name 1 args; let a = check ctx ~want:Types.Alloc (List.hd args) in expect loc ~want (mk loc (Types.Int Types.I64) (Tast.Prim (Tast.Rt "flan_alloc_epoch", [ a ]))) (* The allocator's identity — its address — which is what the condition's :allocator field carries, so a handler holding several regions can tell which one ran out. *) | "alloc-id" -> arity loc name 1 args; let a = check ctx ~want:Types.Alloc (List.hd args) in expect loc ~want (mk loc (Types.Int Types.I64) (Tast.Prim (Tast.Rt "flan_alloc_id", [ a ]))) (* A ceiling on live bytes, 0 for none. spec-memory.md's retry restart is answerable only by a handler that can make the *same* request succeed, and for a fixed backing store the handler that works is the one that grows it: releasing the region a container lives in invalidates the container, which is what the epoch check catches. So the spec's "grows the arena and then invokes retry" needs a ceiling to raise, and this is it. It is also how a program exhausts an allocator on purpose. *) | "alloc-budget" -> arity loc name 1 args; let a = check ctx ~want:Types.Alloc (List.hd args) in expect loc ~want (mk loc (Types.Int Types.I64) (Tast.Prim (Tast.Rt "flan_alloc_budget", [ a ]))) | "set-alloc-budget" -> arity loc name 2 args; (match args with | [ a; n ] -> let a = check ctx ~want:Types.Alloc a in let n = check ctx ~want:(Types.Int Types.I64) n in expect loc ~want (mk loc Types.Unit (Tast.Prim (Tast.Rt "flan_alloc_set_budget", [ a; n ]))) | _ -> assert false) (* "Did you forget to free" is an allocator-tier question and this is the tier answering it — spec-memory.md, "Leaking is defined behaviour". *) | "alloc-live-blocks" -> arity loc name 1 args; let a = check ctx ~want:Types.Alloc (List.hd args) in expect loc ~want (mk loc (Types.Int Types.I64) (Tast.Prim (Tast.Rt "flan_alloc_live_blocks", [ a ]))) (* (with-allocator A BODY...). It rebinds and releases nothing: not at the end of the body, not anywhere. spec-memory.md is explicit that this is not a scope-end release point and that it is the point on which Odin's [defer delete] and Carp's scope-end frees were both rejected. *) | "with-allocator" -> (match args with | [] -> fail loc "with-allocator is (with-allocator allocator body ...)" | a :: body -> let a = check ctx ~want:Types.Alloc a in let body, ty = scoped ctx (fun () -> match body with | [] -> [ unit_at loc ], Types.Unit | _ -> let rec go = function | [ last ] -> let l = check ctx ?want last in [ l ], l.Tast.ty | e :: rest -> let e = check ctx e in let rest, ty = go rest in e :: rest, ty | [] -> assert false in go body) in expect loc ~want (mk loc ty (Tast.WithAlloc (a, body)))) (* ── (Vec T), spec-memory.md ───────────────────────────────────── *) (* Every one of these is a named call over a type-erased runtime, with size_of and align_of produced here because here is where the concrete element type is known. No generics are involved and none are needed. *) (* (vec-new), (vec-new T), (vec-new a), (vec-new T a). [let] has no type annotation — parse.ml settles that a triple binding is ambiguous and types are inferred — so a local Vec has nowhere to say what it holds, and the element type is written at the call instead. This is not the explicit instantiation syntax the generics section rules out: nothing here is generic, and the name is resolved as an ordinary type, not bound to a type variable. Where the context does say — a defvar's type, a function's return type, an argument — it is not needed and may be left out. *) | "vec-new" -> let elem, args = vec_new_elem ctx ~want loc args in let a = allocator_arg ctx loc args in let v = fresh_slot ctx (Types.Vec elem) in let attempt = rt loc (Types.Int Types.I8) "flan_vec_init" [ mk loc (Types.Vec elem) (Tast.Local v); a; i64_at loc 0L; size_of loc elem; align_of loc elem; here loc ] in expect loc ~want (mk loc (Types.Vec elem) (Tast.Let ([ (v, mk loc (Types.Vec elem) (Tast.Zero (Types.Vec elem))) ], [ with_note loc (alloc_guard ctx loc attempt) (reg_note loc "flan_dev_reg_note_vec" (mk loc (Types.Vec elem) (Tast.Local v)) [ size_of loc elem ] elem); region_check ctx.env loc (mk loc (Types.Vec elem) (Tast.Local v)) (mk loc (Types.Vec elem) (Tast.Local v)) ]))) (* Unit, not a Result and not an ignorable error code: see [alloc_guard]. *) | "push" -> arity loc name 2 args; (match args with | [ target; x ] -> let target = borrowed ctx target (fun () -> check ctx target) in let elem = vec_elem loc "push" target.Tast.ty in let x = check ctx ~want:elem x in (* The element is bound before the loop so that a [retry] re-attempts the allocation and not the expression that produced the value. *) let e = fresh_slot ctx elem in let attempt = rt loc (Types.Int Types.I8) "flan_vec_push" [ target; addr_of loc (mk loc elem (Tast.Local e)); size_of loc elem; align_of loc elem; here loc ] in (* Re-noted after every push, not only the first: a push that grows the Vec moves the storage, and the note is keyed on the base address, so an unmoved block costs a probe and an overwrite with the same numbers. This is the insert per allocation NEXT.md settles on, and the settled answer to what it costs is "measure a real program". *) expect loc ~want (mk loc Types.Unit (Tast.Let ([ (e, x) ], [ region_check ctx.env loc target (with_note loc (alloc_guard ctx loc attempt) (reg_note loc "flan_dev_reg_note_vec" target [ size_of loc elem ] elem)) ]))) | _ -> assert false) | "reserve" -> arity loc name 2 args; (match args with | [ target; n ] -> let target = borrowed ctx target (fun () -> check ctx target) in let n = check ctx ~want:index_ty n in let n64 = mk loc (Types.Int Types.I64) (Tast.Prim (Tast.Cast (Types.Int Types.I64), [ n ])) in (* Deferred: the sizes are known abstractly but the hash is not, so the node is a unit no-op and the copy builds the real one. *) if (match target.Tast.ty with | Types.Map (k, _) -> deferred_key ctx.env loc "reserve" k | _ -> false) then expect loc ~want (mk loc Types.Unit Tast.Unit) else let attempt, note = match target.Tast.ty with (* For a map the number is entries, not slots: the runtime sizes the block so that [n] still sits under the 75% load factor, which is the only reading of "room for n" that does not reallocate on the nth put. *) | Types.Map (k, v) -> let hash, _ = key_fns ctx.env loc k in rt loc (Types.Int Types.I8) "flan_map_reserve" [ target; n64; size_of loc k; size_of loc v; hash; here loc ], reg_note loc "flan_dev_reg_note_map" target [ size_of loc k; size_of loc v ] target.Tast.ty | _ -> let elem = vec_elem loc "reserve" target.Tast.ty in rt loc (Types.Int Types.I8) "flan_vec_reserve" [ target; n64; size_of loc elem; align_of loc elem; here loc ], reg_note loc "flan_dev_reg_note_vec" target [ size_of loc elem ] elem in expect loc ~want (region_check ctx.env loc target (with_note loc (alloc_guard ctx loc attempt) note)) | _ -> assert false) (* (as-slice v) and (as-slice v lo hi) — spec-memory.md, "Borrowing". The result is a non-owning view: copying it copies ptr+len and never the elements, and it carries no allocator, so freeing through one is not expressible. A push, a put or a reserve may invalidate it; that is the explicit Zig/Odin contract the spec chose over a borrow checker. *) | "as-slice" -> (match args with | target :: rest when List.length rest = 0 || List.length rest = 2 -> let target = borrowed ctx target (fun () -> check ctx target) in let elem = vec_elem loc "as-slice" target.Tast.ty in let lo, hi = match rest with | [] -> mk loc index_ty (Tast.Int (0L, Types.I32)), (* -1 is "to the end": (as-slice v) has no static length to pass. *) mk loc index_ty (Tast.Int (-1L, Types.I32)) | [ lo; hi ] -> index_expr ctx lo, index_expr ctx hi | _ -> assert false in let out = fresh_slot ctx (Types.Slice elem) in let fill = rt loc Types.Unit "flan_vec_as_slice" [ target; addr_of loc (mk loc (Types.Slice elem) (Tast.Local out)); lo; hi; size_of loc elem; here loc ] in expect loc ~want (mk loc (Types.Slice elem) (Tast.Let ([ (out, mk loc (Types.Slice elem) (Tast.Zero (Types.Slice elem))) ], [ fill; mk loc (Types.Slice elem) (Tast.Local out) ]))) | _ -> fail loc "as-slice is (as-slice v) or (as-slice v lo hi)") (* spec-memory.md's first release point. It consumes its argument exactly as any other move does — the source binding is dead afterwards and using it is a compile error — which is the rule that already makes a double free unrepresentable, so [free] needs no analysis of its own. *) | "free" -> arity loc name 1 args; let target = check ctx (List.hd args) in (* A container of owning elements is refused here, and a reader will assume the opposite — that [free] recurses — so this says why it does not and what does. The bytes this container holds are element *headers*, and releasing the block those headers sit in says nothing about the blocks they point at. Nothing type-erased can walk them: the runtime sees a size and an alignment and has never heard of the element type. That is the same fact the type-level refusals used to state, and the arena did not change it — what the arena changed is that it no longer matters there, because the inner blocks came out of the same region and [free-all] takes them with everything else. So the honest answer is not to recurse, and it is not to release the backing store quietly either. Releasing the outer block alone would be "I freed it" spelt over a program that leaked everything inside, and this file refuses that collapse everywhere else — [flan_alloc_free_all] traps rather than no-op for the same reason. It is refused instead, at the one place a reader is looking when they want to know. The guard at construction is what makes the advice reachable: such a container is region-allocated or it does not exist, so there is always a [free-all] to point at. *) (match target.Tast.ty with | (Types.Vec _ | Types.Map _ | Types.Pool _) when region_only ctx.env target.Tast.ty -> fail loc "%s holds elements that own storage, and free releases the block \ those elements sit in — not the blocks they point at, which nothing \ type-erased can reach. This container was built against a region \ allocator, because the guard at its construction admits no other, so \ release the region: (free-all a) takes it and everything its \ elements own, in one operation and with no per-element teardown" (Types.to_string target.Tast.ty) | Types.Vec elem -> expect loc ~want (rt loc Types.Unit "flan_vec_free" [ target; size_of loc elem; align_of loc elem; here loc ]) | Types.Map (k, v) -> expect loc ~want (rt loc Types.Unit "flan_map_free" [ target; size_of loc k; size_of loc v; here loc ]) (* The owner, not a slot. Every handle into it is stale afterwards and answers None, which is a strictly better afterlife than a Vec's binding gets — that one is a compile error and this one is a run-time answer, because handles are copies and the checker cannot see them all. That asymmetry is the reason handles exist. *) | Types.Pool elem -> expect loc ~want (rt loc Types.Unit "flan_pool_free" [ target; size_of loc elem; align_of loc elem; here loc ]) | Types.Handle _ -> fail loc "free takes the owner, and a handle owns nothing — it is a copyable \ number, so consuming one copy would say nothing about the others. \ (release p h) recycles one slot; (free p) releases the pool" | other -> (* A field is never freed on its own: it would leave its owner partly dead with no way to say so. *) fail loc "free takes a move-only value — a Vec, a Map, or a struct that owns \ one — found %s. A resource type with a drop hook is step 5 and does \ not exist yet" (Types.to_string other)) (* (clone v) uses the current allocator, (clone v a) names one. A deep, independent copy: spec-memory.md's "copying is always explicit". *) | "clone" -> (match args with | target :: rest when List.length rest <= 1 -> (* Checked once, then dispatched on what it turned out to be: checking it inside a guard as well would allocate the target's slots twice and evaluate whatever it was written as twice. *) let target = borrowed ctx target (fun () -> check ctx target) in let a = allocator_arg ctx loc rest in (match target.Tast.ty with (* The refusal that did *not* come down with the type-level ones, and the distinction is worth being exact about, because the sentence they all used to share bundled two different failures: that a clone would duplicate inner headers instead of copying, and that a free would leak what those headers own. Only the second was about teardown, and only the second is answered by a region. What disqualifies [clone] is not that it copies a header — so do [at] and [get], and they are fine, because they promise nothing and hand back an alias into a region nobody individually frees. It is that [clone] *allocates a new block and promises independence*. spec-memory.md calls it a deep copy; what a memcpy of the slots delivers is a second container whose elements still point into the first one's blocks. Two containers, one set of inner buffers, under a name that says otherwise — and putting the copy in a second arena makes it worse, not better, because tipping that arena leaves the copy's elements pointing into an arena that is still live while its own storage is gone. Refused at the operation rather than at the type, because that is where the promise is made. *) | (Types.Vec _ | Types.Map _) when region_only ctx.env target.Tast.ty -> fail loc "%s cannot be cloned: clone is a deep, independent copy, and the \ type-erased runtime copies slots bytewise — so the copy's \ elements would still point at the original's blocks, which is an \ alias under a name that promises the opposite. Nothing here can \ walk an element to copy what it owns. Build a second container \ and insert into it, or keep the one you have — a region makes \ sharing safe, not copying" (Types.to_string target.Tast.ty) (* A map's clone reinserts rather than copying the block, because the seed is derived from the block's address — see flan_rt.c. That is the runtime's business; from here it is one more allocating call under the same guard. *) | Types.Map (k, v) when deferred_key ctx.env loc "clone" k -> (* Deferred, and the placeholder is a zeroed map of the same type — the value a (map-new) starts from, so everything written around the clone still checks against the type it will have. *) let mty = Types.Map (k, v) in expect loc ~want (mk loc mty (Tast.Zero mty)) | Types.Map (k, v) -> let mty = Types.Map (k, v) in let hash, _ = key_fns ctx.env loc k in let d = fresh_slot ctx mty in let attempt = rt loc (Types.Int Types.I8) "flan_map_clone" [ mk loc mty (Tast.Local d); target; a; size_of loc k; size_of loc v; hash; here loc ] in expect loc ~want (mk loc mty (Tast.Let ([ (d, mk loc mty (Tast.Zero mty)) ], [ with_note loc (alloc_guard ctx loc attempt) (reg_note loc "flan_dev_reg_note_map" (mk loc mty (Tast.Local d)) [ size_of loc k; size_of loc v ] mty); mk loc mty (Tast.Local d) ]))) (* Refused by name rather than falling through to "clone takes a (Vec T)". Copying a pool would duplicate every slot *and* every generation counter, so a handle into the original would resolve in the copy too — two live entities behind one identity, which is the exact confusion the type exists to prevent. If a program wants a second world it builds one and inserts into it, and the new handles say they are new. *) | Types.Pool _ -> fail loc "a pool cannot be cloned: the copy would carry the same slot \ generations, so one handle would resolve in both and name two \ different things. Build a second pool and insert into it" | _ -> let elem = vec_elem loc "clone" target.Tast.ty in let d = fresh_slot ctx (Types.Vec elem) in let attempt = rt loc (Types.Int Types.I8) "flan_vec_clone" [ mk loc (Types.Vec elem) (Tast.Local d); target; a; size_of loc elem; align_of loc elem; here loc ] in expect loc ~want (mk loc (Types.Vec elem) (Tast.Let ([ (d, mk loc (Types.Vec elem) (Tast.Zero (Types.Vec elem))) ], [ with_note loc (alloc_guard ctx loc attempt) (reg_note loc "flan_dev_reg_note_vec" (mk loc (Types.Vec elem) (Tast.Local d)) [ size_of loc elem ] elem); mk loc (Types.Vec elem) (Tast.Local d) ])))) | _ -> fail loc "clone is (clone v) or (clone v allocator)") (* ── (Pool T) and (Handle T), spec-memory.md ───────────────────── *) (* The same type-erased shape the Vec has, for the same reason: size_of and align_of are produced here because here is where the concrete element type is known, and nothing below the call site has ever heard of it. *) (* (pool-new), (pool-new T), (pool-new a), (pool-new T a). *) | "pool-new" -> let elem, args = pool_new_elem ctx ~want loc args in let a = allocator_arg ctx loc args in let pty = Types.Pool elem in let p = fresh_slot ctx pty in (* [flan_pool_init] cannot fail — a pool with no slots allocates nothing — but it goes under the guard anyway, so that the day it does allocate the site is already the one that signals. *) let attempt = rt loc (Types.Int Types.I8) "flan_pool_init" [ mk loc pty (Tast.Local p); a; size_of loc elem; align_of loc elem; here loc ] in expect loc ~want (mk loc pty (Tast.Let ([ (p, mk loc pty (Tast.Zero pty)) ], [ with_note loc (alloc_guard ctx loc attempt) (reg_note loc "flan_dev_reg_note_pool" (mk loc pty (Tast.Local p)) [ size_of loc elem ] elem); region_check ctx.env loc (mk loc pty (Tast.Local p)) (mk loc pty (Tast.Local p)) ]))) (* (insert p x) -> (Handle T). The handle is the *only* way back to what was inserted: a pool hands out no index and no pointer, because an index does not notice a reuse and that is the entire point. *) | "insert" -> arity loc name 2 args; (match args with | [ target; x ] -> let target = borrowed ctx target (fun () -> check ctx target) in let elem = pool_elem loc "insert" target.Tast.ty in let x = check ctx ~want:elem x in let hty = Types.Handle elem in (* The element is bound before the loop so that a [retry] re-attempts the allocation and not the expression that produced the value — [push]'s rule, and for the same reason. *) let e = fresh_slot ctx elem in let h = fresh_slot ctx hty in let attempt = rt loc (Types.Int Types.I8) "flan_pool_insert" [ target; addr_of loc (mk loc elem (Tast.Local e)); addr_of loc (mk loc hty (Tast.Local h)); size_of loc elem; align_of loc elem; here loc ] in expect loc ~want (mk loc hty (Tast.Let ([ (e, x); (h, mk loc hty (Tast.Zero hty)) ], [ region_check ctx.env loc target (with_note loc (alloc_guard ctx loc attempt) (reg_note loc "flan_dev_reg_note_pool" target [ size_of loc elem ] elem)); mk loc hty (Tast.Local h) ]))) | _ -> assert false) (* (resolve p h) -> (Option (Ptr T)). A pointer and not a value, and spec-memory.md settles it rather than this lane guessing: its worked example under "Mutating something you matched" is written out as (Option (Ptr Enemy)), for the reason stated a line above it — "pattern bindings bind values, so a matched struct is a copy", and a copy cannot be written back. Mutating the pooled thing in place is what a pool is for, so (Option T) would answer a question nobody asked. An [Option] rather than a trap because the whole thesis is that a stale reference *reports* — the same shape (get m k) has, and for the same reason: absence is an answer, not a failure. The hole, said plainly: the (Ptr T) is invalidated by any [insert] that grows the pool, exactly as a slice is invalidated by a [push]. The handle survives that and the pointer does not. It is spec-memory.md's explicit Zig/Odin contract one level down, and it is worth naming because it is the silent-wrong-answer mode the handle just removed, reintroduced for anyone who keeps the pointer across an insert. Chunked never-moving storage is the fix and it costs code; taking the contract is the smaller correct thing, given [as-slice] already established it. *) | "resolve" -> arity loc name 2 args; (match args with | [ target; h ] -> let target = borrowed ctx target (fun () -> check ctx target) in let elem = pool_elem loc "resolve" target.Tast.ty in let h = check ctx ~want:(Types.Handle elem) h in (match h.Tast.ty with | Types.Handle e when Types.equal e elem -> () | other -> fail loc "resolve takes a (Handle %s), found %s" (Types.to_string elem) (Types.to_string other)); let pty = Types.Ptr elem in let oty = Types.Option pty in let out = fresh_slot ctx pty in let got = rt loc pty "flan_pool_resolve" [ target; h; size_of loc elem; here loc ] in (* The runtime answers a pointer or NULL and the Option is built here, which is [get]'s arrangement: the runtime has no idea what an Option's layout is, and keeping it that way is what lets one entry point serve every element type. *) let cond = mk loc Types.Bool (Tast.Prim (Tast.Ne, [ mk loc (Types.Int Types.I64) (Tast.Prim (Tast.Cast (Types.Int Types.I64), [ mk loc pty (Tast.Local out) ])); mk loc (Types.Int Types.I64) (Tast.Int (0L, Types.I64)) ])) in let some = mk loc oty (Tast.Some_ (mk loc pty (Tast.Local out))) in let none = mk loc oty Tast.None_ in expect loc ~want (mk loc oty (Tast.Let ([ (out, got) ], [ mk loc oty (Tast.If (cond, some, none)) ]))) | _ -> assert false) (* (release p h) -> bool: true if this call released it, false if the handle was already gone. This is how a pooled value dies, and it is not [free]. [free] consumes its argument as a move, and a handle is a copyable number that owns nothing — consuming one copy would say nothing about the others. The pool is the owner, so the release operation is on the pool and takes the handle as an ordinary argument. spec-memory.md's two release points are untouched: (free p) is release point 1 applied to the owner, and a free-all of the region takes the pool with everything else. This is a third thing and it is not a release point — it recycles a slot inside storage the pool still owns. It answers a bool rather than () because the generational scheme makes a double release *detectable*, which is worth handing to the caller: this is the one place in the language where freeing something twice is an answer instead of a refusal. *) | "release" -> arity loc name 2 args; (match args with | [ target; h ] -> let target = borrowed ctx target (fun () -> check ctx target) in let elem = pool_elem loc "release" target.Tast.ty in let h = check ctx ~want:(Types.Handle elem) h in (match h.Tast.ty with | Types.Handle e when Types.equal e elem -> () | other -> fail loc "release takes a (Handle %s), found %s" (Types.to_string elem) (Types.to_string other)); let got = rt loc (Types.Int Types.I8) "flan_pool_release" [ target; h; here loc ] in expect loc ~want (mk loc Types.Bool (Tast.Prim (Tast.Ne, [ got; mk loc (Types.Int Types.I8) (Tast.Int (0L, Types.I8)) ]))) | _ -> assert false) (* (live p) — how many slots are live now. (len p) is the *slot high-water*, which is deliberately the other number: 0..(len p) are the indices (pool-handle p i) accepts, so a loop bounded by [len] visits every live entry. Bounding it by the live count instead would silently skip entries the moment anything had been released, which is precisely the kind of quiet wrong answer this whole type exists to remove. *) | "live" -> arity loc name 1 args; let target = borrowed ctx (List.hd args) (fun () -> check ctx (List.hd args)) in ignore (pool_elem loc "live" target.Tast.ty); let n = rt loc (Types.Int Types.I64) "flan_pool_live" [ target; here loc ] in expect loc ~want (mk loc index_ty (Tast.Prim (Tast.Cast index_ty, [ n ]))) (* (pool-handle p i) -> (Option (Handle T)): the handle of slot [i], or None if that slot is dead. This plus (len p) is the whole of iteration, and iteration is not a convenience — migrate-instances has to *enumerate* live instances, and a pool behind generational handles gives that by construction where a world arena and an owned region do not. It is the reason plan.org's three storage strategies are not a free choice. An index out of 0..(len p) traps, exactly as (at v i) traps: an index is an index here, and answering None for one would hide a bug rather than a death. *) | "pool-handle" -> arity loc name 2 args; (match args with | [ target; i ] -> let target = borrowed ctx target (fun () -> check ctx target) in let elem = pool_elem loc "pool-handle" target.Tast.ty in let i = check ctx ~want:index_ty i in let hty = Types.Handle elem in let oty = Types.Option hty in let out = fresh_slot ctx hty in let got = rt loc hty "flan_pool_handle" [ target; i; here loc ] in (* 0 is the never-valid handle — generation 0 is even, and a live slot's generation is odd — so the runtime says "dead" with it and needs no second return value. *) let cond = mk loc Types.Bool (Tast.Prim (Tast.Ne, [ mk loc (Types.Int Types.I64) (Tast.Prim (Tast.Cast (Types.Int Types.I64), [ mk loc hty (Tast.Local out) ])); mk loc (Types.Int Types.I64) (Tast.Int (0L, Types.I64)) ])) in expect loc ~want (mk loc oty (Tast.Let ([ (out, got) ], [ mk loc oty (Tast.If (cond, mk loc oty (Tast.Some_ (mk loc hty (Tast.Local out))), mk loc oty Tast.None_)) ]))) | _ -> assert false) (* ── (Map K V), spec-memory.md ─────────────────────────────────── *) (* Every one of these is a named call over the same type-erased runtime the Vec uses, with the two sizes and the key's hash and equality pair produced here because here is where the concrete types are known. No generics are involved and none are needed — which is exactly what Odin's Map_Info says too, being two sizes and two contextless procs. *) (* (map-new), (map-new K V), (map-new a), (map-new K V a). The same shape [vec-new] has and for the same reason: a [let] has no type annotation, so a local map has nowhere else to say what it holds. Where the context does say — a defvar's type, a parameter, a return type — the pair may be left out. *) | "map-new" -> let k, v, args = map_new_types ctx ~want loc args in let a = allocator_arg ctx loc args in let mty = map_type ~preds:ctx.env.tvpreds loc k v in let m = fresh_slot ctx mty in let attempt = rt loc (Types.Int Types.I8) "flan_map_init" [ mk loc mty (Tast.Local m); a; size_of loc k; size_of loc v; here loc ] in expect loc ~want (mk loc mty (Tast.Let ([ (m, mk loc mty (Tast.Zero mty)) ], [ with_note loc (alloc_guard ctx loc attempt) (reg_note loc "flan_dev_reg_note_map" (mk loc mty (Tast.Local m)) [ size_of loc k; size_of loc v ] mty); region_check ctx.env loc (mk loc mty (Tast.Local m)) (mk loc mty (Tast.Local m)) ]))) (* (put m k v) — the upsert. Unit, not a Result and not an ignorable error code: see [alloc_guard]. spec-memory.md is explicit that it either inserts or replaces, and that (set (get m k) v) is not map syntax. *) | "put" -> arity loc name 3 args; (match args with | [ target; k; v ] -> let target = borrowed ctx target (fun () -> check ctx target) in let kt, vt = map_kv loc "put" target.Tast.ty in let k = check ctx ~want:kt k in let v = check ctx ~want:vt v in (* Deferred: the arguments are checked — so a move here is still a move and a borrow still a borrow — and the node itself is a unit no-op, thrown away with the rest of the abstract pass. *) if deferred_key ctx.env loc "put" kt then expect loc ~want (mk loc Types.Unit Tast.Unit) else (* Both are bound before the loop, so that a [retry] re-attempts the allocation and not the expressions that produced the key and the value. The same rule [push] follows for its element. *) let ks = fresh_slot ctx kt and vs = fresh_slot ctx vt in let hash, eq = key_fns ctx.env loc kt in let attempt = rt loc (Types.Int Types.I8) "flan_map_put" [ target; addr_of loc (mk loc kt (Tast.Local ks)); addr_of loc (mk loc vt (Tast.Local vs)); size_of loc kt; size_of loc vt; hash; eq; here loc ] in expect loc ~want (mk loc Types.Unit (Tast.Let ([ (ks, k); (vs, v) ], [ region_check ctx.env loc target (with_note loc (alloc_guard ctx loc attempt) (reg_note loc "flan_dev_reg_note_map" target [ size_of loc kt; size_of loc vt ] target.Tast.ty)) ]))) | _ -> assert false) (* (get m k) -> (Option V). Absence is None, not an untyped nil, and the first implementation admits copyable values only, so this is a copy. There is no allocation here and therefore no guard: a lookup that finds nothing is an answer, not a failure. *) | "get" -> arity loc name 2 args; (match args with | [ target; k ] -> let target = borrowed ctx target (fun () -> check ctx target) in let kt, vt = map_kv loc "get" target.Tast.ty in let k = check ctx ~want:kt k in (* Deferred, and the placeholder is [None] rather than [Unit]: this form answers an (Option V), and the abstract pass still has to type-check whatever the body does with the answer. *) if deferred_key ctx.env loc "get" kt then expect loc ~want (mk loc (Types.Option vt) Tast.None_) else let hash, eq = key_fns ctx.env loc kt in let ks = fresh_slot ctx kt in let out = fresh_slot ctx vt in let found = rt loc (Types.Int Types.I8) "flan_map_get" [ target; addr_of loc (mk loc kt (Tast.Local ks)); addr_of loc (mk loc vt (Tast.Local out)); size_of loc kt; size_of loc vt; hash; eq; here loc ] in let oty = Types.Option vt in (* The runtime answers 1/0 and fills [out] only when it answers 1, so the Option is built here rather than there: the runtime has no idea what an Option's layout is, and keeping it that way is what lets one entry point serve every value type. *) let some = mk loc oty (Tast.Some_ (mk loc vt (Tast.Local out))) in let none = mk loc oty Tast.None_ in let cond = mk loc Types.Bool (Tast.Prim (Tast.Ne, [ found; mk loc (Types.Int Types.I8) (Tast.Int (0L, Types.I8)) ])) in expect loc ~want (mk loc oty (Tast.Let ([ (ks, k); (out, mk loc vt (Tast.Zero vt)) ], [ mk loc oty (Tast.If (cond, some, none)) ]))) | _ -> assert false) (* (map-next! m (addr cur) (addr k) (addr v)) -> bool, and the whole of map iteration. Before it there was no way to read a map's keys or its values at all: every other map operation addresses one entry by hashing it, and nothing walked the block. Three out-pointers rather than a returned pair, because there are no tuples and a (Option K) would answer only half of an entry — the value would then cost a second hash of the key just answered. The cursor is an i64 the caller owns and the loop reads as one: (let [cur 0 k 0 v 0] (while (map-next! m (addr cur) (addr k) (addr v)) ...)) It is *not* a generic (map-keys m): a Vec of them needs a signature naming K, and a prelude defn cannot be written at every K. That one is generics, not iteration, and it stays refused for that reason. No hash and no equality pair go with it — walking asks nothing about a key — so this is the one map entry point whose signature carries neither, and the sizes are still needed because the runtime is type-erased. *) | "map-next!" -> arity loc name 4 args; (match args with | [ target; cur; k; v ] -> let target = borrowed ctx target (fun () -> check ctx target) in let kt, vt = map_kv loc "map-next!" target.Tast.ty in let cur = check ctx ~want:(Types.Ptr (Types.Int Types.I64)) cur in let k = check ctx ~want:(Types.Ptr kt) k in let v = check ctx ~want:(Types.Ptr vt) v in let found = rt loc (Types.Int Types.I8) "flan_map_next" [ target; cur; k; v; size_of loc kt; size_of loc vt; here loc ] in expect loc ~want (mk loc Types.Bool (Tast.Prim (Tast.Ne, [ found; mk loc (Types.Int Types.I8) (Tast.Int (0L, Types.I8)) ]))) | _ -> assert false) (* (has-key? m k). (get m k) answers the same question, but through an Option the caller then has to match; this is the form a condition wants, and it copies no value. *) | "has-key?" -> arity loc name 2 args; (match args with | [ target; k ] -> let target = borrowed ctx target (fun () -> check ctx target) in let kt, vt = map_kv loc "has-key?" target.Tast.ty in let k = check ctx ~want:kt k in (* Deferred, and the placeholder is a [bool] — the form a condition wants, so the condition around it still has to check. *) if deferred_key ctx.env loc "has-key?" kt then expect loc ~want (mk loc Types.Bool (Tast.Bool false)) else let hash, eq = key_fns ctx.env loc kt in let ks = fresh_slot ctx kt in let found = rt loc (Types.Int Types.I8) "flan_map_has" [ target; addr_of loc (mk loc kt (Tast.Local ks)); size_of loc kt; size_of loc vt; hash; eq; here loc ] in expect loc ~want (mk loc Types.Bool (Tast.Let ([ (ks, k) ], [ mk loc Types.Bool (Tast.Prim (Tast.Ne, [ found; mk loc (Types.Int Types.I8) (Tast.Int (0L, Types.I8)) ])) ]))) | _ -> assert false) (* ── Assets, decision 1: embedded at compile time ────────────── Odin's #load and #load_directory are the model (src/parser.cpp, src/check_builtin.cpp's check_load_directive), and the reason it is the right answer here is the one NEXT.md gives: it is a *compiler* feature, so it needs no build flags, no linker arguments and no per-target packaging, and it works identically on desktop and web. That matters more here than it does for Odin, because [Load] gives link flags only to a directory package — the single file doing (rl/load-texture "brush.png") is structurally the one file with no link channel. Embedding has no such hole. Odin's `#` is not imported. An s-expression language already has a head position for a name, so these are ordinary named calls spelled [embed] and [embed-dir], resolved here exactly as [vec-new] and [heap-allocator] are. The result costs nothing at run time: the bytes become a `private unnamed_addr constant` string, the same one every string literal already becomes, and emit.ml's [escape] is byte-exact, so a PNG survives the round trip through the .ll. Bound with [defconst], an [embed-dir] becomes an LLVM constant outright (emit.ml's [const]). The one sharp edge, and it is not new: the slice this hands back points into .rodata, so a store through it either segfaults at -O0 or is deleted at -O2 — the same measured trap the prelude's ASCII-case note describes for (bytes "Hi"). Clone the bytes into a Vec for a mutable copy. Nothing here widens that hole; it inherits it, and provenance is what would close it. *) | "embed" -> (match args with | [ p ] | [ p; _ ] -> (* The spelling is settled before the file is opened, so a program that asks for a type embed cannot read a file as is told that, rather than being told the file is missing and left to discover the other half after fixing it. *) (match args with | [ _; { Ast.e = Ast.Var "string"; _ } ] | [ _ ] -> () | [ _; t ] -> fail t.Ast.loc "embed's second argument is the type to read the file as, and \ `string` is the only one — (embed \"p\") is the [u8]" | _ -> ()); let data = read_embed_file (embed_path loc p) p.Ast.loc in let as_string () = mk loc Types.String (Tast.Str data) in (* A [Str] node typed [u8] rather than a [Bytes] prim over one. [Bytes] is identity — emit.ml lowers String and Slice _ to the same %slice — and the prim would make the node non-constant, so an (embed-dir) in a defconst could not be an LLVM constant. Both of emit.ml's string emitters take the bytes and ignore the node's type, so this is the same constant either way, and it is one a global can hold. *) let as_bytes () = mk loc (Types.Slice (Types.Int Types.U8)) (Tast.Str data) in (* Two spellings rather than one that changes type with its context. Odin threads a type_hint everywhere and can afford (embed "p") to mean a string here and a []u8 there; with structural equality and no implicit widening anywhere, the same text meaning two types would be a wart. [want] is a fallback only, and nothing depends on it. *) (match args with | [ _; { Ast.e = Ast.Var "string"; _ } ] -> expect loc ~want (as_string ()) | _ -> (match want with | Some Types.String -> as_string () | _ -> expect loc ~want (as_bytes ()))) | _ -> fail loc "embed is (embed \"path\") for a [u8], or (embed \"path\" string)") | "embed-dir" -> arity loc name 1 args; let arg = List.hd args in let entries = read_embed_dir (embed_path loc arg) arg.Ast.loc in if not (Hashtbl.mem ctx.env.structs "EmbedFile") then fail loc "embed-dir answers a [n EmbedFile] and EmbedFile is not in scope — it \ is a prelude type and something has replaced the prelude"; let ety = Types.Named "EmbedFile" in let elems = List.map (fun (nm, data) -> mk loc ety (Tast.Make ("EmbedFile", [ mk loc Types.String (Tast.Str nm); mk loc (Types.Slice (Types.Int Types.U8)) (Tast.Str data) ]))) entries in expect loc ~want (mk loc (Types.Array (Int64.of_int (List.length entries), ety)) (Tast.Arr elems)) (* ── slurp and barf, decisions 2 and 5 ───────────────────────── [slurp] reads a whole file and answers a (Vec u8). It allocates, which is why it waited for Vec, and it follows spec-memory.md's rule to the letter: no allocating operation returns an error, so there is no Result here and no out-parameter — a failure to allocate is StorageExhausted under [retry] and a failure to read is FileError under [retry] and [use-value]. The two guards nest rather than merge, and that is the point: they are two different failures with two different answerable questions, and a handler that grows an arena is not the handler that supplies another path. Everything is inside the file loop, so a [use-value] that names a different file re-measures it and re-allocates for its size. The Vec is freed at the top of each turn, which is why a retry does not leak; freeing a Vec that never allocated is a no-op (flan_rt.c, flan_vec_free). *) | "slurp" -> (match args with | path :: rest when List.length rest <= 1 -> let path = check ctx ~want:Types.String path in let a = allocator_arg ctx loc rest in let ps = fresh_slot ctx Types.String in let psv () = mk loc Types.String (Tast.Local ps) in let u8 = Types.Int Types.U8 in let vt = Types.Vec u8 in let v = fresh_slot ctx vt in let vv () = mk loc vt (Tast.Local v) in let n = fresh_slot ctx (Types.Int Types.I64) in let nv () = mk loc (Types.Int Types.I64) (Tast.Local n) in let steps try_ = [ (* The size first, because it is the step that does not allocate: a missing file is found before any storage is committed to it. *) try_ (rt loc (Types.Int Types.I8) "flan_file_size" [ psv (); addr_of loc (nv ()) ]); (* Previous turn's storage, if a retry brought us back here. *) rt loc Types.Unit "flan_vec_free" [ vv (); size_of loc u8; align_of loc u8; here loc ]; with_note loc (alloc_guard ctx loc (rt loc (Types.Int Types.I8) "flan_vec_init" [ vv (); a; nv (); size_of loc u8; align_of loc u8; here loc ])) (reg_note loc "flan_dev_reg_note_vec" (vv ()) [ size_of loc u8 ] u8); (* Fills the Vec the line above sized. A file that grew since the measurement is truncated to the buffer; one that shrank leaves a shorter Vec. Both are successful reads of what was there. *) try_ (rt loc (Types.Int Types.I8) "flan_slurp_into" [ vv (); psv () ]) ] in expect loc ~want (mk loc vt (Tast.Let ([ (ps, path); (n, i64_at loc 0L); (v, mk loc vt (Tast.Zero vt)) ], [ file_guard ctx loc ~path_slot:ps ~op:0 steps; vv () ]))) | _ -> fail loc "slurp is (slurp path) or (slurp path allocator)") (* [barf] writes a whole file, and on the web target it signals — every time, with the path in the condition. Decision 2, and the reason is worth having at the call site: Flan has NO conditional compilation, so "isolate this to desktop" is not expressible in source and a build-time refusal would be unusable; a silent no-op is worse than either, because that is how a save file disappears with nothing said. So the program gets a condition and decides. Nothing here reads the target — the refusal is flan_rt.c's, one #ifdef in the host layer, which is exactly where the two targets are already implemented twice. *) | "barf" -> arity loc name 2 args; (match args with | [ path; data ] -> let path = check ctx ~want:Types.String path in let data = byte_slice ctx data in let ps = fresh_slot ctx Types.String in let ds = fresh_slot ctx (Types.Slice (Types.Int Types.U8)) in let steps try_ = [ try_ (rt loc (Types.Int Types.I8) "flan_file_write" [ mk loc Types.String (Tast.Local ps); mk loc (Types.Slice (Types.Int Types.U8)) (Tast.Local ds) ]) ] in (* Both operands are bound before the loop so that a retry re-attempts the write and not the expressions that produced it — the same rule alloc_guard states for push. *) expect loc ~want (mk loc Types.Unit (Tast.Let ([ (ps, path); (ds, data) ], [ file_guard ctx loc ~path_slot:ps ~op:1 steps ]))) | _ -> assert false) (* ── containers ────────────────────────────────────────────────── *) (* [at] and [len] were already the names for a fixed array and a slice, so a Vec extends them rather than adding a parallel pair — which is the asymmetry [nth] was removed for. A Vec's length is i32 like every other length here (index_ty): widening indices is one change across all of them and not a Vec question. *) | "len" -> arity loc name 1 args; let target = List.hd args in let a = borrowed ctx target (fun () -> check ctx target) in (match a.Tast.ty with | Types.Array _ | Types.Slice _ | Types.String -> prim Tast.Len index_ty [ a ] | Types.Vec _ -> let n = rt loc (Types.Int Types.I64) "flan_vec_len" [ a; here loc ] in expect loc ~want (mk loc index_ty (Tast.Prim (Tast.Cast index_ty, [ n ]))) (* Extended rather than given a name of its own, for the reason [at] and [len] were extended over Vec: one question, one word. *) | Types.Map _ -> let n = rt loc (Types.Int Types.I64) "flan_map_len" [ a; here loc ] in expect loc ~want (mk loc index_ty (Tast.Prim (Tast.Cast index_ty, [ n ]))) (* A pool's [len] is its slot high-water, not its live count, so that 0..(len p) stays the range of valid indices the way it is for every other container here. (live p) is the other number. *) | Types.Pool _ -> let n = rt loc (Types.Int Types.I64) "flan_pool_len" [ a; here loc ] in expect loc ~want (mk loc index_ty (Tast.Prim (Tast.Cast index_ty, [ n ]))) | other -> fail loc "len takes an array, a slice, a string, a Vec, a Map or a Pool, \ found %s" (Types.to_string other)) | "at" -> (match args with | target :: idx when idx <> [] -> let target = borrowed ctx target (fun () -> check ctx target) in (match target.Tast.ty with | Types.Vec _ -> let p, elem = vec_at ctx loc target idx in expect loc ~want (mk loc elem (Tast.Deref p)) | _ -> let idx, ty = indexed ctx target idx in prim Tast.At ty (target :: idx)) | _ -> fail loc "%s is (%s collection index ...)" name name) | "slice" -> arity loc name 3 args; (match args with | [ target; lo; hi ] -> let target = check ctx target in let elem = match target.Tast.ty with | Types.Array (_, t) | Types.Slice t -> t | other -> fail loc "slice takes an array or a slice, found %s" (Types.to_string other) in prim Tast.Slice (Types.Slice elem) (let lo_loc = lo.Ast.loc and hi_loc = hi.Ast.loc in let lo = check ctx ~want:index_ty lo in let hi = check ctx ~want:index_ty hi in let ty = target.Tast.ty in (* A bound may sit one past the end, so the length is checked against lo and hi both, not against the last valid index. *) (match literal lo with | Some k -> static_index lo_loc ty ~past_end:true "slice bound" k | None -> ()); (match literal hi with | Some k -> static_index hi_loc ty ~past_end:true "slice bound" k | None -> ()); (match literal lo, literal hi with | Some a, Some b when a > b -> fail loc "slice [%Ld %Ld) runs backwards — lo must not exceed hi" a b | _ -> ()); [ target; lo; hi ]) | _ -> assert false) (* (slice-from-ptr p n) — NEXT.md, "a pointer from C needs a length before it can be indexed". A (Ptr T) that came back from C is readable at element 0 through [deref] and nowhere else, because [indexed] takes an Array or a Slice and a pointer is neither. C hands back an address and no length, so the length has to come from the caller, and this is the form that says so out loud. **What the caller is promising**, and the compiler checks none of it: that [p] really addresses [n] consecutive [T], that they are initialised, and that they outlive every use of the result. Get it wrong and this reads memory that is not there — the bounds check the result carries will agree with a length that was a lie, because the length *is* the lie. It is the same trust [declare-c] already extends, written at the one site where somebody had to know the answer anyway. No marker on the name. A [!] in this language means *mutates* ([map-next!]) and a [?] means *asks* ([font-valid?]), and this does neither; [zeroed], the nearest neighbour — a value conjured rather than derived — carries no marker either. [ptr] is the marker: a (Ptr T) only ever arrives from a [declare-c], so the word already names the C boundary, and a reader who sees it has already been told where the promise comes from. **It owns nothing.** The result is a [Types.Slice], which is not move-only, carries no allocator, and is the same non-owning view (as-slice v) answers — so [free] refuses it by the rule it already had ("free takes a move-only value"), and nothing in the move analysis needed to learn about this form. *) | "slice-from-ptr" -> arity loc name 2 args; (match args with | [ target; n ] -> let target = check ctx target in let elem = match target.Tast.ty with | Types.Ptr t -> t | other -> fail loc "slice-from-ptr takes a (Ptr T) and the number of elements behind \ it, found %s. It is for a pointer that came back from C, whose \ length only the caller knows" (Types.to_string other) in let n_loc = n.Ast.loc in let n = check ctx ~want:index_ty n in (* A negative literal is a lie the checker can see, so it does not wait for the run-time test emit.ml plants beside it. *) (match literal n with | Some k when k < 0L -> fail n_loc "slice-from-ptr length %Ld is negative — the length is what the \ caller promises the pointer addresses, and no pointer addresses \ fewer than zero elements" k | _ -> ()); prim Tast.SliceFromPtr (Types.Slice elem) [ target; n ] | _ -> assert false) (* ── pointers ──────────────────────────────────────────────────── *) | "addr" -> arity loc name 1 args; let a = List.hd args in (match place_of_expr a with | None -> fail a.Ast.loc "addr takes the address of a place — a name, (.field x), (at a i) \ or (deref p)" | Some p -> let p, ty = check_place ctx a.Ast.loc p in expect loc ~want (mk loc (Types.Ptr ty) (Tast.Addr p))) | "deref" -> arity loc name 1 args; let a = check ctx (List.hd args) in (match a.Tast.ty with | Types.Ptr t -> expect loc ~want (mk loc t (Tast.Deref a)) | other -> fail loc "deref takes a (Ptr T), found %s" (Types.to_string other)) (* ── Option ────────────────────────────────────────────────────── *) | "Some" -> arity loc name 1 args; let inner = match want with Some (Types.Option t) -> Some t | _ -> None in let a = check ctx ?want:inner (List.hd args) in expect loc ~want (mk loc (Types.Option a.Tast.ty) (Tast.Some_ a)) (* ── the milestone-2 host primitives (plan.org) ────────────────── *) | "bytes" -> arity loc name 1 args; prim Tast.Bytes (Types.Slice (Types.Int Types.U8)) [ check ctx ~want:Types.String (List.hd args) ] (* (string b): a [u8] seen as a string. The mirror of (bytes s), spelled the same way — a type name in head position, like (bytes s) and unlike the numeric casts, which go through [is_cast] and really do convert. It costs nothing. emit.ml lowers Types.String and Types.Slice _ to the same %slice, 16 bytes at align 8, so a string and a [u8] are already the identical value at run time; both this and [Bytes] emit as the argument itself. What changes is only what the checker will let the value be passed to — which is the whole gap: i64->bytes answers a [u8] and every declare-c text parameter wants a string, and nothing joined them. Two decisions are baked in here. 1. It does NOT check UTF-8, because `string` does not claim UTF-8. The prelude settles this: valid-utf8? is an ordinary function you call when you care, decode-rune/rune-at/rune-count all take [u8] rather than string, and decode-rune answers {.ok false .width 1} on a malformed byte rather than assuming its input is well-formed. The one place the runtime treats a string differently from a byte slice is flan_escape_bytes, for a string nested in a printed structure, and that is a byte-wise escape table with no decoding in it. So there is no code that would be wrong about a string of arbitrary bytes, and a check here would be the only enforcement point in the language — a claim the rest of it does not make. 2. It does not widen the literal-write hole (NEXT.md, "Writing through a string literal"). That hole is the other direction: (bytes "Hi") hands you a writable-looking slice over constant data. This direction only loses the ability to write — a string is read-only everywhere — so the result of (string b) can reach strictly fewer stores than b could. Provenance is still what the other direction needs; nothing here depends on having it. The one sharp edge is not new but is easier to trip over now: the slice that i64->bytes / f64->bytes / u64->bytes answer is a view into one shared static buffer in the runtime, overwritten by the next such call. Calling it a string does not copy it. Use it before formatting the next number; you cannot hold two at once. *) | "string" -> arity loc name 1 args; prim Tast.StrOfBytes Types.String [ byte_slice ctx (List.hd args) ] | "bytes->f64" -> arity loc name 1 args; prim Tast.BytesToF64 (Types.Float Types.F64) [ byte_slice ctx (List.hd args) ] | "bytes->i64" -> arity loc name 1 args; prim Tast.BytesToI64 (Types.Int Types.I64) [ byte_slice ctx (List.hd args) ] | "f64->bytes" -> arity loc name 1 args; prim Tast.F64ToBytes (Types.Slice (Types.Int Types.U8)) [ check ctx ~want:(Types.Float Types.F64) (List.hd args) ] | "i64->bytes" -> arity loc name 1 args; prim Tast.I64ToBytes (Types.Slice (Types.Int Types.U8)) [ check ctx ~want:(Types.Int Types.I64) (List.hd args) ] | "write-stdout" -> arity loc name 1 args; prim Tast.WriteStdout Types.Unit [ byte_slice ctx (List.hd args) ] (* (println x) and (print x): the structural printer, selected on the type the argument checked to. plan.org, Milestone 5 — "compiler-provided, per concrete type". That is not overloading and needs no type variables: there is no dispatch at run time and no user-supplied printer to pick between. The walk itself is render.ml, shared with the REPL, which is what stops the two from drifting apart. [min]/[max]/[zeroed] above dispatch on the resolved argument type the same way. The slots the slice arm needs come out of the frame of whatever function this call is written in, via [fresh_slot] — allocated once per call site, at check time, not once per iteration of a loop around it. A string prints raw here and quoted inside a structure. Those are not in conflict: (println "hello") has to print hello or it is useless, and (println b) where b has a string field has to quote it or the field cannot be told from the punctuation. The split is exactly top level vs nested, which is why it lives here and not in the walk. *) | "print" | "println" -> arity loc name 1 args; (* Printing is a read, not a move: the walk goes over the value and keeps nothing. Without this, (println v) would consume a Vec and every printing of one would be its last. *) let target = List.hd args in let a = borrowed ctx target (fun () -> check ctx target) in (* ── The allow-list, and what it takes to get on it ─────────────── plan.org names [println] as the one compiler-provided exception — it "selects a structural printer at each concrete instantiation" — and that cannot be reconciled with an abstract pass as written: a pass that decides an operator's legality *without* substituting cannot make an exception for the one operator whose legality is only decidable after substituting. So the exception is made explicit: these two forms are *deferred* to instantiation, and every other operator is answered where it is written. Every member of this list is a place where a refusal moves from the definition to a call site, which is the thing the abstract pass exists to prevent. **That cost is not the same for every member, and the list is not closed.** What makes it bearable is whether the call site has a *stated requirement* to be refused against. [print] and [println] have none and need none: every type prints, so there is no [where] predicate for printability — one would always hold and would be noise on a signature — and there is correspondingly no call site these can be refused at. They are deferred and then always succeed. That is the cheapest possible membership. The map operations — [put], [get], [has-key?], [reserve], [clone], through [deferred_key] beside [key_fns] — are the other kind, and they are here on a different argument. They *can* fail at a concrete type, so deferring them does move a refusal. But [{:where (hashable? $t)}] is in the signature, and it is the author's own written requirement: an instantiation at a non-hashable type is refused against that clause, by name, at the call that asked for the type. That is a refusal the caller can act on and one the generic's author chose to be responsible for — categorically different from an unconstrained [(+ a b)] failing deep in a body with no signature to blame, which is the case the abstract pass exists to prevent and which stays refused at the definition. A generic that does *not* declare the predicate gets no deferral: [deferred_key] checks first, and [map_type] has usually refused the signature already. So the rule for adding to this list is not a headcount. It is: either the operation cannot fail after substituting, or a declared predicate gives its failure a place to land. Anything else is answered here. The node produced here is a unit no-op, thrown away with the rest of the abstract pass. The real printer is selected when the copy is checked with [t] concrete. *) if generic_ty a.Tast.ty then mk loc Types.Unit Tast.Unit else let bslice = Types.Slice (Types.Int Types.U8) in let write x = mk loc Types.Unit (Tast.Prim (Tast.WriteStdout, [ x ])) in let conv pr x = mk loc bslice (Tast.Prim (pr, [ x ])) in let emitter : Render.emitter = { Render.ebytes = write; estr = (fun x -> write (conv Tast.EscapeBytes x)); ei64 = (fun x -> write (conv Tast.I64ToBytes x)); eu64 = (fun x -> write (conv Tast.U64ToBytes x)); ef64 = (fun x -> write (conv Tast.F64ToBytes x)) } in let rc = { Render.structs = Hashtbl.fold (fun _ v acc -> v :: acc) ctx.env.structs []; datas = Hashtbl.fold (fun _ v acc -> v :: acc) ctx.env.datas []; unions = Hashtbl.fold (fun _ v acc -> v :: acc) ctx.env.unions []; enums = Hashtbl.fold (fun k v acc -> (k, v) :: acc) ctx.env.enums []; emit = emitter; (* [println] never follows a pointer, and the allocation registry does not change that. spec-memory.md fixes what it prints — "Ptr and Handle print their address or identity rather than recursively dereferencing" — and a printed line belongs to the program, so it must read the same in a release build, where there is no registry to ask. Following one is the *inspector's* move, and session.ml is where that context is built. *) ptrs = None; alloc = (fun ty -> fresh_slot ctx ty) } in let parts = match a.Tast.ty with | Types.String | Types.Slice (Types.Int Types.U8) -> [ write (mk loc bslice (Tast.Prim (Tast.Bytes, [ a ]))) ] | _ -> Render.render rc 0 a in let nl = if String.equal name "println" then [ write (mk loc bslice (Tast.Prim (Tast.Bytes, [ mk loc Types.String (Tast.Str "\n") ]))) ] else [] in expect loc ~want (mk loc Types.Unit (Tast.Do (parts @ nl))) | "exit" -> arity loc name 1 args; prim Tast.Exit Types.Never [ check ctx ~want:index_ty (List.hd args) ] | "argv" -> arity loc name 0 args; prim Tast.Argv (Types.Slice Types.String) [] (* ── casts: (i32 x), (f64 x), and an enum both ways ──────────────── (i32 e) and (GamepadAxis n) are written here rather than in an arm of their own because they are the same operation: an enum is an i32 at run time — Types.Enum says so — and emit.ml's [cast] already reduces one to its i32 before choosing an instruction. So both directions cost nothing: src and target are equal after that reduction and [cast] answers the value unchanged. Why this does not give the typo back. The property worth keeping is that :spcae at a call site is an error at that site, and it still is: a keyword resolves against the parameter's enum and a bare integer does not fit one. What changes is only that a program can *say* it means the conversion, by name, at the site. The rule was never "an integer is dangerous", it was "an integer must not arrive silently", and a written (GamepadAxis i) is not silent. Three sub-decisions: 1. enum → any numeric is always allowed and never checked. It is lossless to i32 by construction, and a narrower target truncates by the same rule every int→int cast already follows — no special case, and (f32 e) means (f32 (i32 e)) rather than an arbitrary refusal. 2. integer → enum accepts a value that is not a declared member. raylib's gesture is a bitfield and an OR of flags is a legal Gesture that is no single member, so refusing it would refuse correct programs; and session.ml's printer already falls through to the number for an out-of-range enum, on purpose, so refusing to *construct* one while blessing its display would be incoherent. An Option would make every site unwrap for no safety bought, and a literal-only refusal would catch nothing — the bitfield case is a run-time value. 3. Only an integer converts *to* an enum. Not a float, which has no meaning here, and not another enum: an enum-to-enum hop goes through (i32 x) so that both ends are written down. *) | _ when Hashtbl.mem ctx.env.enums name -> arity loc name 1 args; let target = resolve_name ctx.env ~seen:[] loc name in let a = check ctx (List.hd args) in (match a.Tast.ty with | Types.Int _ -> () | other -> fail loc "%s converts an integer to an enum, found %s — an enum or a \ float goes through (i32 x) first" name (Types.to_string other)); prim (Tast.Cast target) target [ a ] (* A cast to a *type variable*: [(t x)] inside a generic body. The name is not one [is_cast] knows, because [is_cast] asks whether the name is a machine type and [t] is not — so this is its own arm, above the ordinary one and below the enums, and it reaches the same [Cast] prim. Inside an instantiation [resolve_name] has already answered with the concrete target, so the copy casts to a real type and the emitter sees nothing unusual. During the abstract pass the target is [Var t] and the [where] clause is what says the cast means anything at all: a cast produces a number, so [numeric?] is what admits it. *) | _ when (List.mem name ctx.env.tyvars || List.mem_assoc name ctx.env.subst) && List.length args = 1 -> let target = resolve_name ctx.env ~seen:[] loc name in unconstrained ctx.env loc ("a cast to " ^ name) ~needs:"numeric?" target; let a = check ctx (List.hd args) in (match a.Tast.ty with | Types.Enum _ -> () | t when Types.is_numeric t || generic_ty t -> () | t -> fail loc "%s converts a number, found %s" name (Types.to_string t)); prim (Tast.Cast target) target [ a ] | _ when is_cast name && List.length args = 1 -> let target = resolve_name ctx.env ~seen:[] loc name in let a = check ctx (List.hd args) in (match a.Tast.ty with | Types.Enum _ -> () | t when Types.is_numeric t -> () | t -> fail loc "%s converts a number, found %s" name (Types.to_string t)); prim (Tast.Cast target) target [ a ] (* ── ordinary calls ────────────────────────────────────────────── *) (* A local or a parameter holding a function value, called by the name it is bound to — which is what the body of [map] looks like. It is checked before the global function table and after every builtin: a binding shadows a defn of the same name (one namespace, ordinary lexical scoping), and nothing shadows [+]. A local of any *other* type falls through to the table, so a program that shadows a function name with an i32 and then calls the function still means the function. *) | _ when (match lookup ctx name with | Some b -> (match b.bty with Types.Fn _ -> true | _ -> false) | None -> false) -> (* The binding the guard already found, read directly. Going back through [check] would repeat the lookup and walk the move and capture paths for a type that is neither move-only nor capturable. *) (match lookup ctx name with | Some b -> call_value ctx ~want loc (mk loc b.bty (Tast.Local b.slot)) args | None -> assert false) | _ when Hashtbl.mem ctx.env.gsigs name -> let vars, params, ret = Hashtbl.find ctx.env.gsigs name in generic_call ctx ~want loc name vars params ret args | _ -> match Hashtbl.find_opt ctx.env.fns name with | Some (params, ret) -> if List.length args <> List.length params then fail loc "%s takes %d argument%s, given %d" name (List.length params) (if List.length params = 1 then "" else "s") (List.length args); let args = map2_lr (fun p a -> check ctx ~want:p a) params args in expect loc ~want (mk loc ret (Tast.Call (name, args))) | None -> if Hashtbl.mem ctx.env.datas name then fail loc "%s is a data type — a data type value names the case too, as (%s.%s {.field value ...})" name name (first_case_name ctx.env name) else if Hashtbl.mem ctx.env.cases name then (* [(U.C)] and [(C)]: a case written as a call. Both are how someone reaches for a constructor, and neither is one. *) let dname, c = Hashtbl.find ctx.env.cases name in fail loc "%s is a case of the data type %s — write (%s.%s {.field value ...}), \ or %s.%s on its own when it has no fields" name dname dname c.Tast.vname dname c.Tast.vname else if Hashtbl.mem ctx.env.structs name then fail loc "%s is a type — a struct value is written (%s {.field value ...})" name name else if String.contains name '/' then unimplemented loc (Printf.sprintf "the call %s into an imported package" name) 4 else Loc.failk "check/unknown-function" loc "unknown function %s" name (* ── A call to a generic function ─────────────────────────────────────── The whole of instantiation, and it is at the call site because the call site is the only place the concrete types exist. Odin does the same thing in the same place: [check_expr.cpp]'s [find_or_generate_polymorphic_procedure] runs from call checking, builds the concrete proc type from the operands, scans the base entity's [gen_procs] for an [are_types_identical] match, and generates a new [Entity] only on a miss. *) and generic_call ctx ~want loc name vars pats pret args = if List.length args <> List.length pats then fail loc "%s takes %d argument%s, given %d" name (List.length pats) (if List.length pats = 1 then "" else "s") (List.length args); (* Arguments first, and with no expectation where the parameter's type still mentions a variable — there is nothing to expect until the argument has said what it is. So an untyped literal falls to its own default and [(id 3)] instantiates at i32, which is the one place inference at a generic call site is weaker than at a monomorphic one. A variable already bound by an earlier argument is substituted back into the parameters still to come, so [(sort-by! (slice ns 0 4) (fn [a b] (< a b)))] works: by the time the [fn] is reached, [(Fn [$t $t] bool)] has become [(Fn [i32 i32] bool)] and the literal has the position it needs to take its types from. Left to right, which is the order Odin's operands are gathered in and the order [map2_lr] already guarantees. *) let subst = ref [] in let targs = map2_lr (fun p a -> let p = subst_ty !subst p in let a = if generic_ty p then check ctx a else check ctx ~want:p a in if not (bind_ty subst p a.Tast.ty) then fail a.Tast.loc "%s expects %s here, found %s" name (Types.to_string p) (Types.to_string a.Tast.ty); a) pats args in (* Every variable has to be determined by an argument. A return-only variable has nothing to bind it — there is no explicit instantiation syntax by design (plan.org) — so it is refused here, where the signature can be named, rather than producing a copy with a hole in it. *) List.iter (fun v -> if not (List.mem_assoc v !subst) then fail loc "%s's type variable $%s is not determined by any argument — a \ generic function is instantiated from its call site, and there is \ no syntax for naming the type" name v) vars; let cparams = List.map (subst_ty !subst) pats in let cret = subst_ty !subst pret in if List.exists generic_ty cparams || generic_ty cret then begin (* One generic function calling another at its *own* variable, seen from the abstract pass over the caller's body — [sort-by!] calling [swap!] at [t]. There is no copy to make yet: [t] is not a type. The node is built so the call still type-checks and is thrown away with the rest of the abstract pass; the real copy is generated when the caller is instantiated and the same call site resolves [t] to a concrete type. But the callee's [where] clause is answerable here, and has to be. The whole promise of the abstract pass is that a generic's refusals arrive at its definition; if the predicate were left to the instantiation, [(defn f [x $t] () (sort! [x]))] would be accepted at its definition and refused at whichever call site first instantiated it — a refusal in code the caller did not write, which is the thing the pass exists to avoid. So the caller has to declare at least what the callee asks for, and [pred_entails] means [ordered?] covers a callee wanting [copyable?] without anyone writing both. *) (match Hashtbl.find_opt ctx.env.generics name with | None -> () | Some gfn -> List.iter (fun (p : Ast.pred) -> match List.assoc_opt p.Ast.pvar !subst with | Some (Types.Var v) when not (declares ctx.env.tvpreds v p.Ast.pname) -> Loc.failk "check/predicate-not-carried" loc "%s is written {:where (%s $%s)}, and this call passes the \ type variable %s, which nothing here declares %s. Add \ {:where (%s $%s)} to this function's own clause — a \ predicate a body relies on has to be carried by every \ signature between it and the call site" name p.Ast.pname p.Ast.pvar v p.Ast.pname p.Ast.pname v | Some t when not (generic_ty t) && not (pred_holds p.Ast.pname t) -> Loc.failk "check/predicate-unsatisfied" loc "%s is written {:where (%s $%s)}, and this call passes %s, \ which is not %s" name p.Ast.pname p.Ast.pvar (Types.to_string t) p.Ast.pname | _ -> ()) gfn.Ast.fwhere); expect loc ~want (mk loc cret (Tast.Call (name, targs))) end else let sym = instantiate ctx.env loc name vars !subst cparams cret in expect loc ~want (mk loc cret (Tast.Call (sym, targs))) (* Cache or generate, Odin's loop. The key is the whole concrete signature compared pairwise with [Types.equal] — [are_types_identical] — so calling at the same type twice makes one copy. *) and instantiate env loc gname vars subst cparams cret = let cache = match Hashtbl.find_opt env.insts gname with | Some r -> r | None -> let r = ref [] in Hashtbl.replace env.insts gname r; r in let same (ps, r, _) = List.length ps = List.length cparams && List.for_all2 Types.equal ps cparams && Types.equal r cret in match List.find_opt same !cache with | Some (_, _, sym) -> sym | None -> let sym = gname ^ "-" ^ String.concat "-" (List.map (fun v -> mangle_ty (List.assoc v subst)) vars) in if Hashtbl.mem env.fns sym then fail loc "%s at these types is called %s, and %s is already defined — rename \ one of them" gname sym sym; runaway env loc gname cparams; (* Each instantiation checks the concrete types answer the [where] clause. This is the half of the feature that only exists per copy: the abstract pass took the predicates on trust, and here is where the trust is settled, at the call site that asked, naming it. *) let fn = Hashtbl.find env.generics gname in List.iter (fun (p : Ast.pred) -> match List.assoc_opt p.Ast.pvar subst with | None -> () | Some t -> if not (pred_holds p.Ast.pname t) then Loc.failk "check/predicate-unsatisfied" loc "this call instantiates %s at $%s = %s, and %s does not \ answer %s — which %s requires, being written {:where (%s \ $%s)}. The requirement is the signature's, so the refusal is \ here, at the call that asked for the type: pass one the \ predicate admits" gname p.Ast.pvar (Types.to_string t) (Types.to_string t) p.Ast.pname gname p.Ast.pname p.Ast.pvar) fn.Ast.fwhere; (* The entry goes in *before* the body is checked, which is what makes a recursive generic function terminate: the call to itself at the same types finds this and does not generate a second copy. *) cache := (cparams, cret, sym) :: !cache; Hashtbl.replace env.fns sym (cparams, cret); let saved_subst = env.subst and saved_vars = env.tyvars and saved_preds = env.tvpreds and saved_chain = env.chain in (* Inside the copy there are no variables left: [resolve_name] answers [t] with the concrete type, so every node the body produces is as concrete as one written out by hand. The [where] clause goes out of scope with them — there is nothing abstract left for it to permit, and every operator is answered by the concrete type it now has. *) env.subst <- List.map (fun v -> (v, List.assoc v subst)) vars; env.tyvars <- []; env.tvpreds <- []; env.chain <- env.chain @ [ (gname, cparams, loc) ]; let restore () = env.subst <- saved_subst; env.tyvars <- saved_vars; env.tvpreds <- saved_preds; env.chain <- saved_chain in let tfn = match !check_fn_ref env { fn with Ast.name = sym } with | tfn -> restore (); tfn | exception e -> restore (); (* A copy whose body did not check is not a copy. Both entries go back out, so a second call at the same types is the same refusal again rather than a cache hit on a function that does not exist. *) cache := List.filter (fun (_, _, s) -> s <> sym) !cache; Hashtbl.remove env.fns sym; raise e in env.instances <- tfn :: env.instances; sym and is_cast name = Types.ikind_of_name name <> None || Types.fkind_of_name name <> None and byte_slice ctx (a : Ast.expr) = check ctx ~want:(Types.Slice (Types.Int Types.U8)) a and numeric_want want = match want with Some (Types.Int _ | Types.Float _) -> want | _ -> None (* Both operands of a binary operator have one type, and there is no implicit widening, so one side has to decide it. Check the side that carries the most information first: a non-literal over a literal, and a float literal over an integer one, since an integer constant converts to a float and not back. *) and binary ctx name loc ~want args = match args with | [ x; y ] -> let y_decides = (is_literal x && not (is_literal y)) || (match x.Ast.e, y.Ast.e with | (Ast.Int _ | Ast.Byte _), Ast.Float _ -> true | _ -> false) in if y_decides then begin let b = check ctx ?want y in let a = check ctx ~want:b.Tast.ty x in a, b end else begin let a = check ctx ?want x in let b = check ctx ~want:a.Tast.ty y in a, b end | _ -> fail loc "%s takes two arguments" name (* ── Declarations: pass 1, collect ─────────────────────────────────── *) (* Constant folding, only over integers and only for defconst — enough for an array length like (/ screen-height cell-size). *) let rec const_int env (e : Ast.expr) : int64 option = match e.Ast.e with | Ast.Int n -> Some n | Ast.Byte b -> Some (Int64.of_int b) | Ast.Var n -> Hashtbl.find_opt env.consts n (* Left to right over any number of operands, because that is how the checker reads the same form: an array length that type-checks as a product of three literals and is then not a constant would be a distinction with nothing behind it. [%] is still two, as it is there. *) | Ast.Call ({ Ast.e = Ast.Var op; _ }, x :: y :: rest) -> let step a b = match op with | "+" -> Some (Int64.add a b) | "-" -> Some (Int64.sub a b) | "*" -> Some (Int64.mul a b) | "/" when b <> 0L -> Some (Int64.div a b) | "%" when b <> 0L && rest = [] -> Some (Int64.rem a b) | _ -> None in List.fold_left (fun acc e -> match acc, const_int env e with | Some a, Some b -> step a b | _ -> None) (const_int env x) (y :: rest) | _ -> None let collect env (decls : Ast.decl list) = (* One pass over every declaration kind before any of the others, because the tables below are per-kind — structs, data types, aliases, enums, functions and globals each have their own — and a collision between two of them would otherwise be found by LLVM, as [redefinition of function '@flan.item'], or not at all. A [defn item] and a [defvar item] are two declarations of one name and are rejected here. *) let claimed = Hashtbl.create 64 in List.iter (fun (d : Ast.decl) -> match Ast.declared_name d with | None -> () | Some n -> (match Hashtbl.find_opt claimed n with | Some first -> (* The second one is the error, because it is the one to delete; the first is the note, because without it the message is a claim the reader has to go and verify. *) Loc.failk "check/defined-twice" d.Ast.dloc ~notes:[ Loc.note first (n ^ " is already defined here") ] "%s is defined twice" n | None -> ()); Hashtbl.add claimed n d.Ast.dloc) decls; (* Names first, so a struct may mention one declared below it. *) List.iter (fun (d : Ast.decl) -> match d.Ast.d with | Ast.Defstruct (n, _) -> Hashtbl.replace env.locs n d.Ast.dloc; Hashtbl.replace env.structs n { Tast.sname = n; fields = [] } | Ast.Defdata (n, _) -> Hashtbl.replace env.locs n d.Ast.dloc; Hashtbl.replace env.datas n { Tast.dname = n; cases = [] } | Ast.Defunion (n, _) -> Hashtbl.replace env.locs n d.Ast.dloc; Hashtbl.replace env.unions n { Tast.sname = n; fields = [] } | Ast.Defalias (n, t) -> Hashtbl.replace env.aliases n t | _ -> ()) decls; (* Compile-time integer constants next, to a fixpoint, because an array length may name a constant declared below it — top-level names in a package are order-independent (plan.org, Modules). *) let fold_consts () = let progress = ref false in List.iter (fun (d : Ast.decl) -> match d.Ast.d with | Ast.Defconst (n, _, v) when not (Hashtbl.mem env.consts n) -> (match const_int env v with | Some i -> Hashtbl.replace env.consts n i; progress := true | None -> ()) | _ -> ()) decls; !progress in while fold_consts () do () done; let field (f : Ast.field) : Tast.field = let fty = resolve env f.Ast.fty in no_zeroed_fn f.Ast.fty.Ast.tloc (Printf.sprintf "the field %s" f.Ast.fname) fty; { Tast.fname = f.Ast.fname; fty } in (* Constants with no declared type are inferred from their value, which needs every other signature in hand — so they are deferred to a pass of their own below. *) let untyped = ref [] in (* Enums come first, in a pass of their own: a signature below may name one, and [resolve] has to find it before it resolves that signature. *) List.iter (fun (d : Ast.decl) -> match d.Ast.d with | Ast.Defenum (n, members) -> let names = List.map fst members in if List.length (List.sort_uniq compare names) <> List.length names then fail d.Ast.dloc "%s declares the same member twice" n; Hashtbl.replace env.enums n members; Hashtbl.replace env.locs n d.Ast.dloc | _ -> ()) decls; List.iter (fun (d : Ast.decl) -> let loc = d.Ast.dloc in match d.Ast.d with | Ast.Package _ -> () | Ast.Defenum _ -> () (* Imports are gone by now: [Load] resolved them into these very decls, so one reaching the checker is a driver that skipped that step. *) | Ast.Import (alias, _) -> fail loc "internal: the import of %s was not resolved before checking" alias (* [Shim.expand] rewrote every one of these into a [Declare] and a [Defn] before [collect] ran, so one arriving here is a driver that skipped that step. *) | Ast.DeclareC (fn, _) -> fail loc "internal: the declare-c of %s was not expanded before checking" fn.Ast.name | Ast.Declare (fn, csym) -> if Hashtbl.mem env.fns fn.Ast.name then fail loc "%s is declared twice" fn.Ast.name; let params = List.map (fun (p : Ast.field) -> resolve env p.Ast.fty) fn.Ast.params in let ret = match fn.Ast.ret with None -> Types.Unit | Some t -> resolve env t in (* What may cross the boundary. A slice or a string goes as ptr+len, a scalar as itself; an aggregate does not go at all, because how one is passed differs per target and reproducing that here would be three calling conventions to maintain. Pass (Ptr T) instead and let the C shim dereference it — that is what the shim is for. *) let crossable what (t : Types.t) = match t with | Types.Int _ | Types.Float _ | Types.Bool | Types.Ptr _ | Types.Enum _ | Types.Unit -> () | Types.String | Types.Slice _ when what = "a parameter" -> () | _ -> fail loc "%s of %s is %s, which cannot cross to C directly — pass \ (Ptr %s) and let the shim read it" what fn.Ast.name (Types.to_string t) (Types.to_string t) in List.iter (crossable "a parameter") params; crossable "the return type" ret; Hashtbl.replace env.fns fn.Ast.name (params, ret); Hashtbl.replace env.externs fn.Ast.name csym | Ast.Defalias _ -> () | Ast.Defstruct (n, fs) -> let names = List.map (fun (f : Ast.field) -> f.Ast.fname) fs in if List.length (List.sort_uniq compare names) <> List.length names then fail loc "%s declares the same field twice" n; let fields = List.map field fs in (* Recorded before the refusal below rather than after it, because the refusal asks [region_only], which walks this very declaration: a recursive value's field is a [(Vec Value)] and answering for it means reading [Value]'s own cases back out of the table. A [fail] aborts the whole compilation, so an entry left behind by a declaration that is about to be refused is never read. *) Hashtbl.replace env.structs n { Tast.sname = n; fields }; (* spec-memory.md: "Ownership is structural, not declared" — a struct containing a Vec is itself move-only, and freeing one recurses into its owning fields while (free (.items b)) is refused because it would leave the owner partly dead. None of that transitive machinery exists, and it is what [drop] would have brought. So the field is still refused at the declaration, where the message can say so, rather than accepted into a struct that copies its header on assignment and gives two owners one buffer. With one exception, and it is exact: a field whose container holds *owning* elements. That container cannot exist outside a region — the guard at its construction is what makes sure of it (see [vec-new]) — so the struct's field is region-allocated too, transitively and by the same guard, and the whole graph is released by one [free-all]. There is nothing for a teardown to recurse into because there is no teardown, and the two-owners-one-buffer problem is not one when the owner is the region and neither copy is it. The plain case stays refused precisely because nothing enforces anything there: a [(Vec i32)] field is happily built against the heap, nothing would object, and then (free (.items b)) through two copies of the struct is a double free with no guard between it and the program. *) List.iter (fun (f : Tast.field) -> if Types.is_move_only f.Tast.fty && not (region_only env f.Tast.fty) then fail loc "%s's field %s is %s, which is move-only, and a struct that \ owns one is move-only too — transitively, with recursive \ teardown and with a field that cannot be freed on its own. \ That rule does not exist; hold the %s in a local and pass \ it. A container whose *elements* own storage is the one \ kind admitted here, because it can only have been built \ against a region allocator and a single (free-all) takes \ the whole graph" n f.Tast.fname (Types.to_string f.Tast.fty) (Types.to_string f.Tast.fty)) fields | Ast.Defdata (n, vs) -> (* A data type with no cases has no value, so nothing could ever be given one, and a parameter of that type would be a function nothing can call. It parses; it is refused here rather than surviving to a layout with a tag and no case for the tag to name. *) if vs = [] then fail loc "%s declares no cases, so no value of it can exist — a data type is \ (defdata %s [(Case [field Type ...]) ...])" n n; let cnames = List.map (fun (v : Ast.variant) -> v.Ast.vname) vs in if List.length (List.sort_uniq compare cnames) <> List.length cnames then fail loc "%s declares the same case twice" n; let cases_with_loc = List.map (fun (v : Ast.variant) -> let fnames = List.map (fun (f : Ast.field) -> f.Ast.fname) v.Ast.vfields in if List.length (List.sort_uniq compare fnames) <> List.length fnames then fail v.Ast.vloc "%s.%s declares the same field twice" n v.Ast.vname; let vfields = List.map field v.Ast.vfields in v.Ast.vloc, { Tast.vname = v.Ast.vname; vfields }) vs in let cases = List.map snd cases_with_loc in (* Registered before the field refusal below, not after, for the reason the struct's copy of this gives: [region_only] has to read this data type's own cases back out to answer for a [(Vec Value)] that names [Value]. The two declarations do this identically because a data type that could hold a container where a struct could not would be a hole in the same rule. *) Hashtbl.replace env.datas n { Tast.dname = n; cases }; (* The same refusal a struct field gets, for the same reason, in the same words, and with the same one exception: a data type case's fields are a struct, the data type copies bytewise on assignment, and there is no recursive teardown to make that safe — except where the field's container holds owning elements, which can only have been built against a region and is therefore released whole. This is the arm the recursive dynamic value needs, and it is worth naming what it buys: a [Value] with a [(Vec Value)] case and a [(Map string Value)] case is now declarable, parsed into an arena, walked, and released by one [free-all] with no per-element teardown anywhere. What it costs is that a [Value] is copied bytewise like any other data value, so two copies share the inner blocks. In a region that is aliasing and not a double free, because neither copy owns anything — the region does. *) List.iter (fun (vloc, (c : Tast.variant)) -> List.iter (fun (f : Tast.field) -> if Types.is_move_only f.Tast.fty && not (region_only env f.Tast.fty) then fail vloc "%s.%s's field %s is %s, which is move-only, and a \ data type case that owns one makes the data type \ move-only too — transitively, with recursive teardown. \ That rule does not exist; hold the %s in a local and \ pass it. A \ container whose *elements* own storage is the one kind \ admitted here, because it can only have been built \ against a region allocator and a single (free-all) \ takes the whole graph" n c.Tast.vname f.Tast.fname (Types.to_string f.Tast.fty) (Types.to_string f.Tast.fty)) c.Tast.vfields) cases_with_loc; List.iter (fun (c : Tast.variant) -> Hashtbl.replace env.cases (n ^ "." ^ c.Tast.vname) (n, c); Hashtbl.replace env.cases c.Tast.vname (n, c)) cases (* ── The untagged union ────────────────────────────────────────── C's semantics, deliberately and in full: the members overlay one storage, the size is the largest of them, the alignment the strictest, and nothing anywhere records which member was written last. {2 What Flan says about reading a member that was not written} It reads the bytes that are there, through that member's type. Not undefined behaviour, and not a refusal either — a *definition*, and this is the one place in the checker that chooses bytes over safety on purpose, so it is worth saying why. Refusing it was the alternative, and it would have made the feature nothing: type punning *is* reading the member that was not written, and both uses this type exists for are that read. Binding a C header means holding the union the library holds and reading whichever member the library's own tag says is live — a tag Flan cannot see, because it is a field of the enclosing struct and the rule that relates them is prose in a manual. Overlaying an f32 on a u32 to look at its bits is the other use and is the same read. A checker that refused it would be refusing the type. So the promise is the one C's implementations actually make and C's standard does not: the layout is the target's, the bytes are the bytes, and a read is a reinterpretation of them. What is *not* promised is anything about bytes never written — a member larger than the one last stored reads its own size, and the tail is indeterminate exactly as a struct's padding is. That is the honest line, and it is narrower than it sounds: the ZII rule means a union starts all-bytes-zero unless [uninit] says otherwise, so the tail is zero rather than garbage in every program that did not ask for garbage. {2 uninit} Allowed, unlike on a data type. The refusal there is not about garbage — [uninit] is garbage everywhere and says so — it is that a data type's tag *steers*, and a tag no case names falls past every comparison in a [match] into a block LLVM is entitled to treat as unreachable. An untagged union steers nothing. Reading a member of one is already a reinterpretation of whatever bytes are there, so [uninit] makes those bytes arbitrary and changes nothing else, which is exactly what it means on an [i64]. {2 Why bool is not a member} An [i1] loaded out of a byte that is neither 0 nor 1 is not a [false], it is a value the optimiser is entitled to assume cannot exist, and a union is the one type that can hand it one — write the [u8] member 2, read the [bool] member. Nothing about that is visible at the read, so it cannot be refused there. The alternative was to load a union's bool as an [i8] and compare it against zero in both backends, which is a correct answer and a real cost paid by every bool in the language to make one type safe. Refused at the declaration instead, where the message can name the replacement: [u8], compared explicitly. The check below is recursive, because a bool inside a struct member is the same byte. {2 Why no member may be move-only} Because nothing knows which member is live, so nothing can tear one down. That is not a limitation of today's compiler, which is what the struct and data type refusals above say about themselves; it is a property of the type, and it does not go away when recursive teardown lands. A [drop] of a union would have to free whichever member is live and there is no such fact — freeing the wrong one is a free of a pointer that was an f64 a moment ago. *) | Ast.Defunion (n, ms) -> if ms = [] then fail loc "%s declares no members, so it has no size and nothing could be \ read out of it — a union is (defunion %s [member Type ...])" n n; let names = List.map (fun (f : Ast.field) -> f.Ast.fname) ms in if List.length (List.sort_uniq compare names) <> List.length names then fail loc "%s declares the same member twice" n; let fields = List.map field ms in List.iter (fun (f : Tast.field) -> if Types.is_move_only f.Tast.fty then fail loc "%s's member %s is %s, which is move-only, and a union may \ not own one: the members overlay one storage and nothing \ records which was written, so nothing can free the right \ one. Unlike a struct's, this is not waiting on recursive \ teardown — there is no fact for teardown to read. Hold the \ %s beside the union, or in a struct with a tag you check \ yourself" n f.Tast.fname (Types.to_string f.Tast.fty) (Types.to_string f.Tast.fty)) fields; Hashtbl.replace env.unions n { Tast.sname = n; fields } | Ast.Defn fn -> (* A signature that introduces a type variable is a *pattern*, not a signature: it goes in [gsigs] and the function goes nowhere near [fns], because nothing can be called at [t]. Every call site turns it into an ordinary entry. *) let vars = signature_tyvars fn in (* The [where] clause is checked against the signature here, once, rather than at every use of it: a predicate nobody has heard of, or one about a variable the signature never bound, is a mistake about this definition and is refused at this definition. *) List.iter (fun (p : Ast.pred) -> if not (List.mem p.Ast.pname predicate_names) then Loc.failk "check/unknown-predicate" p.Ast.ploc "%s is not a type predicate. The ones there are: %s" p.Ast.pname (String.concat ", " predicate_names); if not (List.mem p.Ast.pvar vars) then Loc.failk "check/unbound-predicate-variable" p.Ast.ploc "$%s is not a type variable of %s — a where clause \ constrains the variables the signature binds%s" p.Ast.pvar fn.Ast.name (if vars = [] then ", and this signature binds none" else ", which here are " ^ String.concat ", " (List.map (fun v -> "$" ^ v) vars))) fn.Ast.fwhere; env.tyvars <- vars; env.tvpreds <- fn.Ast.fwhere; let params = List.map (fun (p : Ast.field) -> resolve env p.Ast.fty) fn.Ast.params in let ret = match fn.Ast.ret with None -> Types.Unit | Some t -> resolve env t in env.tyvars <- []; env.tvpreds <- []; if vars = [] then Hashtbl.replace env.fns fn.Ast.name (params, ret) else begin Hashtbl.replace env.generics fn.Ast.name fn; Hashtbl.replace env.gsigs fn.Ast.name (vars, params, ret) end | Ast.Defvar (n, t, _) -> let ty = match t with | Some t -> resolve env t | None -> fail loc "defvar %s needs a type" n in Hashtbl.replace env.globals n (ty, false) | Ast.Defconst (n, Some t, _) -> Hashtbl.replace env.globals n (resolve env t, true) | Ast.Defconst (n, None, v) -> untyped := (n, v) :: !untyped) decls; (* Also to a fixpoint, and for the same reason: one untyped constant may be defined in terms of another declared after it. A constant that still does not check once no progress is left has a real error, so the last round is run without swallowing it. *) let infer (_, v) = (check { env; ret = Types.Unit; slots = 0; slot_tys = []; slot_names = []; scope = []; defers = []; outer = []; outer_what = None; in_frames = None; loops = []; tail = false; in_defer = false; defer_ok = false; defer_block = "a nested form"; dead = []; borrow = false; owner = "" } v).Tast.ty in let pending = ref (List.rev !untyped) in let rec settle () = let left = List.filter (fun ((n, _) as c) -> match infer c with | ty -> Hashtbl.replace env.globals n (ty, true); false | exception Loc.Error _ -> true) !pending in let progressed = List.length left < List.length !pending in pending := left; if progressed && left <> [] then settle () in settle (); List.iter (fun c -> ignore (infer c)) !pending (* A type that contains itself by value has no finite size. [(Ptr T)] and a slice are indirections and break the cycle; a fixed array does not, because it is inline. Caught here rather than when a backend tries to lay the type out or a zero value is built for it — which would not fail, it would hang. *) let check_finite env = let rec walk seen name = if List.mem name seen then fail (Option.value (Hashtbl.find_opt env.locs name) ~default:Loc.unknown) "%s contains itself by value, so it has no size — go through (Ptr %s)" name name; let seen = name :: seen in match Hashtbl.find_opt env.structs name with | Some s -> List.iter (fun (f : Tast.field) -> ty seen f.Tast.fty) s.Tast.fields | None -> match Hashtbl.find_opt env.datas name with | Some u -> List.iter (fun (c : Tast.variant) -> List.iter (fun (f : Tast.field) -> ty seen f.Tast.fty) c.Tast.vfields) u.Tast.cases | None -> (* A union whose member is itself is the same infinite type a struct's is — the size is the largest member and the largest member is the whole thing. Nothing about overlaying storage makes the recursion finite, so it is on the same walk rather than left to hang the layout calculator. *) match Hashtbl.find_opt env.unions name with | None -> () | Some u -> List.iter (fun (f : Tast.field) -> ty seen f.Tast.fty) u.Tast.fields and ty seen = function | Types.Named n -> walk seen n | Types.Array (_, e) | Types.Option e -> ty seen e | _ -> () in Hashtbl.iter (fun n _ -> walk [] n) env.structs; Hashtbl.iter (fun n _ -> walk [] n) env.datas; Hashtbl.iter (fun n _ -> walk [] n) env.unions (* No [bool] and no data type anywhere inside a union, at any depth — see the [Defunion] arm in [collect] for why an [i1] read out of a union is the one punning hazard Flan refuses rather than defines. It runs here, after [collect], because it has to look through a member's *struct* to reach the fields inside it and the struct table is only complete once every declaration has been walked. A union that contains itself is impossible by [check_finite] above, so the recursion terminates without a seen set — except through a [Ptr], which this does not follow: a bool behind a pointer is a bool in someone else's storage and is loaded from an address, not reinterpreted out of a blob. *) let check_union_members env = let rec walk uname where (t : Types.t) = match t with | Types.Bool -> fail (Option.value (Hashtbl.find_opt env.locs uname) ~default:Loc.unknown) "%s is a bool, and a union may not hold one at any depth: writing a \ member that overlays it leaves a byte that is neither 0 nor 1, and \ an i1 with that byte in it is a value the optimiser is entitled to \ assume cannot exist. Hold a u8 in the union and compare it yourself" where (* An [Option] is deliberately not on this list, and the difference is worth stating because a reader will ask. Its [match] lowers to a test of the tag byte and a branch, so a scribbled tag reads as a [Some] with a garbage payload — a number nobody stored, which is exactly what this language says a union read is. A data type's lowers to a chain of comparisons with an [unreachable] after the last one. *) | Types.Array (_, e) | Types.Option e -> walk uname where e | Types.Named n when Hashtbl.mem env.datas n -> fail (Option.value (Hashtbl.find_opt env.locs uname) ~default:Loc.unknown) "%s is %s, a data type, and a union may not hold one at any depth: a \ data type's tag steers every match over it, and overlaying another \ member leaves that tag arbitrary — a tag no case names falls past \ every comparison into a block the optimiser may treat as \ unreachable. This is the same refusal uninit on a data type gets, \ and it arrives here because a union is the other way to hand one \ bytes nobody wrote. Hold the %s beside the union" where n n | Types.Named n -> (match Hashtbl.find_opt env.structs n with | Some st -> List.iter (fun (f : Tast.field) -> walk uname (where ^ "." ^ f.Tast.fname) f.Tast.fty) st.Tast.fields | None -> match Hashtbl.find_opt env.unions n with | None -> () | Some u -> List.iter (fun (f : Tast.field) -> walk uname (where ^ "." ^ f.Tast.fname) f.Tast.fty) u.Tast.fields) | _ -> () in Hashtbl.iter (fun n (u : Tast.structure) -> List.iter (fun (f : Tast.field) -> walk n (n ^ "'s member " ^ f.Tast.fname) f.Tast.fty) u.Tast.fields) env.unions (* ── Declarations: pass 2, check bodies ────────────────────────────── *) let rec check_fn env (fn : Ast.fn) : Tast.fn = let params, ret = Hashtbl.find env.fns fn.Ast.name in let ctx = { env; ret; slots = 0; slot_tys = []; slot_names = []; scope = []; defers = []; outer = []; outer_what = None; in_frames = None; loops = []; tail = false; in_defer = false; defer_ok = false; defer_block = "a nested form"; dead = []; borrow = false; owner = fn.Ast.name } in List.iter2 (fun (p : Ast.field) ty -> if List.mem_assoc p.Ast.fname ctx.scope then begin let first = List.find_opt (fun (q : Ast.field) -> q.Ast.fname = p.Ast.fname) fn.Ast.params in let notes = match first with | Some q when q != p -> [ Loc.note q.Ast.floc ("the first " ^ p.Ast.fname ^ " is here") ] | _ -> [] in Loc.failk "check/duplicate-parameter" p.Ast.floc ~notes "%s has two parameters named %s" fn.Ast.name p.Ast.fname end; ignore (bind ctx p.Ast.fname ty ~assignable:false)) fn.Ast.params params; let body = match fn.Ast.fbody with | [] -> if Types.equal ret Types.Unit then [] else fail fn.Ast.nloc "%s returns %s but has no body" fn.Ast.name (Types.to_string ret) | body -> (* The last form is the return value, unless the function returns Unit, in which case whatever it evaluates to is discarded. *) let want = if Types.equal ret Types.Unit then None else Some ret in (* Every form here is at the top level of the function body, so every one of them may carry a [defer] — and so may a form inside a [let] written here, which is what [ctx.defer_ok] carries down. [check] registers it and yields [unit]; the permission is granted again before each form because [check] withdraws it as it starts. A trailing [defer] is still a [defer] and not the return value, so the expectation is not put to it: it would only ever report [Unit] against the declared return type, which names the wrong problem. *) let is_defer (e : Ast.expr) = match e.Ast.e with Ast.Defer _ -> true | _ -> false in let rec go = function | [ last ] -> ctx.defer_ok <- true; [ (if is_defer last then check ctx last else check ctx ?want last) ] | x :: rest -> ctx.defer_ok <- true; let x = check ctx x in x :: go rest | [] -> assert false in go body in (* Function exit runs the defers, innermost first. An explicit [return] ran its own (see [check]); this is the fall-off-the-end path. A trap does not run them — it is [noreturn] and then [unreachable] — and that is the same rule the bounds checks already follow. *) let body = match ctx.defers with | [] -> body | ds when Types.equal ret Types.Unit -> body @ ds | ds -> (* The result is computed before the defers run and returned after, so it goes through a slot rather than staying the last form. *) let rec split = function | [ last ] -> ([], last) | x :: rest -> let (init, last) = split rest in (x :: init, last) | [] -> assert false in let init, last = split body in let s = fresh_slot ctx ret in let loc = last.Tast.loc in init @ [ mk loc ret (Tast.Let ([ (s, last) ], ds @ [ mk loc ret (Tast.Local s) ])) ] in { Tast.name = fn.Ast.name; params; slots = Array.of_list (List.rev ctx.slot_tys); snames = Array.of_list (List.rev ctx.slot_names); (* The same defers again, for the transfer exit path §5 describes. The normal path has them spliced into [body] above. *) ret; body; fdefers = ctx.defers; fparent = None; floc = fn.Ast.nloc } (* The generic body, checked once with its variables abstract. Nothing is kept — the [Tast.fn] it produces is thrown away, and so is anything it lifted — because a generic function has no code: only its instantiations do. What is kept is the *refusal*: an operator an unconstrained variable does not support fails here, at the definition, naming the variable, rather than at whichever call site happened to instantiate it at a type that worked. The holes in it are real and are the report's business: [println] is plan.org's one compiler-provided exception and this pass rejects it, and move-only-ness is not decidable abstractly at all — [Types.is_move_only (Var _)] is false, but the same variable at [(Vec i32)] is move-only. *) and check_generic env (fn : Ast.fn) = let vars, params, ret = Hashtbl.find env.gsigs fn.Ast.name in let saved_lifted = env.lifted and saved_vars = env.tyvars and saved_preds = env.tvpreds in env.tyvars <- vars; (* What the abstract pass may assume. Every operator the body reaches asks [env.tvpreds] whether the variable was declared to support it, and every instantiation asks the concrete type the same question again. *) env.tvpreds <- fn.Ast.fwhere; Hashtbl.replace env.fns fn.Ast.name (params, ret); let finish () = Hashtbl.remove env.fns fn.Ast.name; env.lifted <- saved_lifted; env.tyvars <- saved_vars; env.tvpreds <- saved_preds in (match check_fn env fn with | _ -> finish () | exception e -> finish (); raise e) (* The knot from [instantiate]: a call site makes a copy, and making one is checking a function. *) let () = check_fn_ref := check_fn (* A global of move-only type is legal, and what makes it legal is [var]'s refusal rather than anything here: reading one is always a borrow, so no function can take it, and none can free it. See [global_borrow] for why that one sentence is enough where a general ownership model would not be. What this pass still decides is how such a global may be *started*, and the answer is zeroed and nothing else. A zeroed Vec is a real empty Vec — null block, zero length, zero capacity — so the ZII value is the value a program would have written anyway, and filling it is an ordinary (set g (slurp "...")) in whichever function loads it. The alternative, a computed initialiser, does not exist to be relaxed into: [Emit.const] says so in as many words ("there is no init-at-startup path, by design"), and the backend that does run initialisers at startup, [x86.ml], runs them from .init_array before main and deliberately omits them from a reload module, because re-running one would wipe the live state reloading exists to preserve. A rule that held on one backend and not the other would not be a rule. That fits what a runtime-loaded global is for. The data is loaded by whoever loads it, once, and it outlives main: a main that returns and is entered again finds the global exactly as it left it, because nothing between the two runs touches it. Assigning a second time overwrites the first block and leaks it — there is no [drop] and no cross-function flow analysis that could see the second assignment, so that is the manual-memory answer and the language's own: free is a thing you write. A global *Allocator* is not any of this — an allocator is a copyable opaque handle — which is what makes the handler-owns-the-arena shape in exhausted.flan expressible. *) let move_only_global_init loc n (ty : Types.t) (init : Ast.init) = if Types.is_move_only ty then match init with | Ast.Zeroed -> () | _ -> fail loc "the global %s is %s, which is move-only, and a move-only global \ starts zeroed: a global's initialiser is a compile-time constant and \ %s is not one. Write (defvar %s %s) with no initialiser — a zeroed \ %s is an empty one, and that is a value, not a placeholder — then \ load it with (set %s ...) in the function that loads it, which runs \ once and whose result outlives every call to main" n (Types.to_string ty) (match init with Ast.Uninit -> "uninit" | _ -> "this initialiser") n (Types.to_string ty) (Types.to_string ty) n (* A move-only global has to be a [defvar]. A [defconst] is not an assignable place — [check_place] refuses one by name — so a constant Vec could only ever hold the zeroed value it was declared with, and nothing could ever put the file's bytes in it. Refused here, where the fix is one keyword, rather than at the (set ...) that discovers it three forms later. *) let no_move_only_defconst loc n (ty : Types.t) = if Types.is_move_only ty then fail loc "the global %s is %s, which is move-only, and a move-only global is a \ defvar and not a defconst: a constant is not an assignable place, so \ nothing could ever load this one — it would stay the empty %s it was \ declared as. Write (defvar %s %s) and fill it in a function" n (Types.to_string ty) (Types.to_string ty) n (Types.to_string ty) (* A union member written into a global would have to be encoded into the blob at link time, which is the byte-level encoder a data type case does not have either — and a global's initialiser is a constant, while a union value is a store. Refused here, where the message can name the way through, rather than at the emitter as "this one is computed", which is true and says nothing. A zeroed union needs none of this and is the ordinary declaration. Both kinds of global, because a defconst reaches the same emitter by a different path. *) let no_union_init env loc n what (v : Tast.expr) = match v.Tast.ty, v.Tast.e with (* The all-bytes-zero value is a constant and needs none of this, so it is the one initialiser that goes through — which is what makes (U {}) and a declaration with no value the same thing here as everywhere else. *) | _, (Tast.Zero _ | Tast.Uninit _) -> () | Types.Named un, _ when Hashtbl.mem env.unions un -> fail loc "the global %s is the union %s, and a union member cannot be written \ into a %s: the initialiser is a constant and storing a member is a \ store. Leave it zeroed and write the member in a function" n un what | _ -> () let check_global env (d : Ast.decl) : Tast.global option = let ctx () = { env; ret = Types.Unit; slots = 0; slot_tys = []; slot_names = []; scope = []; defers = []; outer = []; outer_what = None; in_frames = None; loops = []; tail = false; in_defer = false; defer_ok = false; defer_block = "a nested form"; dead = []; borrow = false; owner = "" } in match d.Ast.d with | Ast.Defvar (n, _, init) -> let ty, _ = Hashtbl.find env.globals n in no_zeroed_fn d.Ast.dloc (Printf.sprintf "the global %s" n) ty; move_only_global_init d.Ast.dloc n ty init; let ginit = match init with | Ast.Zeroed -> { Tast.e = Tast.Zero ty; ty; loc = d.Ast.dloc } | Ast.Uninit -> (* Everywhere else [uninit] is an opt-out from ZII and the bytes are whatever they were: a garbage f64 is a garbage number. A data type is the one type where that is qualitatively worse — the tag steers control flow, a tag no case names falls past every comparison in a [match], and the block after them is [unreachable], which LLVM is entitled to assume cannot happen. So the one place where garbage becomes "the optimiser may do anything" is refused by name, and the zeroed form, which is the first declared case, is named beside it. *) (match ty with | Types.Named un when Hashtbl.mem env.datas un -> fail d.Ast.dloc "%s is a data type, and uninit on one is refused: its tag steers \ every match, and a tag no case names has no arm to reach. Drop \ the uninit — a zeroed %s is %s, which is a real case" (Types.to_string ty) un (match Hashtbl.find_opt env.datas un with | Some { Tast.cases = c :: _; _ } -> un ^ "." ^ c.Tast.vname | _ -> "its first case") | _ -> ()); { Tast.e = Tast.Uninit ty; ty; loc = d.Ast.dloc } | Ast.Init v -> let v = check (ctx ()) ~want:ty v in no_union_init env d.Ast.dloc n "global" v; v in Some { Tast.gname = n; gty = ty; ginit; gconst = false; gfolded = false } | Ast.Defconst (n, _, v) -> let ty, _ = Hashtbl.find env.globals n in no_zeroed_fn d.Ast.dloc (Printf.sprintf "the global %s" n) ty; no_move_only_defconst d.Ast.dloc n ty; (* [collect] already folded the integer constants, because an array length has to be known before any type resolves. Use that value here rather than the expression it came from: a global's initialiser has to be a compile-time constant, and [(/ screen-height cell-size)] is one — the folding pass is the only thing that knows it. *) let ginit = match Hashtbl.find_opt env.consts n, ty with | Some k, Types.Int kind -> (* Still range-checked: this path skips [check], and [in_range] is the only thing that rejects 300 as a u8. *) { Tast.e = Tast.Int (in_range d.Ast.dloc kind k, kind); ty; loc = d.Ast.dloc } | _ -> check (ctx ()) ~want:ty v in no_union_init env d.Ast.dloc n "constant" ginit; (* [env.consts] holds exactly the constants the folding pass consumed, so membership is the question "is this value in the program's shape?" *) Some { Tast.gname = n; gty = ty; ginit; gconst = true; gfolded = Hashtbl.mem env.consts n } | _ -> None (* The entry point, plan.org: (defn main [args [string]] i32), with both the parameter and the return type optional. *) (* Where [main] was written. [env.locs] is the table of where each *type* was declared — [collect] fills it for structs, data types, unions and enums and for nothing else — so a function's own location is not in it and the [find_opt] idiom the rest of this file uses does not apply here. The declaration list does have it, and the caller is holding the list anyway. Without this both refusals below opened with :0:0, which tells a reader that a rule exists and not where they broke it, and gives [next-error] nothing to jump to. A [main] that arrived some other way — a [declare], say — still has no [defn] to point at, so that case keeps the unknown span rather than inventing one. *) let main_loc (decls : Ast.decl list) = let is_main (d : Ast.decl) = match d.Ast.d with Ast.Defn fn -> fn.Ast.name = "main" | _ -> false in match List.find_opt is_main decls with | Some { Ast.d = Ast.Defn fn; _ } -> fn.Ast.nloc | _ -> Loc.unknown let check_main env decls = let at = main_loc decls in match Hashtbl.find_opt env.fns "main" with | None -> () (* a library, or a file being checked on its own *) | Some (params, ret) -> let ok_params = match params with | [] -> true | [ Types.Slice Types.String ] -> true | _ -> false in if not ok_params then fail at "main takes no parameters or one [string], not (%s)" (String.concat " " (List.map Types.to_string params)); if not (Types.equal ret Types.Unit || Types.equal ret (Types.Int Types.I32)) then fail at "main returns i32 or nothing, not %s" (Types.to_string ret) (* The environment as well as the program. A session needs it to check an expression typed at a REPL against the program the process is running — and it has to be this one rather than anything rebuilt from declarations, because [program] prepends the prelude and no accumulated AST contains it. *) (* Separate entry points below rather than a flag on the one the session calls, for the reason [Parse] gives at the same fork: [Loc.Errors] is a second exception that the session and the daemon do not catch, so the guarantee that they never see one should be structural and not a default argument. *) let build_program ~keep_going (decls : Ast.decl list) : Tast.program * env = let env = new_env () in let decls = Parse.program (Prelude.forms ()) @ decls in (* Before anything is collected: every (declare-c ...) becomes an ordinary flattened [declare] with a Flan [defn] over it, and the C that does the flattening comes back to be compiled into the build. Nothing below this line knows the form exists. *) let decls, cshim = Shim.expand decls in (* Pass one, and it stops at the first thing it refuses. That is not laziness: every name, type and signature in the file comes from here, so a declaration this pass could not make sense of leaves a hole that pass two would report once per mention. A wrong signature is one error; the thirty "unknown name" lines under it are not errors, they are the same one. Pass two is where the volume is, and it is where collecting pays. By the time it runs every signature is sound, so a body that fails to check cannot make the next body fail — which is what makes a declaration a resync point that needs no resynchronising. *) collect env decls; check_finite env; check_union_members env; let s = Loc.sink ~on:keep_going in ignore (Loc.caught s (fun () -> check_main env decls)); (* Every generic body, checked once with its variables left abstract, and the result thrown away. This is the pass plan.org's rule needs and Odin has no equivalent of: Odin checks a polymorphic body only per instantiation, so [a + b] over a [$T] compiles there and fails only if nobody ever calls it at a numeric type. plan.org says the opposite — an unconstrained variable supports only what every type supports, and [=], [<], [+] and [hash] over one are *rejected, not silently instantiated*. Rejecting them means type-checking the body with nothing substituted, which is this, and it is a second pass over the same source. *) List.iter (fun (d : Ast.decl) -> match d.Ast.d with | Ast.Defn fn when Hashtbl.mem env.gsigs fn.Ast.name -> ignore (Loc.caught s (fun () -> check_generic env fn)) | _ -> ()) decls; let globals = List.filter_map (fun d -> Option.join (Loc.caught s (fun () -> check_global env d))) decls in let fns = List.filter_map (fun (d : Ast.decl) -> match d.Ast.d with (* A generic [defn] does not reach the typed IR at all. Only its instantiations do, and they are collected below. *) | Ast.Defn fn when Hashtbl.mem env.gsigs fn.Ast.name -> None | Ast.Defn fn -> Loc.caught s (fun () -> check_fn env fn) | _ -> None) decls in Loc.finish s; (* The handler clauses lifted out along the way. They are ordinary functions from here down; nothing in the backend knows they were written inside something else. *) let fns = fns @ List.rev env.lifted in (* The copies generics turned into, in the order they were generated. Like a lifted clause they are ordinary functions from here down — but unlike one they are reached *by name* from arbitrary call sites, so they carry no [fparent] and a dev build gives each its own cell. *) let fns = fns @ List.rev env.instances in (* Sorted, so the emitted IR is reproducible build to build: a Hashtbl's fold order is not. *) let values name tbl = Hashtbl.fold (fun _ v acc -> v :: acc) tbl [] |> List.sort (fun a b -> String.compare (name a) (name b)) in let externs = Hashtbl.fold (fun name esym acc -> let eparams, eret = Hashtbl.find env.fns name in { Tast.ename = name; esym; eparams; eret } :: acc) env.externs [] |> List.sort (fun (a : Tast.extern) b -> String.compare a.Tast.esym b.Tast.esym) in ({ Tast.structs = values (fun (s : Tast.structure) -> s.Tast.sname) env.structs; datas = values (fun (u : Tast.data) -> u.Tast.dname) env.datas; unions = values (fun (u : Tast.structure) -> u.Tast.sname) env.unions; globals; externs; fns; cshim }, env) (** The program and the environment, stopping at the first refusal. What a session needs, and it raises [Loc.Error] and never [Loc.Errors]. *) let program_with_env (decls : Ast.decl list) : Tast.program * env = build_program ~keep_going:false decls let program (decls : Ast.decl list) : Tast.program = fst (build_program ~keep_going:false decls) (** The same, reporting every declaration whose body it refuses rather than the first. Raises [Loc.Errors], so only a caller prepared for a list should be calling it. *) let program_all (decls : Ast.decl list) : Tast.program = fst (build_program ~keep_going:true decls) (* ── What a session needs to know about instantiations ────────────────── A generic [defn] never reaches [Tast.fns] — only its copies do — so the editor's [C-c C-c], which installs the bodies named by the form it was sent, would install nothing at all for a generic. These are what [Session.eval] expands the name with. They are here rather than there because [env]'s tables are the only record that a symbol was ever generic: past this module an instantiation is an ordinary function and nothing knows it was written once. *) (* Is this name a generic definition rather than an ordinary one? *) let is_generic env n = Hashtbl.mem env.gsigs n (* Every copy of [gname] this check produced, by symbol. Transitivity needs no walk: a whole-program check has already generated every copy every call site asked for, including the ones a generic pulled in by calling another generic at its own variable. *) let instantiations env gname = match Hashtbl.find_opt env.insts gname with | None -> [] | Some l -> List.rev_map (fun (_, _, sym) -> sym) !l (* The generic a symbol came from, and the types it was asked for — [None] for an ordinary function. What a refusal about [sort!-i32] needs in order to say which line the programmer should look at, since [sort!-i32] appears nowhere in the source. *) let instantiation_origin env sym = Hashtbl.fold (fun gname l acc -> match acc with | Some _ -> acc | None -> (match List.find_opt (fun (_, _, s) -> String.equal s sym) !l with | Some (ps, _, _) -> Some (gname, ps) | None -> None)) env.insts None (* Checking one expression against a live session can *generate* a copy: the first [C-x C-e] of [(id 3)] instantiates [id] at [i32] and the copy is in [env.instances] and in no program anywhere. Without these two the module that gets built calls a symbol it never defined. A mark before and the difference after is the whole protocol. *) let instance_mark env = List.length env.instances let instances_since env mark = let fresh = List.length env.instances - mark in List.rev (List.filteri (fun i _ -> i < fresh) env.instances) (* One expression, checked against a program that is already running. The frame is empty — a REPL expression has no parameters and no enclosing function — so the slots it needs are whatever its own [let]s allocate. *) let expression env (e : Ast.expr) : Tast.expr * Types.t array * string option array = let ctx = { env; ret = Types.Unit; slots = 0; slot_tys = []; slot_names = []; scope = []; defers = []; outer = []; outer_what = None; in_frames = None; loops = []; tail = false; in_defer = false; defer_ok = false; defer_block = "a nested form"; dead = []; borrow = false; owner = "" } in let t = check ctx e in (t, Array.of_list (List.rev ctx.slot_tys), Array.of_list (List.rev ctx.slot_names))