Joseph Ferano
9ce51ba94e
as-slice was a warning, not an operation. The input type already decides which of the two things happens — a Vec can only be borrowed, an array or a string can only be viewed, and no call site picks between them — so the second name expressed no choice a reader could make. And it warned at the moment the view is taken, which is the one moment nothing is wrong; the danger arrives later, at the push. slice now takes a Vec at all three arities and as-slice is gone. (slice v lo) was free, and is the arity the Vec never had: the runtime already reads a hi of -1 as "to the end", so the tail form passes the caller's lo and the same -1 — no slot, no length read, no second evaluation. The merge is entirely in the checker; the Vec path builds the flan_vec_as_slice call it always built and neither backend has a line about any of it. A Vec a call returned is refused at every arity, and not for the array's reason. (slice (mk)) over an array dangles. (slice (make-vec)) does not — the storage outlives the expression — but the header is a temporary, so nothing can ever free the block. The refusal says that and names the let. The name's own refusal sits in ordinary_call after every table, so a program that defines an as-slice still reaches its own. It reads for somebody who has never heard of the old name and writes the call back out, spelling each argument that is a name or a number. The warning moved to where it bites: BUILT.md gains a section beside the Vec table and the push row points at it, spec-memory.md's Borrowing says the same. Investigated and deliberately not built — a diagnostic for a live view at the push. (reserve v 100) then a slice, a push and a read is correct code under the contract the spec chose, so any flag on it is a false positive by the language's own semantics rather than by an approximation. FIX.org has the finding and the syntactic sketch that does not work.
90 lines
3.5 KiB
Plaintext
90 lines
3.5 KiB
Plaintext
;;;; Computed global initialisers — plan.org, Data model.
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;;;;
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;;;; A global whose value is not something a linker can write into the image.
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;;;; The initialiser is lifted into a function of its own and called at startup,
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;;;; from main, after the runtime is up and before a line of the program's own
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;;;; code — Odin's __$startup_runtime shape rather than a constructor. Both
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;;;; backends do it the same way, which is what the x86 survey is comparing.
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;;;;
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;;;; What each half of this file is asserting:
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;;;;
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;;;; - an arena allocated at startup and used from main, which is the form
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;;;; the author kept writing: (defonce frame Allocator (arena-new N)).
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;;;; - the order. `derived` is written above the global it reads, so the
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;;;; declaration order is the wrong one and the sort is what makes it 30.
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;;;; - a dependency that runs through a call rather than through the text of
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;;;; the initialiser: `via-fn` names no global at all, and the function it
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;;;; calls reads one.
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;;;; - control flow in an initialiser. Every one of these needs a frame, and
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;;;; before the lift there was none — a `let` in an initialiser indexed a
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;;;; slot array of length zero and took the compiler down with it.
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;;;; - a container loaded by its own initialiser, and a data type case
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;;;; written into a global. Both were refused while there was nowhere for
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;;;; an initialiser to run.
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(defdata Shape [Nothing (Circle [r i32]) (Square [side i32])])
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;; Written above `base`, and it reads it.
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(defonce derived i64 (* base 10))
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(defonce base i64 (+ 1 2))
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(defn twice-base [] i64 (* base 2))
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;; Names no global; the function it calls does.
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(defonce via-fn i64 (+ (twice-base) 1))
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;; The author's arena, and the Vec it is meant to hold.
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(defonce frame Allocator (arena-new 262144))
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;; Control flow, each shape in its own global.
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(defn maybe [] (Option i32) (Some 3))
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(defonce matched i32 (match (maybe) (Some x) x None 0))
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(defonce branched i64 (if (> base 2) (let [k (+ base 1)] (* k 2)) 0))
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(defonce counted i64 (let [t (i64 0)] (while (< t 4) (set t (+ t 1))) t))
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;; A data type case: a store at startup, where a constant would have needed a
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;; byte-level encoder for the payload blob.
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(defonce shape Shape (Shape.Circle {.r 7}))
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;; And a container whose real value only exists behind an allocator.
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(defonce names (Vec i64) (vec-new i64))
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;; [def], the re-run form, in a plain run — where there is no re-run, so each
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;; is simply its initialiser's value. What these four pin is that every
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;; spelling lowers and starts identically on both backends, with the
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;; initialiser lifted into [global/<n>] whatever it is (a def's always is,
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;; zero and literal included) rather than written into the image.
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(def d-zero [2 u32])
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(def d-typed i64 (+ base 2))
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(def d-const i64 5)
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(def d-dyn 6)
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(defn main [] i32
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(println derived)
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(println base)
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(println via-fn)
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(println matched)
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(println branched)
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(println counted)
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(match shape
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(Circle r) (println r)
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(Square s) (println s)
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Nothing (println -1))
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;; The Vec was made with the default allocator at startup and is still the
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;; program's when main runs.
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(push names 11)
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(push names 22)
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(println (len (slice names)))
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(println (at names 1))
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(free names)
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;; And the arena, used the way sand.flan means to use it.
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(with-allocator frame
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(let [v (vec-new i64)]
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(push v 7)
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(println (at v 0))))
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(free-all frame)
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(println (i32 (at d-zero 0)))
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(println d-typed)
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(println d-const)
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(println d-dyn)
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0)
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