diff --git a/TODO.org b/TODO.org
index 3ea45b08..5ab4afe7 100644
--- a/TODO.org
+++ b/TODO.org
@@ -73,11 +73,13 @@ is wrong where it was written rather than aborting the compile with no location.
 The prelude's own =unless= has not been converted and still answers a bare
 undefined name.
 
-** TODO gensym's counter restarts in a second module
-The counter lives in the loaded module and a module is dlopened once per compiler
-process, so it is process-wide in practice — but the rounds already build more
-than one module for a program whose macros call macros. Seed it from the module's
-index.
+** DONE gensym's counter restarts in a second module
+CLOSED: [2026-09-25]
+The counter is C data in the runtime (=flan_gensym_n=), and =lib/macro.ml= writes
+the compiler's own count into the module before every macro call and reads it
+back after. It counts across every module a compiler process loads — each round,
+the program's module, and every expansion in a session. Rules out a counter per
+module, seeded or not.
 
 ** TODO A quasiquote inside a quasiquote is refused
 Nothing counts nesting levels — not the reader, deliberately, and not the
@@ -141,11 +143,18 @@ as words the reader will not read back. =(/ 1.0 0.0)= is the only route to an
 infinity, and the constant folder is integers only, so it cannot be a =defconst=.
 Closing it needs a reader literal or a float-capable folding pass.
 
-** TODO A u64 constant above 2^63 cannot be written in decimal
-The reader reads a decimal integer literal as a signed 64-bit number; hex is read
-as a bit pattern and works. The same limit has a second face: a cast's argument is
-checked against the default type, so =(u64 2935910691)= is refused for not fitting
-in an =i32=.
+** DONE A u64 constant above 2^63 cannot be written in decimal
+CLOSED: [2026-09-25]
+An integer written at or above 2^63 — a decimal up to 2^64 - 1, or hex with the
+top bit set — reads as =Form.UInt=, its pattern and its spelling. It is accepted
+where the type is =u64=, a =(u64 ...)= cast included, and refused everywhere else
+in the spelling it was written in. Hex with the top bit set was accepted as a
+negative at any integer type before this; it is refused now too. A negative
+decimal is still a =u64= bit pattern. A cast's integer literal that does not fit
+=i32= is checked at the cast's type; one that fits keeps the =i32= default, so
+=(u32 -1)= still means what it did. A wide literal that passes through a macro
+comes back as an ordinary =Int=, because the macro side's =Form= has one integer
+case. Rules out a second integer case in the prelude's =Form=.
 
 ** DONE {.row .col} binds same-named locals
 CLOSED: [2026-09-20]
@@ -790,14 +799,11 @@ program that does not type-check. Moot for anything that compiles; only the
 daemon's half-typed recompiles could feel it. A cheaper retry was tried and
 shelved because it changes which literal gets the nicer message.
 
-** TODO and's last operand gets a misdirected caret
-=(println (and true true (vec-new i32)))= puts the caret on the second =true=. The
-last operand of an =and= is the then arm and the then arm is typed first, so the
-mismatch is blamed on the else arm, which carries the previous operand's location.
-The fix is preferring the arm that is not a compiler temp when deciding whom to
-blame. Three others were considered and rejected: relabelling the else arm reads
-backwards, a bool sentinel reverts the =or= fix, and inverting the condition costs
-a =not= per operand.
+** DONE and's last operand gets a misdirected caret
+CLOSED: [2026-09-25]
+Already fixed by 3672da2, which blames the arm that is not a compiler temp; the
+caret is on the last operand and =test/test_flan.ml= asserts its column. Rules
+out relabelling the else arm, a bool sentinel, and inverting the condition.
 
 ** TODO Signature pairing's cold-rebuild edge
 Whether a parameter vector reads as one annotated parameter or two dyn ones
@@ -841,14 +847,21 @@ Iteration is built; the remaining refusal is generics. A =defn= has to name its
 types and =(defn map-keys [m (Map K V)] (Vec K))= has no =K=. The loop is three
 lines at the call site, where =K= is known.
 
-** TODO (vec-new [u8]) is refused
-The element type must be a bare symbol naming a type, so a =(Vec [u8])= can only
-be made where the context names it. The fix is letting it take a type expression —
-the same parser that already reads =[u8]= in a parameter list.
+** DONE (vec-new [u8]) is refused
+CLOSED: [2026-09-25]
+The type positions of =vec-new= and =map-new= take a type expression: brackets, or
+a parenthesised =Ptr=, =Option=, =Vec=, =Map=, =Fn= or =CFn=. The arguments stay
+ordinary expressions and the builtin reads the type back out of one
+(=Check.type_of_expr=), so a program's own =vec-new= still gets values; only a
+type an expression cannot hold, such as =(Fn [i32] ())=, is parsed as
+=Ast.TypeArg=. Rules out a type expression anywhere else in expression position.
 
 ** TODO An array literal cannot say it is [f32]
 A float literal defaults to =f64=, an array literal has no context, and a =let=
 has no annotation. Same shape as =(vec-new [u8])= and probably the same fix.
+Not the same fix: a bracket literal has no argument to put a type in. Decision:
+how a literal names its element type — a spelling of its own, or a =let=
+annotation.
 
 ** TODO A let binding takes no type annotation
 Everything under the surface is there — the binding carries a type slot and the
@@ -1860,12 +1873,12 @@ instrumented copy; the equivalent here is a dev-build-only instrumented
 redefinition, which the cell indirection already makes deliverable. Open:
 whether stepping suspends the frame loop, and what it does to a game's clock.
 
-** TODO A NaN cast says "does not fit", which reads as too big
-=runtime/flan_rt.c:1008= covers every out-of-range float with one sentence, so
-=(i32 nan)= reports the =i32= bounds as if the value had overshot them. NaN and
-the infinities convert to no integer at all and want saying so by name. Found
-by filling a struct holding an =f32= with =(filled 0xFF)=, where every bit set
-is NaN.
+** DONE A NaN cast says "does not fit", which reads as too big
+CLOSED: [2026-09-25]
+Two more =ArithError= codes: 5 for a cast of NaN and 6 for a cast of an infinity,
+each with its own sentence. Both backends choose the code on the cold path, so the
+guard is still two compares. =lhs= and =rhs= still carry the range. Rules out
+carrying the float value in the condition.
 
 ** TODO The break buffer prints fields, not the sentence the runtime wrote
 =ArithError — op 4, lhs -2147483648, rhs 2147483647= where the runtime's own
@@ -1892,12 +1905,12 @@ when it opens, so =M-g M-n= walks the stop and then each frame with a file.
 Refusals — the prelude, a relative path, a missing file — are one function
 shared with =M-.=.
 
-** TODO loop's bindings should be sequential, like let's
-=check_loop= (=lib/check.ml:4741=) checks every initialiser before binding any,
-so =(loop [curr-r r  next-r (inc curr-r)] ...)= cannot see =curr-r= and the
-refusal reads as an unknown name. Every binding form is sequential — there is
-no =let*= here and there is not going to be one. Check the other binding forms
-for the same gap while fixing it.
+** DONE loop's bindings should be sequential, like let's
+CLOSED: [2026-09-25]
+=check_loop= binds each name before checking the next initialiser; =recur= still
+rebinds all at once. No other form had the gap: =let= was already sequential,
+=dotimes= binds one name, and =fn=, =defn=, =match= and the handler and restart
+clauses bind parameters with no initialisers.
 
 ** TODO C-c C-c reports one error, not every error in the form
 Whole-file paths use =Check.program_all= and report every bad declaration. The
diff --git a/lib/ast.ml b/lib/ast.ml
index c49e9e36..f3677360 100644
--- a/lib/ast.ml
+++ b/lib/ast.ml
@@ -36,6 +36,7 @@ type expr = { e : expr_kind; loc : Loc.t }
 
 and expr_kind =
   | Int    of int64
+  | UInt   of int64 * string          (* 18446744073709551615 — u64 only *)
   | Float  of float
   | Byte   of int
   | Str    of string
@@ -97,6 +98,12 @@ and expr_kind =
      fails on an unknown name. This is that position's answer, and it says what
      it does rather than looking like a vector of two things. *)
   | ArrayOf of texpr                  (* the whole array type, built by Parse *)
+  (* (vec-new [u8]) and (map-new string [u8]) — a type written where an
+     argument goes. Only the type positions of those two forms read one, and
+     only when the form's shape says type and not value: brackets, or a
+     parenthesised Ptr, Option, Vec, Map, Fn or CFn. A bare name stays a
+     [Var], which the checker already answers as a type. *)
+  | TypeArg of texpr
   (* (array-fill [r c] v) and (array-gen [r c] f) — a fixed array of any rank
      as an *expression*, which is what [ArrayOf] and [dotimes] between them
      could not be: [ArrayOf] produces the zeroed value only, and [dotimes] is
@@ -402,8 +409,8 @@ let map_children f (e : expr) : expr =
   in
   let kind =
     match e.e with
-    | Int _ | Float _ | Byte _ | Str _ | Kw _ | Quote _ | Var _ | ArrayOf _
-    | Break _ | Continue _ -> e.e
+    | Int _ | UInt _ | Float _ | Byte _ | Str _ | Kw _ | Quote _ | Var _ | ArrayOf _
+    | TypeArg _ | Break _ | Continue _ -> e.e
     | Do es -> Do (List.map ex es)
     | Let (bs, es) -> Let (List.map bind bs, List.map ex es)
     | If (c, a, b) -> If (ex c, ex a, Option.map ex b)
diff --git a/lib/check.ml b/lib/check.ml
index a127a542..f81e1479 100644
--- a/lib/check.ml
+++ b/lib/check.ml
@@ -395,6 +395,7 @@ let spell_arg stand_for (a : Ast.expr) =
   match a.Ast.e with
   | Ast.Var v -> v
   | Ast.Int n -> Int64.to_string n
+  | Ast.UInt (_, s) -> s
   | _ -> stand_for
 
 (* What a [break] or a [continue] may be talking about, innermost first.
@@ -1958,7 +1959,9 @@ let check_fn_ref : (env -> Ast.fn -> Tast.fn) ref =
 (* 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
+  match e.Ast.e with
+  | Ast.Int _ | Ast.UInt _ | 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. *)
@@ -3317,6 +3320,7 @@ let rec check ctx ?want (e : Ast.expr) : Tast.expr =
   ctx.tail <- false;
   match e.Ast.e with
   | Ast.Int n -> int_literal loc ~want ~preds:ctx.env.tvpreds n
+  | Ast.UInt (n, s) -> wide_literal loc ~want n s
   | Ast.Byte b ->
     int_literal loc ~want ~preds:ctx.env.tvpreds ~default:Types.U8
       (Int64.of_int b)
@@ -3567,6 +3571,11 @@ let rec check ctx ?want (e : Ast.expr) : Tast.expr =
   | Ast.ArrayOf t ->
     let ty = resolve ctx.env t in
     expect ctx loc ~want (mk loc ty (Tast.Zero ty))
+  (* Parse writes one only into a type position of a call named vec-new or
+     map-new, and the builtins read it before it could get here. A program's
+     own function of that name does not. *)
+  | Ast.TypeArg _ ->
+    fail loc "this is a type, and a value is wanted here"
   | Ast.ArrayFill (dims, v) -> check_array_fill ctx ~want loc dims v
   | Ast.ArrayGen (dims, f) -> check_array_gen ctx ~want loc dims f
   | Ast.Match (scrutinee, arms) -> check_match ctx ~tail ?want loc scrutinee arms
@@ -3747,6 +3756,29 @@ and int_literal loc ~want ?(preds = []) ?(default = Types.I32) n =
       (Types.to_string other) n
   | _ -> mk loc (Types.Int default) (Tast.Int (in_range loc default n, default))
 
+(* An integer written at or above 2^63, in decimal or in hex. Only a u64 holds
+   one, so it is accepted there and refused everywhere else, in the spelling it
+   was written in — its pattern read as an i64 is a different number. *)
+and wide_literal loc ~want n s =
+  match want with
+  | Some (Types.Int Types.U64) -> mk loc (Types.Int Types.U64) (Tast.Int (n, Types.U64))
+  | Some (Types.Int k) ->
+    Loc.failk literal_at_want loc "%s does not fit in %s" s (Types.ikind_name k)
+  | Some (Types.Float _ as t) ->
+    Loc.failk literal_at_want loc
+      "%s is too large for any integer type but u64, and an integer literal \
+       where %s is wanted is read as one — write (%s (u64 %s))"
+      s (Types.to_string t) (Types.to_string t) s
+  | Some Types.Never | None ->
+    Loc.failk literal_at_want loc
+      "%s does not fit in i32, the type an integer literal takes when nothing \
+       says otherwise — write (u64 %s) for a u64"
+      s s
+  | Some other ->
+    Loc.failk literal_at_want loc
+      "expected %s, found the integer literal %s, which only a u64 holds"
+      (Types.to_string other) s
+
 (* 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 =
@@ -3757,13 +3789,10 @@ and in_range loc k n =
       || (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. *)
+      (* A literal at or above 2^63 is a [UInt] and never reaches here; see
+         [wide_literal]. A negative decimal is accepted as a u64's bit pattern,
+         which is a settled rule. 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
@@ -4757,8 +4786,10 @@ and check_dotimes ctx ~want loc label name (b : Ast.bounds) body =
 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 =
+       [let]'s is and as [dotimes]'s bound is — and bound before the next is
+       checked, as a [let]'s is, so a later initialiser sees an earlier
+       name. *)
+    let binds =
       map_lr
         (fun (n, v) ->
            let v = check ctx v in
@@ -4767,12 +4798,9 @@ and check_loop ctx ?want loc bs body =
               fail v.Tast.loc "%s would be bound to %s, which is not a value" n
                 (Types.to_string v.Tast.ty)
             | _ -> ());
-           (n, v))
+           (bind ctx n v.Tast.ty ~assignable:true, 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. *)
@@ -6585,12 +6613,16 @@ and type_named ctx 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. *)
+(* The element type for [vec-new]: a leading bare symbol naming a type, a
+   leading type expression — [(vec-new [u8])], [(vec-new (Ptr Cell))], which
+   Parse has already read as one — 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
+    | a :: rest when type_of_expr a <> None ->
+      Some (resolve ctx.env (Option.get (type_of_expr a)), rest)
     | { Ast.e = Ast.Var n; _ } :: rest
       when lookup ctx n = None
         && (not (Hashtbl.mem ctx.env.globals n))
@@ -6608,6 +6640,39 @@ and vec_new_elem ctx ~want loc args =
          "nothing here says what (vec-new) is a Vec of — write the element \
           type, as (vec-new i32), or give the binding a type")
 
+(* A type written as an argument to vec-new or map-new, read back out of the
+   expression Parse made of it. Only the shapes that cannot be a value there:
+   brackets — an allocator is never an array — or a parenthesised Ptr,
+   Option, Vec, Map, Fn or CFn. A bare name is not one of them, because there
+   it may be an allocator's name; the callers ask about that themselves. *)
+and type_of_expr (e : Ast.expr) : Ast.texpr option =
+  let mk t = { Ast.t; tloc = e.Ast.loc } in
+  let inner (e : Ast.expr) =
+    match e.Ast.e with
+    | Ast.Var s -> Some { Ast.t = Ast.Tname s; tloc = e.Ast.loc }
+    | _ -> type_of_expr e
+  in
+  let all es =
+    let ts = List.filter_map inner es in
+    if List.length ts = List.length es then Some ts else None
+  in
+  match e.Ast.e with
+  | Ast.TypeArg t -> Some t
+  | Ast.Arr [ x ] -> Option.map (fun t -> mk (Ast.Tslice t)) (inner x)
+  | Ast.Arr [ { Ast.e = Ast.Int n; _ }; x ] ->
+    Option.map (fun t -> mk (Ast.Tarray (Ast.Lint n, t))) (inner x)
+  | Ast.Arr [ { Ast.e = Ast.Var n; _ }; x ] ->
+    Option.map (fun t -> mk (Ast.Tarray (Ast.Lname n, t))) (inner x)
+  | Ast.Call ({ Ast.e = Ast.Var (("Fn" | "CFn") as which); _ },
+              [ { Ast.e = Ast.Arr ps; _ }; r ]) ->
+    (match all ps, inner r with
+     | Some ps, Some r -> Some (mk (Ast.Tfn (which = "Fn", ps, r)))
+     | _ -> None)
+  | Ast.Call ({ Ast.e = Ast.Var (("Ptr" | "Option" | "Vec" | "Map") as c); _ },
+              (_ :: _ as args)) ->
+    Option.map (fun ts -> mk (Ast.Tapp (c, ts))) (all args)
+  | _ -> None
+
 (* The key and value types, or the reason this is not a Map. *)
 and map_kv loc what (t : Types.t) =
   match t with
@@ -6625,10 +6690,21 @@ and map_new_types ctx ~want loc args =
     && (not (Hashtbl.mem ctx.env.globals n))
     && type_named ctx n
   in
+  (* A type position holds a bare name or a type expression Parse has read
+     as one, as [vec-new]'s does. *)
+  let as_type (a : Ast.expr) =
+    match a.Ast.e, type_of_expr a with
+    | _, Some t -> Some (resolve ctx.env t)
+    | Ast.Var n, None when is_type n -> Some (resolve_name ctx.env ~seen:[] loc n)
+    | _ -> None
+  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
+  | k :: v :: rest when as_type k <> None && as_type v <> None ->
+    Option.get (as_type k), Option.get (as_type v), rest
+  | a :: _ when type_of_expr a <> None ->
+    fail loc
+      "(map-new) names a key and no value — write both, as (map-new string \
+       i32), or give the binding a type"
   | { 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 \
@@ -8858,7 +8934,19 @@ and named_call ?(qualified = false) ctx ~want loc name args =
     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
+    (* An integer literal too wide for the i32 it would default to is checked
+       at the target instead, so (u64 2935910691) and (i64 5000000000) are the
+       constants they say. One that fits i32 keeps the default and the cast,
+       which is what (u32 -1) has always meant. *)
+    let want =
+      match (List.hd args).Ast.e, target with
+      | Ast.Int n, (Types.Int _ | Types.Float _)
+        when Int64.compare n (-2147483648L) < 0
+             || Int64.compare n 2147483647L > 0 -> Some target
+      | Ast.UInt _, (Types.Int _ | Types.Float _) -> Some target
+      | _ -> None
+    in
+    let a = check ctx ?want (List.hd args) in
     (match a.Tast.ty with
      | Types.Enum _ -> ()
      (* A dyn opens here — [cast_dyn], TODO.org, "A numeric cast opens a dyn
@@ -9181,7 +9269,7 @@ and generic_call ctx ~want loc name vars pats pret args =
             else is checked on its own terms. *)
          let untyped_literal =
            match a.Ast.e with
-           | Ast.Int _ | Ast.Float _ | Ast.Byte _ -> true
+           | Ast.Int _ | Ast.UInt _ | Ast.Float _ | Ast.Byte _ -> true
            | _ -> false
          in
          let a =
@@ -9653,7 +9741,7 @@ and binary ctx ?(dyn_ok = false) ?(join = true) name loc ~want args =
     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
+          | (Ast.Int _ | Ast.UInt _ | Ast.Byte _), Ast.Float _ -> true
           | _ -> false)
     in
     (* A form that cannot be checked without being told what is wanted. A
diff --git a/lib/emit.ml b/lib/emit.ml
index c4d380e9..4b49fb25 100644
--- a/lib/emit.ml
+++ b/lib/emit.ml
@@ -1517,6 +1517,8 @@ let arith_rem_zero = 1
 let arith_div_overflow = 2
 let arith_rem_overflow = 3
 let arith_cast_range = 4
+let arith_cast_nan = 5
+let arith_cast_inf = 6
 
 (* ArithError's fields are i64 and an operand may be narrower, so every
    operand is widened on the way into the condition — signed or not according
@@ -1668,11 +1670,27 @@ let check_cast f ~guard loc (src : Types.fkind) (k : Types.ikind) v =
     ins f "%s = fcmp olt double %s, %s" b v (dbl hi_f);
     let ok = fresh f in
     ins f "%s = and i1 %s, %s" ok a b;
+    (* NaN and the infinities are named rather than reported as out of range:
+       they are not values that overshot the type, they have no integer at
+       all. Worked out on the cold path, so the guard is still two compares. *)
     signal_block f loc ~guard ok (fun id nn ->
+      let nan = fresh f in
+      ins f "%s = fcmp uno double %s, %s" nan v v;
+      let pinf = fresh f in
+      ins f "%s = fcmp oeq double %s, %s" pinf v (dbl infinity);
+      let ninf = fresh f in
+      ins f "%s = fcmp oeq double %s, %s" ninf v (dbl neg_infinity);
+      let inf = fresh f in
+      ins f "%s = or i1 %s, %s" inf pinf ninf;
+      let c1 = fresh f in
+      ins f "%s = select i1 %s, i32 %d, i32 %d" c1 inf arith_cast_inf
+        arith_cast_range;
+      let code = fresh f in
+      ins f "%s = select i1 %s, i32 %d, i32 %s" code nan arith_cast_nan c1;
       ins f
-        "call void @flan_arith_error(ptr %s, i64 %d, i32 %d, i64 %Ld, i64 %Ld, \
+        "call void @flan_arith_error(ptr %s, i64 %d, i32 %s, i64 %Ld, i64 %Ld, \
          ptr %s)"
-        id nn arith_cast_range lo_i hi_i xfer_param)
+        id nn code lo_i hi_i xfer_param)
   end
 
 (* [at] is strict: the last valid index is len - 1. *)
diff --git a/lib/expand.ml b/lib/expand.ml
index 017bfe73..98bbfe94 100644
--- a/lib/expand.ml
+++ b/lib/expand.ml
@@ -114,6 +114,9 @@ let rec write (sites : sites) p (f : Form.t) =
   | Form.Kw s -> str TKw s
   | Form.Str s -> str TStr s
   | Form.Int i -> tag TInt; Dynload.poke_i64 p payload i
+  (* A macro's Form has one integer case, so a wide literal crosses as its
+     pattern and comes back as an ordinary [Int]. *)
+  | Form.UInt (i, _) -> tag TInt; Dynload.poke_i64 p payload i
   | Form.Float x -> tag TFloat; Dynload.poke_f64 p payload x
   | Form.Byte b -> tag TByte; Dynload.poke_i32 p payload (Int32.of_int b)
   | Form.List xs -> seq TList xs
@@ -251,7 +254,7 @@ let rec quote (f : Form.t) : Form.t =
            inner form with form-cons"
       | Form.Sym s -> node loc "Sym" "s" (Form.Str s)
       | Form.Kw s -> node loc "Kw" "s" (Form.Str s)
-      | Form.Int i -> node loc "Int" "i" (Form.Int i)
+      | Form.Int i | Form.UInt (i, _) -> node loc "Int" "i" (Form.Int i)
       | Form.Float x -> node loc "Float" "x" (Form.Float x)
       | Form.Str s -> node loc "Str" "s" (Form.Str s)
       | Form.Byte b -> node loc "Byte" "b" (Form.Int (Int64.of_int b))
diff --git a/lib/form.ml b/lib/form.ml
index b16ace01..2eda0357 100644
--- a/lib/form.ml
+++ b/lib/form.ml
@@ -12,6 +12,10 @@ and value =
   | Sym   of string        (* foo  rl/draw-fps  .pos  + *)
   | Kw    of string        (* :space  :else                    (leading : dropped) *)
   | Int   of int64         (* 42  -1  0xE6B800FF *)
+  (* An integer written at or above 2^63 — 18446744073709551615, or a hex
+     literal with its top bit set. Its 64-bit pattern and its spelling: only a
+     u64 holds it, and a refusal anywhere else prints the number as written. *)
+  | UInt  of int64 * string
   | Float of float         (* 0.05 *)
   | Str   of string        (* "SAND" *)
   | Byte  of int           (* \space  \0  \(                   (0..255) *)
@@ -30,6 +34,7 @@ let rec to_string f =
   | Sym s   -> s
   | Kw s    -> ":" ^ s
   | Int i   -> Int64.to_string i
+  | UInt (_, s) -> s
   | Float x -> Printf.sprintf "%g" x
   | Str s   -> Printf.sprintf "%S" s
   | Byte b  ->
@@ -126,6 +131,7 @@ let rec to_source f =
   | Sym s -> s
   | Kw s -> ":" ^ s
   | Int i -> Int64.to_string i
+  | UInt (_, s) -> s
   | Float x -> float_repr x
   | Str s -> "\"" ^ escape s ^ "\""
   | Byte b -> byte_repr b
diff --git a/lib/load.ml b/lib/load.ml
index 96629722..cac0d6c6 100644
--- a/lib/load.ml
+++ b/lib/load.ml
@@ -223,7 +223,7 @@ let rec rename_expr owned alias bound (e : Ast.expr) : Ast.expr =
   let name n = qualify_name owned alias bound n in
   let k =
     match e.Ast.e with
-    | Ast.Int _ | Ast.Float _ | Ast.Byte _ | Ast.Str _ | Ast.Kw _
+    | Ast.Int _ | Ast.UInt _ | Ast.Float _ | Ast.Byte _ | Ast.Str _ | Ast.Kw _
     | Ast.Quote _ -> e.Ast.e
     | Ast.Var n -> Ast.Var (name n)
     | Ast.Do body -> Ast.Do (gos body)
@@ -307,6 +307,7 @@ let rec rename_expr owned alias bound (e : Ast.expr) : Ast.expr =
       Ast.MapLit (tag, List.map (fun (k, v) -> (go k, go v)) kvs)
     | Ast.Arr items -> Ast.Arr (gos items)
     | Ast.ArrayOf t -> Ast.ArrayOf (rename_texpr owned alias t)
+    | Ast.TypeArg t -> Ast.TypeArg (rename_texpr owned alias t)
     (* The dimensions too, for the reason [rename_texpr] gives about the one
        inside [Tarray]: a dimension written as a name is an ordinary
        compile-time constant of the package and has to be qualified like any
@@ -753,7 +754,8 @@ let rec expr_uses acc (e : Ast.expr) =
   let go = expr_uses acc in
   let gos = List.iter go in
   match e.Ast.e with
-  | Ast.Int _ | Ast.Float _ | Ast.Byte _ | Ast.Str _ | Ast.Kw _ | Ast.Quote _ ->
+  | Ast.Int _ | Ast.UInt _ | Ast.Float _ | Ast.Byte _ | Ast.Str _ | Ast.Kw _
+  | Ast.Quote _ ->
     ()
   (* The name is not one an import can supply, but the arguments are ordinary
      expressions and may well use one. *)
@@ -787,7 +789,7 @@ let rec expr_uses acc (e : Ast.expr) =
   | Ast.Bare kvs -> List.iter (fun (_, v) -> go v) kvs
   | Ast.MapLit (_, kvs) -> List.iter (fun (k, v) -> go k; go v) kvs
   | Ast.Arr items -> gos items
-  | Ast.ArrayOf t -> texpr_uses acc t
+  | Ast.ArrayOf t | Ast.TypeArg t -> texpr_uses acc t
   (* A dimension written as a name is a use of that constant, exactly as it is
      inside [Tarray]. *)
   | Ast.ArrayFill (ds, v) | Ast.ArrayGen (ds, v) ->
diff --git a/lib/macro.ml b/lib/macro.ml
index 177b4c34..b31ed83a 100644
--- a/lib/macro.ml
+++ b/lib/macro.ml
@@ -380,12 +380,28 @@ let dir_of (l : loaded) (loc : Loc.t) =
    always has a signature, and the one thing that could put a name in [fns]
    without one is the two lists coming apart — in which case expanding
    unchecked is the wrong half to lose. *)
+(* The gensym counter, process-wide. Every module links its own runtime and
+   so its own [flan_gensym_n], and a build loads several — one per round when
+   a macro calls a macro, then the one the program is expanded with, and a
+   session loads one per expansion. A counter that restarted in each would
+   hand a later module the name an earlier one had already baked into a
+   macro's code. So the count lives here and is written into the module
+   before every call and read back after, whether the call returns or
+   raises. *)
+let gensym_n = ref 0L
+
+let with_gensym (l : loaded) f =
+  let cell = Dynload.dl_sym l.handle "flan_gensym_n" in
+  Dynload.poke_i64 cell 0 !gensym_n;
+  Fun.protect ~finally:(fun () -> gensym_n := Dynload.peek_i64 cell 0) f
+
 let checked_call (l : loaded) n ~loc (args : Form.t list) : Form.t =
   (match List.assoc_opt n l.sigs with
    | Some sg -> Expand.check_call ~name:n ~loc sg args
    | None -> ());
   dir_of l loc;
-  Expand.call ~loc:(Loc.from_macro n loc) (List.assoc n l.fns) args
+  with_gensym l (fun () ->
+    Expand.call ~loc:(Loc.from_macro n loc) (List.assoc n l.fns) args)
 
 let fuel = 200
 
diff --git a/lib/parse.ml b/lib/parse.ml
index 456c8a8b..acc61a0f 100644
--- a/lib/parse.ml
+++ b/lib/parse.ml
@@ -310,6 +310,7 @@ let rec expr (f : Form.t) : Ast.expr =
   let mk e = { Ast.e; loc = f.loc } in
   match f.v with
   | Int i -> mk (Ast.Int i)
+  | UInt (i, s) -> mk (Ast.UInt (i, s))
   | Float x -> mk (Ast.Float x)
   | Byte b -> mk (Ast.Byte b)
   | Str s -> mk (Ast.Str s)
@@ -425,6 +426,31 @@ and form f mk (head : Form.t) (args : Form.t list) : Ast.expr =
      | [ target; value ] -> mk (Ast.Set (place target, expr value))
      | _ -> fail f "set is (set place value)")
 
+  (* ── (vec-new [u8]) and (map-new string [u8]) ───────────────────────
+     The type positions of these two take a type expression. Whether this call
+     is the builtin at all is the checker's to know — a program may define its
+     own [vec-new] — so the arguments are read as ordinary expressions and
+     [Check.type_of_expr] reads a type back out of one when the builtin is
+     what was called. The one type an expression cannot carry is [()], as in
+     [(Fn [i32] ())], so an argument that is not an expression but is a type
+     is kept as a [TypeArg]. *)
+  | Sym (("vec-new" | "builtin/vec-new" | "map-new" | "builtin/map-new") as n) ->
+    let slots =
+      if n = "vec-new" || n = "builtin/vec-new" then 1 else 2
+    in
+    let args =
+      List.mapi
+        (fun i (a : Form.t) ->
+           match expr a with
+           | e -> e
+           | exception (Loc.Error _ as not_expr) when i < slots ->
+             (match texpr a with
+              | t -> { Ast.e = Ast.TypeArg t; loc = a.loc }
+              | exception Loc.Error _ -> raise not_expr))
+        args
+    in
+    mk (Ast.Call (expr head, args))
+
   (* ── (array 4 rl/Vector2) ───────────────────────────────────────────
      A zeroed fixed array, told its count and its element type. The type
      spelling [4 rl/Vector2] is unchanged and still works everywhere a type is
diff --git a/lib/prelude.ml b/lib/prelude.ml
index ee7e83e9..29dbfe74 100644
--- a/lib/prelude.ml
+++ b/lib/prelude.ml
@@ -123,9 +123,11 @@ let source = {flan|
 ;;   0  (/ a 0)      1  (% a 0)
 ;;   2  (/ min -1)   3  (% min -1)
 ;;   4  a float to integer cast whose value does not fit
+;;   5  a float to integer cast of NaN
+;;   6  a float to integer cast of an infinity
 ;;
 ;; `lhs` and `rhs` are the two operands for codes 0 through 3 and the
-;; destination type's representable range for code 4 — the violated condition
+;; destination type's representable range for codes 4 through 6 — the violated condition
 ;; written as a range, which is what flan_slice_promise_error already does
 ;; with BoundsError's fields. Two meanings over two fields rather than two
 ;; condition types, so that a handler writes one clause and not five. The
@@ -232,10 +234,9 @@ let source = {flan|
     ;; LLVM; at this width there is no such case to guard.
     ;;
     ;; The multiplier is written in hex, which is how it is written everywhere
-    ;; it appears: in decimal it is 12605985483714917081, and a decimal
-    ;; literal that large is refused here because the reader reads one as a
-    ;; signed 64-bit number. Hex is read as a bit pattern, and this is a bit
-    ;; pattern. It is written here rather than given a name of its own: a
+    ;; it appears: in decimal it is 12605985483714917081. Either spelling is
+    ;; a u64 literal and nothing else. It is written here rather than given a
+    ;; name of its own: a
     ;; prelude constant is a name in every program, and this is an
     ;; implementation number that nothing outside these four lines wants.
     (let [w (* (bit-xor (>> s (+ (>> s 59) 5)) s) 0xAEF17502108EF2D9)]
@@ -2135,19 +2136,19 @@ let source = {flan|
 ;; explicit gensym is the settled decision (plan.org, open decision 2); this is
 ;; the escape hatch that makes it liveable.
 ;;
-;; The counter lives in the loaded module rather than in the compiler, which is
-;; the one place this departs from the sketch. A module is dlopened once
-;; per compiler process and every macro in a program shares it, so the counter
-;; is process-wide in practice; a second module would restart it, and the day
-;; there is one, the fix is to seed this from the module's index.
-(defonce gensym-n i64 0)
+;; The counter is C data in the runtime, flan_gensym_n, because a build loads
+;; more than one macro module — one per round when macros call macros, and
+;; another for every expansion in a session — and each links its own copy of
+;; the runtime. lib/macro.ml keeps the count across them: it writes it into
+;; the module before every macro call and reads it back after, so no two
+;; modules in one compiler process draw the same name.
+(declare gensym-next [] i64 "flan_gensym_next")
 
 (defn gensym [] Form
-  (set gensym-n (+ gensym-n 1))
   (let [v (vec-new u8)]
     (push v 126)   ; ~
     (push v 103)   ; g
-    (let [d (i64->bytes gensym-n)]
+    (let [d (i64->bytes (gensym-next))]
       (dotimes [i (length d)]
         (push v (at d i))))
     (Form.Sym {.s (string (slice v))})))
diff --git a/lib/reader.ml b/lib/reader.ml
index 0e098a79..40890424 100644
--- a/lib/reader.ml
+++ b/lib/reader.ml
@@ -144,6 +144,8 @@ let read_number st =
   in
   if is_hex then
     match Int64.of_string_opt text with
+    (* A top bit set is a value at or above 2^63, which only a u64 holds. *)
+    | Some i when Int64.compare i 0L < 0 -> spanned st loc (Form.UInt (i, text))
     | Some i -> spanned st loc (Form.Int i)
     | None -> Loc.failk "reader/malformed-number" (Loc.upto loc (here st))
         "malformed hex literal %s" text
@@ -153,10 +155,20 @@ let read_number st =
     | None -> Loc.failk "reader/malformed-number" (Loc.upto loc (here st))
         "malformed float literal %s" text
   else
+    (* A decimal above the largest i64 and below 2^64 is a [UInt], as a hex
+       literal with its top bit set is: only a u64 holds it. *)
+    let unsigned () =
+      if String.for_all (fun c -> c >= '0' && c <= '9') text then
+        Int64.of_string_opt ("0u" ^ text)
+      else None
+    in
     match Int64.of_string_opt text with
     | Some i -> spanned st loc (Form.Int i)
-    | None -> Loc.failk "reader/malformed-number" (Loc.upto loc (here st))
-        "malformed integer literal %s" text
+    | None ->
+      match unsigned () with
+      | Some i -> spanned st loc (Form.UInt (i, text))
+      | None -> Loc.failk "reader/malformed-number" (Loc.upto loc (here st))
+          "malformed integer literal %s" text
 
 let read_symbol_or_keyword st =
   let loc = here st in
diff --git a/lib/x86.ml b/lib/x86.ml
index c546b4e5..b0f12a2d 100644
--- a/lib/x86.ml
+++ b/lib/x86.ml
@@ -2897,8 +2897,30 @@ and check_cast f (loc : Loc.t) (src : Types.fkind) (k : Types.ikind) =
       ucomis f.b ~f64 ~a:1 ~c:xmm0;
       jcc_lbl f.b ~cc:cc_a ok;
       lbl f.b bad;
+      (* Which code, on the cold path: NaN and the infinities are named rather
+         than reported as out of range. xmm0 still holds the value here. *)
+      let call = new_label f "nofitcall" and notnan = new_label f "notnan"
+      and isinf = new_label f "isinf" in
       imm_into f ~reg:rax (Int64.of_int Emit.arith_cast_range);
       store_int f.b ~src:rax ~mm:(Frame so) ~size:8;
+      ucomis f.b ~f64 ~a:xmm0 ~c:xmm0;
+      jcc_lbl f.b ~cc:cc_np notnan;
+      imm_into f ~reg:rax (Int64.of_int Emit.arith_cast_nan);
+      store_int f.b ~src:rax ~mm:(Frame so) ~size:8;
+      jmp_lbl f.b call;
+      lbl f.b notnan;
+      let kpinf = float_const f infinity ~f64
+      and kninf = float_const f neg_infinity ~f64 in
+      fload f.b ~dst:1 ~mm:(Sym (kpinf, 0)) ~f64;
+      ucomis f.b ~f64 ~a:xmm0 ~c:1;
+      jcc_lbl f.b ~cc:cc_e isinf;
+      fload f.b ~dst:1 ~mm:(Sym (kninf, 0)) ~f64;
+      ucomis f.b ~f64 ~a:xmm0 ~c:1;
+      jcc_lbl f.b ~cc:cc_ne call;
+      lbl f.b isinf;
+      imm_into f ~reg:rax (Int64.of_int Emit.arith_cast_inf);
+      store_int f.b ~src:rax ~mm:(Frame so) ~size:8;
+      lbl f.b call;
       imm_into f ~reg:rax lo_i;
       store_int f.b ~src:rax ~mm:(Frame sa) ~size:8;
       imm_into f ~reg:rax hi_i;
diff --git a/runtime/flan_rt.c b/runtime/flan_rt.c
index f295fa44..1332d9f6 100644
--- a/runtime/flan_rt.c
+++ b/runtime/flan_rt.c
@@ -969,7 +969,9 @@ enum {
   FLAN_ARITH_REM_ZERO = 1,
   FLAN_ARITH_DIV_OVERFLOW = 2,
   FLAN_ARITH_REM_OVERFLOW = 3,
-  FLAN_ARITH_CAST_RANGE = 4
+  FLAN_ARITH_CAST_RANGE = 4,
+  FLAN_ARITH_CAST_NAN = 5,
+  FLAN_ARITH_CAST_INF = 6
 };
 
 typedef struct { int32_t op; int64_t lhs, rhs; } flan_arith_cond;
@@ -1005,6 +1007,19 @@ static void flan_arith_fail(const uint8_t *loc, int64_t loclen, int32_t op,
             op == FLAN_ARITH_DIV_OVERFLOW ? "/" : "%", (long long)lhs,
             (long long)rhs);
     break;
+  /* NaN and the infinities did not overshoot the range: no integer is
+   * their value, whatever the type. Saying "does not fit" reads as too big. */
+  case FLAN_ARITH_CAST_NAN:
+    fprintf(stderr,
+            "%.*s: this value is NaN, which has no integer value to cast to\n",
+            (int)loclen, (const char *)loc);
+    break;
+  case FLAN_ARITH_CAST_INF:
+    fprintf(stderr,
+            "%.*s: this value is infinite, which has no integer value to cast "
+            "to\n",
+            (int)loclen, (const char *)loc);
+    break;
   default:
     fprintf(stderr,
             "%.*s: this value does not fit the integer type it is cast to, "
@@ -3181,6 +3196,14 @@ const uint8_t *flan_getenv(const uint8_t *name, int64_t n, int64_t *len) {
 char flan_macro_dir[FLAN_PATH_MAX] = { 0 };
 int64_t flan_macro_dir_n = 0;
 
+/* The prelude's gensym counter. C data rather than a Flan global for the same
+ * reason as the two above: lib/macro.ml writes it into a module before every
+ * macro call and reads it back after, which is what keeps it counting across
+ * every module a compiler process loads rather than restarting in each. */
+int64_t flan_gensym_n = 0;
+
+int64_t flan_gensym_next(void) { return ++flan_gensym_n; }
+
 /* The bytes are the caller's to read and nobody's to free: an expansion is
  * bounded by the size of the program being compiled, which is exactly the
  * budget lib/dynload.ml's `owned` note already spends on a macro's own
diff --git a/test/programs/arith-condition.flan b/test/programs/arith-condition.flan
index 62ba1381..78bd2019 100644
--- a/test/programs/arith-condition.flan
+++ b/test/programs/arith-condition.flan
@@ -180,7 +180,8 @@
 
       ;; NaN fails both halves of the range test, which is deliberate: a NaN
       ;; cast to an integer is exactly as undefined as a value out of range,
-      ;; and an unordered comparison would have waved it through.
+      ;; and an unordered comparison would have waved it through. Its code is
+      ;; 5, which names NaN, rather than 4, which says it overshot the range.
       (cast-frame (/ (f64 0.0) (f64 0.0)))
       (show "op" (i64 op))
 
diff --git a/test/programs/arith.flan b/test/programs/arith.flan
index 71b747c4..9a9d0601 100644
--- a/test/programs/arith.flan
+++ b/test/programs/arith.flan
@@ -76,6 +76,12 @@
       ;; double there, which agree because every bound is a power of two and is
       ;; exact in both.
       (= n 9) (print (i32 wide))
+      ;; NaN and the infinities have no integer value at all, so the message
+      ;; names them rather than a range they did not overshoot. An f32 source
+      ;; for each too, since the two backends test it at different widths.
+      (= n 10) (print (i32 (/ (f64 1.0) (f64 0.0))))
+      (= n 11) (print (u8 (/ (f32 -1.0) (f32 0.0))))
+      (= n 12) (print (i32 (/ (f32 0.0) (f32 0.0))))
 
       :else (println "?"))
     0))
diff --git a/test/programs/macro-gensym-rounds.flan b/test/programs/macro-gensym-rounds.flan
new file mode 100644
index 00000000..74584556
--- /dev/null
+++ b/test/programs/macro-gensym-rounds.flan
@@ -0,0 +1,24 @@
+;;;; Two gensyms from two macro modules are never the same name.
+;;;;
+;;;; `outer` calls `baked` in its body, so `baked` is compiled in a round of
+;;;; its own and `outer`'s body is expanded against that module before `outer`
+;;;; is compiled. The gensym `baked` draws there becomes a literal in
+;;;; `outer`'s code; the one `outer` draws itself comes from the later module
+;;;; the program is expanded with. `main` comes first so that its expansion is
+;;;; that module's first draw. Were the two the same name, the second binding
+;;;; would shadow the first and this would print 200.
+
+(defn main [] i32
+  (println (outer 1))
+  0)
+
+;; Expands to code that builds the symbol this expansion drew.
+(defmacro baked []
+  (match (gensym)
+    (Form.Sym s) `(Form.Sym {.s ~(Form.Str {.s s})})
+    _ `(form-nil)))
+
+(defmacro outer [a]
+  (let [g (baked)
+        h (gensym)]
+    `(let [~g ~a  ~h 100] (+ ~g ~h))))
diff --git a/test/programs/recur.flan b/test/programs/recur.flan
index 5c6f32a0..e03cf332 100644
--- a/test/programs/recur.flan
+++ b/test/programs/recur.flan
@@ -99,4 +99,10 @@
              (Some v) (recur (+ i 1) (+ acc v))
              None     acc)))
   (println "")                                  ; 0+1+2+3 = 6
+
+  ;; The bindings are sequential, as a let's are: the second initialiser reads
+  ;; the first name. Only the initial values are; recur still rebinds at once.
+  (print (loop [a 1  b (+ a 10)]
+           (if (> a 3) b (recur (+ a 1) (+ b a)))))
+  (println "")                                  ; 11+1+2+3 = 17
   0)
diff --git a/test/programs/u64-decimal.flan b/test/programs/u64-decimal.flan
new file mode 100644
index 00000000..00b0c92a
--- /dev/null
+++ b/test/programs/u64-decimal.flan
@@ -0,0 +1,16 @@
+;;;; A u64 constant above 2^63 written in decimal, and an integer literal too
+;;;; wide for i32 as a cast's argument.
+
+(defconst top u64 18446744073709551615)
+(defonce fnv u64 14695981039346656037)
+
+(defn main [] i32
+  (println top)
+  (println fnv)
+  (println (u64 2935910691))
+  (println (u64 18446744073709551615))
+  (println (i64 -5000000000))
+  (println (f64 4000000000))
+  ;; A literal that fits i32 keeps its default and is cast, as before.
+  (println (u32 -1))
+  0)
diff --git a/test/programs/vec-new-shadow.flan b/test/programs/vec-new-shadow.flan
new file mode 100644
index 00000000..9be6e154
--- /dev/null
+++ b/test/programs/vec-new-shadow.flan
@@ -0,0 +1,14 @@
+;;;; A program's own vec-new is an ordinary function: a bracket passed to it
+;;;; is an array value, not an element type. builtin/vec-new is still the
+;;;; builtin and still reads one as a type.
+
+(defn vec-new [xs [1 i32]] i32 (at xs 0))
+
+(defn main [] i32
+  (let [x 7
+        v (builtin/vec-new [u8])]
+    (println (vec-new [x]))
+    (push v (bytes-view "ab"))
+    (println (length (at v 0)))
+    (free v))
+  0)
diff --git a/test/programs/vec-new-type.flan b/test/programs/vec-new-type.flan
new file mode 100644
index 00000000..5d338a70
--- /dev/null
+++ b/test/programs/vec-new-type.flan
@@ -0,0 +1,25 @@
+;;;; vec-new and map-new take a type expression where they take a type, so a
+;;;; local can hold a Vec of slices, of arrays or of pointers with nothing
+;;;; else naming the element type. The last Vec names an allocator after its
+;;;; type, which is the one argument that may follow.
+
+(defn main [] i32
+  (let [a     (arena-new 4096)
+        words (vec-new [u8])
+        pairs (vec-new [2 i32])
+        ptrs  (vec-new (Ptr i32))
+        opts  (vec-new (Option i64) a)
+        m     (map-new string [u8])
+        x     (i32 7)]
+    (push words (bytes-view "ab"))
+    (push words (bytes-view "cde"))
+    (push pairs [3 4])
+    (push ptrs (addr x))
+    (push opts (Some (i64 9)))
+    (put m "k" (bytes-view "xyz"))
+    (println (length words) (length (at words 1))
+             (at (at pairs 0) 1) (deref (at ptrs 0))
+             (match (at opts 0) (Some v) v None -1)
+             (match (get m "k") (Some v) (length v) None -1))
+    (free words) (free pairs) (free ptrs) (free m))
+  0)
diff --git a/test/test_acceptance.ml b/test/test_acceptance.ml
index 2e7b708b..f3677f73 100644
--- a/test/test_acceptance.ml
+++ b/test/test_acceptance.ml
@@ -501,7 +501,25 @@ let () =
        rather than running out of stack. The swap line is the other — recur
        rebinds every name at once, and interleaved writes would print 1. *)
     outputs "loop and recur" "programs/recur.flan"
-      "10\n2\n21\n8\n10000000\n64\n012\n0\n4\n012\n6\n";
+      "10\n2\n21\n8\n10000000\n64\n012\n0\n4\n012\n6\n17\n";
+    (* A type expression where vec-new and map-new take a type: a slice, an
+       array, a pointer and an option, with nothing else naming the element. *)
+    outputs "vec-new takes a type expression" "programs/vec-new-type.flan"
+      "2 3 4 7 9 3\n";
+    outputs ~x86:true "vec-new takes a type expression, x86"
+      "programs/vec-new-type.flan" "2 3 4 7 9 3\n";
+    (* A program's own vec-new takes its arguments as values; the builtin,
+       reached as builtin/vec-new, still reads a bracket as a type. *)
+    outputs "a vec-new of the program's own" "programs/vec-new-shadow.flan"
+      "7\n2\n";
+    (* A u64 above 2^63 in decimal, and a cast of a literal too wide for i32. *)
+    let u64_out =
+      "18446744073709551615\n14695981039346656037\n2935910691\n\
+       18446744073709551615\n-5000000000\n4e+09\n4294967295\n"
+    in
+    outputs "a u64 constant in decimal" "programs/u64-decimal.flan" u64_out;
+    outputs ~x86:true "a u64 constant in decimal, x86"
+      "programs/u64-decimal.flan" u64_out;
     (* into. The count of pulls is the assertion a unit test cannot make: one
        pass, one call per element per stage it reaches, and no intermediate
        collection anywhere. The two show lines either side of it are the same
@@ -2543,8 +2561,8 @@ let () =
        no overflow case because it has no most-negative value, and a float
        division by zero, which is an infinity and is a defined answer this
        language has no business refusing. *)
-    let arith ?opt () =
-      let exe = compile ?opt "programs/arith.flan" in
+    let arith ?opt ?x86 () =
+      let exe = compile ?opt ?x86 "programs/arith.flan" in
       let traps name arg reason =
         let code, text = run exe (Some arg) in
         if code <> 134
@@ -2587,7 +2605,7 @@ let () =
          would have waved it through into an fptosi that is as undefined for a
          NaN as it is for 1e300. *)
       traps "NaN cast to an integer" "7"
-        "does not fit the integer type it is cast to";
+        "this value is NaN, which has no integer value to cast to";
       (* One width down, and this is the case the two backends disagreed about
          *silently* rather than both dying: x86 loaded the operands
          sign-extended into 64-bit registers, divided there and truncated on
@@ -2604,10 +2622,21 @@ let () =
          and this is the row that says so rather than the comment. *)
       traps "an f32 too large for an i32" "9"
         "which holds [-2147483648 2147483647]";
+      (* NaN and the infinities are named: they did not overshoot a range,
+         they have no integer value at all. *)
+      traps "an infinity cast to an integer" "10"
+        "this value is infinite, which has no integer value to cast to";
+      traps "an f32 negative infinity cast to a u8" "11"
+        "this value is infinite, which has no integer value to cast to";
+      traps "an f32 NaN cast to an integer" "12"
+        "this value is NaN, which has no integer value to cast to";
       (try Sys.remove exe with Sys_error _ -> ())
     in
     arith ();
     arith ~opt:"-O0" ();
+    (* The x86 backend picks the code with its own instructions, so the three
+       named cases are asserted there as well as in the survey. *)
+    arith ~x86:true ();
 
     (* The release build drops the guards. Asserted on the IR and not by
        running an unchecked program, for the reason the bounds case gives: an
@@ -2646,7 +2675,7 @@ let () =
        op 2\nlhs -9223372036854775808\nrhs -1\nop 3\n\
        cast 3\ncast -3\n\
        op 4\nlhs -9223372036854775808\nrhs 9223372036854775807\nop 4\n\
-       cast8 12\nlhs -128\nrhs 127\nop 4\n\
+       cast8 12\nlhs -128\nrhs 127\nop 5\n\
        lit 4611686018427387903\nu 14\n\
        frames 4\nskipped 8\ncleaned 12\n"
     in
@@ -3896,6 +3925,11 @@ level "1"
     outputs ~dev:true "a macro's parameter list, dev"
       "programs/macro-params.flan" macro_params_out;
 
+    (* A gensym drawn in one round's module and one drawn in the module the
+       program is expanded with are different names. 200 is the two colliding. *)
+    outputs "gensym counts across macro modules"
+      "programs/macro-gensym-rounds.flan" "101\n";
+
     (* A macro declared in an imported *package*, which is the half the
        refusal at [a package's macro is not visible unqualified] above leaves
        out. The program calls six of them qualified and one of its own
diff --git a/test/test_flan.ml b/test/test_flan.ml
index 3c606aef..d39a06df 100644
--- a/test/test_flan.ml
+++ b/test/test_flan.ml
@@ -92,6 +92,14 @@ let () =
   reads "bare plus"      "+" "+";
   reads "float"          "0.05" "0.05";
   reads "hex"            "0xE6B800FF" "3870818559";
+  (* A decimal between 2^63 and 2^64 is its bit pattern, as hex is; one past
+     2^64, or a negative one past the smallest i64, is still malformed. *)
+  reads "u64 decimal"    "18446744073709551615" "18446744073709551615";
+  reads "hex top bit"    "0xFFFFFFFFFFFFFFFF" "0xFFFFFFFFFFFFFFFF";
+  rejects "decimal past 2^64" "18446744073709551616"
+    ~needle:"malformed integer literal";
+  rejects "negative decimal past i64" "-9223372036854775809"
+    ~needle:"malformed integer literal";
   reads "string"         "\"SAND\"" "\"SAND\"";
   reads "symbol"         "empty-at?" "empty-at?";
   reads "qualified"      "rl/draw-fps" "rl/draw-fps";
@@ -6042,6 +6050,58 @@ let () =
   rejects_check "vec-new with no element type and nothing to take one from"
     ~needle:"nothing here says what (vec-new) is a Vec of"
     "(defn f [x $t] i32 (do x (let [v (vec-new)] (free v) 0)))";
+  (* A type expression in a type position, generic or not. *)
+  accepts "vec-new over a slice of a type variable"
+    "(defn f [x [$t]] i32 (let [v (vec-new [$t])] (push v x) \
+       (let [n (length v)] (free v) n)))";
+  rejects_check "map-new with a key type expression and no value type"
+    ~needle:"(map-new) names a key and no value"
+    "(defn f [] i32 (let [m (map-new [u8])] (free m) 0))";
+  accepts "vec-new over a function type returning unit"
+    "(defn f [] i32 (let [v (vec-new (Fn [i32] ()))] (free v) 0))";
+  accepts "a program's own vec-new takes an array literal"
+    "(defn vec-new [xs [3 i32]] i32 (at xs 2)) \
+     (defn f [] i32 (vec-new [1 2 3]))";
+  accepts "builtin/vec-new over a type expression"
+    "(defn f [] i32 (let [v (builtin/vec-new [u8])] (free v) 0))";
+
+  (* An integer written at or above 2^63 — decimal, or hex with the top bit
+     set — is a u64 and nothing else, and a refusal prints it as written. *)
+  accepts "a wide decimal at u64"
+    "(defconst a u64 18446744073709551615) (defonce b u64 0xFFFFFFFFFFFFFFFF) \
+     (defn f [x u64] u64 (+ x 9223372036854775808)) \
+     (defn g [] f64 (f64 (u64 12345678901234567890)))";
+  accepts "a negative decimal is still a u64 bit pattern"
+    "(defconst a u64 -1)";
+  rejects_check "a wide decimal with nothing to say u64"
+    ~needle:"18446744073709551615 does not fit in i32, the type an integer \
+             literal takes when nothing says otherwise — write (u64 \
+             18446744073709551615)"
+    "(defn f [] () (println 18446744073709551615))";
+  rejects_check "a wide decimal cast to i64"
+    ~needle:"18446744073709551615 does not fit in i64"
+    "(defn f [] i64 (i64 18446744073709551615))";
+  rejects_check "a wide decimal cast to f64"
+    ~needle:"write (f64 (u64 18446744073709551615))"
+    "(defn f [] f64 (f64 18446744073709551615))";
+  rejects_check "a wide decimal constant at i32"
+    ~needle:"18446744073709551615 does not fit in i32"
+    "(defconst x i32 18446744073709551615)";
+  rejects_check "a wide decimal constant at f64"
+    ~needle:"write (f64 (u64 12345678901234567890))"
+    "(defconst x f64 12345678901234567890)";
+  rejects_check "a wide decimal argument to an i8 parameter"
+    ~needle:"18446744073709551600 does not fit in i8"
+    "(defn g [a i8] i8 a) (defn f [] i8 (g 18446744073709551600))";
+  rejects_check "a wide decimal operand prints as written"
+    ~needle:"9223372036854775808 does not fit in i32"
+    "(defn f [] () (println (+ 1 9223372036854775808)))";
+  rejects_check "a hex literal with the top bit set at i32"
+    ~needle:"0xFFFFFFFFFFFFFFFF does not fit in i32"
+    "(defconst x i32 0xFFFFFFFFFFFFFFFF)";
+  rejects_check "a hex literal with the top bit set at i64"
+    ~needle:"0xFFFFFFFFFFFFFFFF does not fit in i64"
+    "(defconst x i64 0xFFFFFFFFFFFFFFFF)";
   (* And a sigil on a name nothing binds is answered as the unbound variable
      it is, rather than as a missing element type — with the names that *are*
      bound, because inside a signature that introduces one the mistake is