The batch from two reviews plus the acceptance exit code, item by item

Constraints parsing peeled a body-leading map only when its first key was
literally :where; any other keyword fell through to the body, so a typo'd
key surfaced as a baffling error from inside what was meant as a predicate
and a stray map at body start compiled away silently. Any keyword-first map
is read as a constraint map now, but only when something follows it in the
body — a single-form map body is a real dyn value and not a discarded
statement, so that case is left alone.

An empty map literal still parses as a struct literal, (P {}) still meaning
the zero struct for a real struct name — the parser has no symbol table to
tell (take {}) apart from it at that point. check.ml now catches the case
where the name turns out to be a known function instead and says so, rather
than "unknown struct take".

flan_dyn.c's tag comment still said 6 and 7 were free; keywords and maps
took 4 and a kind field under BOX_OBJ, not new top-level tags, so 5, 6 and 7
are what is actually open for the interop handle. NEXT.md and json.flan both
still pointed at test/programs/arena-edn.flan, gone since edn/read stopped
taking an allocator; both now point at what replaced it.

flan_rt.c's flan_str_eq comment claimed the empty string literal was a
hypothetical null-pointer string; it isn't, its address is an interned
symbol's. The real case the zero-length guard exists for is a zero-length
container converted to a string. check.ml's ordering refusal said a string
has no comparison at all, which stopped being true when typed = and !=
grew strings in daed039 — split the message so an equality refusal and an
ordering refusal say the right noun, and updated the pinned rejects_check
rows to match. string-eq.flan gained the row the fast path most wants
tested, a slice against the prefix it was cut from sharing a base pointer at
different lengths, plus a != row at equal length with differing bytes;
acceptance now carries the real output, captured by running the program on
all three lanes. x86.ml's xor-1 comment now names the 0/1 return contract as
a requirement flan_str_eq must hold, not an incidental fact. SPIKE-DUPLICITY
now says plainly that its equality-and-ordering argument landed in daed039
and marks its transcript as the historical state that argument was made
against. FIX.org ticks M2 queue item 5.

And the acceptance runner: the tail check that turns a nonzero failure count
into exit 1 was already there and already fired — a fresh build with one row
broken already exited 1 before anything here changed. What wasn't proven is
that every path through the file's clang/wasmtime/raylib/lldb probes still
reaches that tail rather than skipping past rows that already failed. An
at_exit guard now closes that class regardless of which path the process
leaves by, flushing stdout first so a failing run's FAIL lines survive
Unix._exit rather than being dropped from the buffer. Verified both
directions with a deliberately broken row: dune test exits nonzero and the
log still carries the FAIL line and the failure count; restored, the same
run is exit 0 with nothing printed but green summaries. The other test
binaries were checked for the same gap and none have it — each gates its
own exit on a single failures ref that the tail already reads.

FIX.org

@@ -424,7 +424,7 @@ rename. typed-flan branch freezes the static language pre-dyn.
 4. nil: arrives with maps. nil <-> None at (Option T) boundaries, trap at
    bare T, (Some nil) unconstructible.
 5. Typed = and != grow strings: bytewise, length + same-pointer fast paths,
-   both backends, one survey program. Ordering stays refused.
+   both backends, one survey program. Ordering stays refused. — LANDED, daed039
 6. defclass = named dyn map + shape tag; CLOS class dispatch AND
    Clojure-style arbitrary dispatch functions. After 1.
 7. dyn if: truthiness (nil/false are false, all else true). Typed stays
@@ -505,11 +505,15 @@ instead of saying something false.
 
 ** Sweep policy, decided 2026-09-19
 A lane runs the fast check and nothing more. `dune test` is the whole of a
-lane's obligation, and it is judged by reading the printed output rather than
-by the exit status, which stays 0 even when the acceptance runner prints
-failures. Running one program directly to capture its real output for an
-acceptance row is still expected; that is cheap. What a lane may no longer do
-is sweep.
+lane's obligation. It used to be judged by reading the printed output rather
+than by trusting the exit status, on the theory that some path through the
+acceptance runner could print a FAIL and still exit 0 — the tail check itself
+already exited 1, but nothing proved every skip path (no clang, no wasmtime,
+no raylib, no lldb) still reached it. test_acceptance.ml now closes that class
+with an `at_exit` handler that holds regardless of which path the process
+leaves by, so the exit status can be trusted again and either check does.
+Running one program directly to capture its real output for an acceptance row
+is still expected; that is cheap. What a lane may no longer do is sweep.
 
 The x86 survey and the sanitizer sweep run once, after several lanes have
 landed, and whatever they turn up is dispatched as fixes in a single batch.

NEXT.md

@@ -1648,7 +1648,9 @@ and the refusals' own words say so: each of them named *teardown* as the problem
 on `can-free` at construction and at every growth — rather than being answered with a hook. This is Odin's position in
 full: `core:encoding/json` ships a hand-written recursive `destroy_value` in the *library* and names parsing against
 `temp_allocator` plus `free_all` as the idiomatic alternative, and neither is a language feature. See spec-memory.md,
-"A container of owning elements lives in a region", and `test/programs/arena-edn.flan`.
+"A container of owning elements lives in a region". `test/programs/arena-edn.flan` was that case's acceptance program;
+it is gone now that `edn/read` answers plain dyn rather than an arena-allocated `(Vec Value)`, and `test/programs/edn-read.flan` is
+where the recursive document is exercised today.
 
 **The safety net, and the better use of effort: a debug tracking allocator.** ASan's leak detection covers memory
 *instrumented* code allocated — the Flan allocator, and it is already wired up and clean. It does **not** cover a leaked

docs/SPIKE-DUPLICITY.md

@@ -105,7 +105,16 @@ that fell out rather than the one that was chosen.
 
 ## 2. Equality and ordering — not two meanings, one side missing a case
 
-Typed `=` is numbers and enums and nothing else. `lib/types.ml:166-168`:
+**Landed in `daed039`** (M2 queue item 5): typed `=` and `!=` now grow the `string` case this section argues
+for, bytewise, with the fast paths `runtime/flan_rt.c`'s `flan_str_eq` carries. `is_equatable` is no longer a
+bare alias for `is_comparable` — `lib/types.ml` now reads `let is_equatable = function String -> true | t ->
+is_comparable t` — and the transcript below, quoted as this section found it, now accepts `(= "hi" "hi")`.
+Ordering was deliberately left alone: `<` and friends still refuse a string, on the same "no collation this
+language has picked" grounds §2 raises, and that half of the verdict did not land. What follows is kept as
+the historical argument that got the equality half moving; read the two paragraphs above as its outcome, not
+as a correction of anything past this point.
+
+Typed `=` is numbers and enums and nothing else, as this was written. `lib/types.ml:166-168` then read:
 
 ```ocaml
 let is_comparable = function Enum _ -> true | t -> is_numeric t
@@ -116,13 +125,13 @@ let is_equatable = is_comparable
 dyn operation that never traps (`SPIKE-DYNAMIC.md:285-287`), and dyn `<` orders text bytewise by `memcmp`
 (`SPIKE-DYNAMIC.md:273-275`).
 
-One probe, both operators, one line apart:
+One probe, both operators, one line apart — as run before `daed039`; the second `println` now accepts too:
 
 ```
 $ flan check b3.flan
 (defn f [x] dyn x)
 (defn main [] i32 (do (println (= (f "hi") (f "hi")))    ; accepted
-                      (println (= "hi" "hi"))            ; refused
+                      (println (= "hi" "hi"))            ; refused, at the time
                       0))
 b3.flan:2:64: = compares machine numbers; string has no built-in comparison (plan.org, Types)
 ```

lib/check.ml

@@ -3056,6 +3056,19 @@ and check_struct ctx ~want loc name kvs =
            "%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)
+       (* [kvs = []] is the parser's one blind spot here: a symbol applied to
+          an empty map literal, [(name {})], parses as a struct literal with
+          no fields regardless of what [name] turns out to be, because the
+          parser has no table to tell a struct name from a function name. If
+          [name] is a known function, the empty map was meant as an argument
+          — and there is no syntax to pass a map literal straight into a call
+          that way, empty or not; every real function argument is a bound
+          name. Naming that is more useful than "unknown struct". *)
+       else if kvs = [] && Hashtbl.mem ctx.env.fns name then
+         fail loc
+           "%s is a function, not a struct — a map literal cannot be passed \
+            directly as an argument; bind it first, as (let [m {}] (%s m))"
+           name name
        else
          Loc.failk "check/unknown-struct" loc ~notes:(declared_note ctx.env name)
            "unknown struct %s" name)
@@ -3989,9 +4002,15 @@ and named_call ctx ~want loc name args =
       ~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);
+      (match name with
+       | "=" | "!=" ->
+         fail loc
+           "%s compares machine numbers, enums and strings; %s has no \
+            built-in equality (plan.org, Types)" name (Types.to_string a.Tast.ty)
+       | _ ->
+         fail loc
+           "%s orders machine numbers; %s has no built-in ordering \
+            (plan.org, Types)" name (Types.to_string a.Tast.ty));
     prim p Types.Bool [ a; b ]
     end
   | "not" ->

lib/parse.ml

@@ -154,11 +154,20 @@ and pitems (items : Form.t list) : Ast.pitem list =
    is what braces mean in the position a body starts in. *)
 let constraints (body : Form.t list) : Ast.pred list * Form.t list =
   match body with
-  (* Only when the first key is [:where] — the one key the map takes. Braces
-     opening on any other keyword are a dyn map literal standing as the body's
-     first form, and belong to the body. *)
-  | ({ Form.v = Form.Map (({ Form.v = Form.Kw "where"; _ } :: _ as kvs)); _ } as m)
-    :: rest ->
+  (* Any map literal whose first key is a keyword is read as a constraint
+     map when something follows it, not just one that opens on [:where]: a
+     keyword-first map is never a struct literal ([is_struct_map] wants a
+     [.field] symbol or [Map []]), and one sitting where the body starts with
+     more body after it is discarded on evaluation — a map literal has no
+     side effects, so that spot is always a mistake and not a case a real
+     program uses. Reading a typo'd key, like [:wheer], as ordinary body code
+     used to print a baffling "unknown function ordered?" from inside what
+     the user meant as a predicate; reading it here instead lets [keys] below
+     say which key it does not recognise. The single-form body, [rest = []],
+     is left alone: there the map is not discarded, it IS the answer — a
+     [(defn f [] dyn {:a 1})] whose whole body is the dyn value to build. *)
+  | ({ Form.v = Form.Map (({ Form.v = Form.Kw _; _ } :: _ as kvs)); _ } as m)
+    :: (_ :: _ as rest) ->
     let pred (p : Form.t) =
       match p.Form.v with
       (* [$t] at a predicate, not bare [t]: the clause talks about the

lib/x86.ml

@@ -2764,7 +2764,14 @@ and prim f (e : Tast.expr) (p : Tast.prim) (args : Tast.expr list) dst =
      [call_native]; only the sense of the answer needs flipping for [!=],
      the same [xor 1] the [Tast.Not] arm below uses on a bool. [check.ml]
      never builds [<] and friends on a string (Types.is_comparable says no),
-     so this arm only ever sees [Eq] or [Ne]. *)
+     so this arm only ever sees [Eq] or [Ne].
+
+     [xor 1] is only correct because [flan_str_eq] is REQUIRED to return
+     exactly 0 or 1 — an int8_t cast from a C [==] expression, not from a
+     truncated wider comparison — and this arm may not be changed to call a
+     function with a looser contract without also widening this to a proper
+     zero-test. The LLVM side (emit.ml) does not share this requirement: its
+     [icmp ne i8 r, 0] tolerates any nonzero byte as true. *)
   | (Tast.Eq | Tast.Ne), [ a; b ] when a.Tast.ty = Types.String ->
     call_native f ~sym:"flan_str_eq" ~args:[ a; b ] ~rty:(Types.Int Types.I8) dst;
     if p = Tast.Ne then begin

runtime/flan_dyn.c

@@ -86,9 +86,10 @@ _Noreturn void flan_trap(const uint8_t *name, int64_t namelen);
  * milliseconds until the year 6429; the box is what keeps the other end of the
  * type honest rather than quietly wrapping. See the doc.
  *
- * Tags 6 and 7 are unspoken for, and that is where a typed handle goes when
- * interop arrives — a (Vec i64) crossing into dyn without being copied. Again,
- * the doc. */
+ * Tags 5, 6 and 7 are unspoken for — keywords and maps took 4 and BOX_OBJ's
+ * [kind] field, not new top-level tags — and that is where a typed handle
+ * goes when interop arrives — a (Vec i64) crossing into dyn without being
+ * copied. Again, the doc. */
 
 typedef uint64_t flan_dyn;
 

runtime/flan_rt.c

@@ -1961,8 +1961,9 @@ int8_t flan_eq_str(const void *a, const void *b, int64_t size, void *xfer) {
  * after the lengths have already been found equal. The zero-length return
  * guards the [memcmp] below: [memcmp(NULL, NULL, 0)] is technically undefined
  * even though every real implementation treats it as a no-op, and a 0-length
- * string built from a null pointer is not a hypothetical here — the empty
- * string literal is one. */
+ * string built from a null pointer is not a hypothetical here — an empty
+ * string literal is not one, its address is an interned symbol's and is never
+ * null, but a zero-length container converted to a string is. */
 int8_t flan_str_eq(const uint8_t *ap, int64_t alen,
                     const uint8_t *bp, int64_t blen) {
   if (alen != blen) return 0;

test/programs/string-eq.flan

@@ -30,6 +30,7 @@
   ;; A one-byte difference at the end, so the length check cannot rule it
   ;; out and the byte loop has to run to the last byte before it can answer.
   (println (= "abd" "abc"))             ; false
+  (println (!= "abd" "abc"))            ; true
 
   ;; Empty strings: the length check's zero case, which the runtime helper
   ;; also uses to skip a memcmp that would otherwise read through a null
@@ -37,4 +38,10 @@
   (println (= "" ""))                   ; true
   (println (= "" "a"))                  ; false
   (println (= "a" ""))                  ; false
+
+  ;; A slice and the prefix it was cut from: same base pointer, different
+  ;; lengths -- the one pair the same-pointer fast path would answer wrong on
+  ;; if it ran before the length check instead of after.
+  (let [s "abcd"]
+    (println (= s (string (slice (bytes s) 0 2)))))  ; false
   0)

test/test_acceptance.ml

@@ -12,6 +12,25 @@ let () = Watchdog.arm ~seconds:1200 "test_acceptance"
 
 let failures = ref 0
 
+(* The tail of this file exits 1 when [failures] is nonzero, but that check
+   is one path among several a run can take: a probe for clang, wasmtime,
+   raylib or lldb can skip a whole section and jump past rows that already
+   failed. Reading through the file to prove every path still reaches the
+   tail check is exactly the kind of proof that quietly stops being true the
+   next time a case is added. An [at_exit] guard makes the invariant hold no
+   matter which path the process leaves by: however this binary exits, if it
+   printed a FAIL it exits nonzero. [Unix._exit] and not [exit] — calling
+   [exit] from inside an [at_exit] handler recurses through [do_at_exit] —
+   but [_exit] skips the channel flush stdlib's own [at_exit] handler does,
+   and handlers run LIFO, so this one would fire first and throw away every
+   row that already printed FAIL, buffered in stdout, before it ever reached
+   the pipe. [flush_all] first is what [watchdog.ml]'s [dying] does for the
+   same reason: a report that eats the rows that failed is worse than the
+   hang it is there to catch. *)
+let () =
+  at_exit (fun () ->
+    if !failures > 0 then begin flush_all (); Unix._exit 1 end)
+
 let scratch = Filename.get_temp_dir_name ()
 
 let run exe arg =
@@ -965,7 +984,7 @@ let () =
        not a row here: a program that ordered two string literals would not
        compile. *)
     let string_eq_out =
-      "true\nfalse\nfalse\ntrue\ntrue\nfalse\nfalse\ntrue\nfalse\nfalse\n"
+      "true\nfalse\nfalse\ntrue\ntrue\nfalse\nfalse\ntrue\ntrue\nfalse\nfalse\nfalse\n"
     in
     outputs "string equality" "programs/string-eq.flan" string_eq_out;
     outputs ~opt:"-O0" "string equality, -O0" "programs/string-eq.flan"

test/test_flan.ml

@@ -1186,17 +1186,17 @@ let () =
   (* ── Unconstrained operators, and everything past milestone 2 ──── *)
   (* M2 queue item 5: typed = and != grow strings, bytewise. Ordering does
      not — there is no collation the language has picked, so < stays
-     refused with the message it already had. *)
+     refused, on the grounds that a string is equatable but not ordered. *)
   accepts "typed = on strings" "(defn f [] bool (= \"a\" \"b\"))";
   accepts "typed != on strings" "(defn f [] bool (!= \"a\" \"b\"))";
   rejects_check "no built-in < on strings"
-    "(defn f [] bool (< \"a\" \"b\"))" ~needle:"no built-in comparison";
+    "(defn f [] bool (< \"a\" \"b\"))" ~needle:"no built-in ordering";
   rejects_check "no built-in <= on strings"
-    "(defn f [] bool (<= \"a\" \"b\"))" ~needle:"no built-in comparison";
+    "(defn f [] bool (<= \"a\" \"b\"))" ~needle:"no built-in ordering";
   rejects_check "no built-in > on strings"
-    "(defn f [] bool (> \"a\" \"b\"))" ~needle:"no built-in comparison";
+    "(defn f [] bool (> \"a\" \"b\"))" ~needle:"no built-in ordering";
   rejects_check "no built-in >= on strings"
-    "(defn f [] bool (>= \"a\" \"b\"))" ~needle:"no built-in comparison";
+    "(defn f [] bool (>= \"a\" \"b\"))" ~needle:"no built-in ordering";
   (* (Vec T) is built. What is still refused is the arity: one element type,
      and a near-miss there would otherwise resolve to a type variable and come
      back as generics. *)

vendor/json/json.flan

@@ -40,10 +40,15 @@
 ;;;; survive the free-all in the cases that had no escapes and not in the
 ;;;; others, which is the kind of contract nobody can hold in their head.
 ;;;;
-;;;; Note what that buys against test/programs/arena-edn.flan, whose header has
-;;;; a section called "One lifetime that is not the region's" for exactly this:
-;;;; its Values point back at `src` and outlive the arena. A Value built out of
-;;;; string-of does not. The source buffer is dead the moment the read returns.
+;;;; Note what that buys against vendor/edn/read.flan's dyn reader, which
+;;;; settled the same question a different way: it takes no allocator at all,
+;;;; because every string it produces is boxed onto the collector's heap on
+;;;; the spot — read-value's "a document owns its strings" rule. This
+;;;; package's split is the one to take when there is a context allocator to
+;;;; put the copy in and a caller who may not want one for every string in the
+;;;; document; the dyn reader's is the one to take when there is no allocator
+;;;; in the picture at all. Either way, a Token's raw `text` is never what
+;;;; outlives the read — only what string-of or the box copies out of it does.
 ;;;;
 ;;;; ── The allocator ───────────────────────────────────────────────────
 ;;;;