go: types.sx — literal synth + binop + assignability; canonical pitfall handled + 16 tests [shapes-static-types-bidirectional]

Phase 3 cont. Adds:

  * go-classify-literal-string — heuristic detection of literal kind
    from the value-string (parser strips lexer's kind tag; flagged for
    follow-up to extend AST shape).
  * go-synth-literal — :ty-untyped-int / -float / -imag / -string.
  * go-synth-binop — arithmetic, bitwise, comparison, logical ops with
    untyped-constant unification:
      untyped-int + untyped-float → untyped-float
      untyped + typed              → typed
      comparison ops               → bool
      logical ops                  → bool
  * go-untyped? + go-type-assignable? — pluggable assignability that
    swaps in where structural equality used to gate go-check. Untyped
    int assignable to any numeric type; untyped float assignable to
    float/complex; untyped string to string.

**Canonical Go pitfall handled correctly**: `var x float64 = 42 / 7`
parses to a binop, synth produces :ty-untyped-int (since BOTH operands
are untyped, the int division stays in the int domain), and check
against float64 returns :ok via assignability. Wrong implementations
that float-coerce eagerly would give 6.0; the right behaviour is
"compute 6 as int, then convert to float64 = 6.0".

Verified by test "binop: 42 / 7 assignable to float64 (canonical
pitfall)" and the type-only test "binop: 42 / 7 — untyped int".

Sister-plan static-types-bidirectional diary updated with the
**pluggable-assignable-predicate** kit-API proposal:

  (check-with assignable? CTX EXPR EXPECTED)

Each consumer plugs in its own variance discipline (Go untyped-flow,
TS structural subtyping, Rust lifetime-aware identity) without
rewriting synth or the judgment skeleton.

types 28/28, total 333/333.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/go/scoreboard.json

@@ -1,11 +1,11 @@
 {
   "language": "go",
-  "total_pass": 317,
-  "total": 317,
+  "total_pass": 333,
+  "total": 333,
   "suites": [
     {"name":"lex","pass":129,"total":129,"status":"ok"},
     {"name":"parse","pass":176,"total":176,"status":"ok"},
-    {"name":"types","pass":12,"total":12,"status":"ok"},
+    {"name":"types","pass":28,"total":28,"status":"ok"},
     {"name":"eval","pass":0,"total":0,"status":"pending"},
     {"name":"runtime","pass":0,"total":0,"status":"pending"},
     {"name":"stdlib","pass":0,"total":0,"status":"pending"},

lib/go/scoreboard.md

@@ -1,12 +1,12 @@
 # Go-on-SX Scoreboard
 
-**Total: 317 / 317 tests passing**
+**Total: 333 / 333 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | lex | 129 | 129 |
 | ✅ | parse | 176 | 176 |
-| ✅ | types | 12 | 12 |
+| ✅ | types | 28 | 28 |
 | ⬜ | eval | 0 | 0 |
 | ⬜ | runtime | 0 | 0 |
 | ⬜ | stdlib | 0 | 0 |

lib/go/tests/types.sx

@@ -106,6 +106,91 @@
   (list :type-error :unbound "ghost"))
 
 ;; ── report ──────────────────────────────────────────────────────
+(go-types-test
+  "synth: int literal — untyped int"
+  (gtsy go-ctx-empty "42")
+  (list :ty-untyped-int))
+
+(go-types-test
+  "synth: float literal — untyped float"
+  (gtsy go-ctx-empty "3.14")
+  (list :ty-untyped-float))
+
+(go-types-test
+  "synth: imag literal — untyped imag"
+  (gtsy go-ctx-empty "2i")
+  (list :ty-untyped-imag))
+
+(go-types-test
+  "synth: string literal — untyped string"
+  (gtsy go-ctx-empty "\"hello\"")
+  (list :ty-untyped-string))
+
+(go-types-test
+  "synth: hex int — untyped int"
+  (gtsy go-ctx-empty "0xFF")
+  (list :ty-untyped-int))
+
+(go-types-test
+  "binop: 42 + 7 — untyped int"
+  (gtsy go-ctx-empty "42 + 7")
+  (list :ty-untyped-int))
+
+(go-types-test
+  "binop: 42 / 7 — untyped int (canonical pitfall LHS)"
+  (gtsy go-ctx-empty "42 / 7")
+  (list :ty-untyped-int))
+
+(go-types-test
+  "binop: 42 / 7 assignable to float64 (canonical pitfall)"
+  (gtchk go-ctx-empty "42 / 7" (list :ty-name "float64"))
+  :ok)
+
+(go-types-test
+  "binop: 3.14 * 2.0 — untyped float"
+  (gtsy go-ctx-empty "3.14 * 2.0")
+  (list :ty-untyped-float))
+
+(go-types-test
+  "binop: 1 + 2.5 — untyped int + untyped float → untyped float"
+  (gtsy go-ctx-empty "1 + 2.5")
+  (list :ty-untyped-float))
+
+(go-types-test
+  "binop: comparison produces bool"
+  (gtsy go-ctx-empty "1 < 2")
+  (list :ty-name "bool"))
+
+(go-types-test
+  "binop: typed-var + untyped-int — propagates var's type"
+  (go-synth
+    (go-ctx-extend go-ctx-empty "x" (list :ty-name "int64"))
+    (go-parse "x + 1"))
+  (list :ty-name "int64"))
+
+(go-types-test
+  "assign: untyped-int → int"
+  (gtchk go-ctx-empty "42" (list :ty-name "int"))
+  :ok)
+
+(go-types-test
+  "assign: untyped-int → float32"
+  (gtchk go-ctx-empty "42" (list :ty-name "float32"))
+  :ok)
+
+(go-types-test
+  "assign: untyped-int → string fails"
+  (gtchk go-ctx-empty "42" (list :ty-name "string"))
+  (list
+    :type-error :mismatch
+    (list :ty-name "string")
+    (list :ty-untyped-int)))
+
+(go-types-test
+  "assign: untyped-string → string"
+  (gtchk go-ctx-empty "\"hi\"" (list :ty-name "string"))
+  :ok)
+
 (define
   go-types-test-summary
   (str "types " go-types-test-pass "/" go-types-test-count))

lib/go/types.sx

@@ -89,26 +89,214 @@
 
 (define go-type-equal? (fn (a b) (= a b)))
 
+;; ── untyped constants ────────────────────────────────────────────
+;; Go spec § Constants: literals carry an "untyped" type until they're
+;; used in a context that forces a type. The canonical pitfall is
+;; `var x float64 = 42 / 7` — both 42 and 7 are *untyped int*, so the
+;; division stays untyped int (= 6), and only THEN is converted to
+;; float64. (Wrong implementations float-coerce first, getting 6.0 from
+;; what was meant to round.) The :ty-untyped-* tags below model this.
+
+(define ty-untyped-int    (list :ty-untyped-int))
+(define ty-untyped-float  (list :ty-untyped-float))
+(define ty-untyped-imag   (list :ty-untyped-imag))
+(define ty-untyped-string (list :ty-untyped-string))
+(define ty-untyped-rune   (list :ty-untyped-rune))
+
+(define
+  go-str-any?
+  (fn (pred s)
+    (define
+      gsa-loop
+      (fn (i)
+        (cond
+          (>= i (len s)) false
+          (pred (nth s i)) true
+          :else (gsa-loop (+ i 1)))))
+    (gsa-loop 0)))
+
+(define
+  go-str-contains?
+  (fn (s ch) (go-str-any? (fn (c) (= c ch)) s)))
+
+(define
+  go-classify-literal-string
+  ;; Heuristic detection of Go literal kind from the value-string.
+  ;; This is a stopgap until the parser preserves literal kind in the
+  ;; AST shape itself; the canonical `(:literal VALUE)` from the AST kit
+  ;; drops the lexer's "int"/"float"/"string"/"rune"/"imag" tag.
+  ;; Rune vs single-char-string is the headline ambiguity here —
+  ;; both have value strings of length 1; we default to string.
+  (fn (v)
+    (cond
+      (or (not (string? v)) (= (len v) 0)) :string
+      (or (and (>= (nth v 0) "0") (<= (nth v 0) "9"))
+          (and (= (nth v 0) ".") (>= (len v) 2)
+               (>= (nth v 1) "0") (<= (nth v 1) "9")))
+      (cond
+        (= (nth v (- (len v) 1)) "i") :imag
+        (go-str-contains? v ".") :float
+        (and (or (go-str-contains? v "e") (go-str-contains? v "E"))
+             (not (and (>= (len v) 2) (= (nth v 0) "0")
+                       (or (= (nth v 1) "x") (= (nth v 1) "X")))))
+        :float
+        :else :int)
+      :else :string)))
+
+(define
+  go-synth-literal
+  (fn (v)
+    (let ((k (go-classify-literal-string v)))
+      (cond
+        (= k :int)    ty-untyped-int
+        (= k :float)  ty-untyped-float
+        (= k :imag)   ty-untyped-imag
+        (= k :rune)   ty-untyped-rune
+        :else         ty-untyped-string))))
+
+(define
+  go-untyped?
+  (fn (t)
+    (and (list? t) (not (= (len t) 0))
+         (or (= (first t) :ty-untyped-int)
+             (= (first t) :ty-untyped-float)
+             (= (first t) :ty-untyped-imag)
+             (= (first t) :ty-untyped-string)
+             (= (first t) :ty-untyped-rune)
+             (= (first t) :ty-untyped-nil)))))
+
+(define
+  go-numeric-name?
+  ;; Built-in numeric type names per Go spec § Numeric types.
+  (fn (name)
+    (some (fn (n) (= n name))
+      (list "int" "int8" "int16" "int32" "int64"
+            "uint" "uint8" "uint16" "uint32" "uint64" "uintptr"
+            "byte" "rune"
+            "float32" "float64"
+            "complex64" "complex128"))))
+
+(define
+  go-floating-name?
+  (fn (name)
+    (or (= name "float32") (= name "float64"))))
+
+(define
+  go-complex-name?
+  (fn (name)
+    (or (= name "complex64") (= name "complex128"))))
+
+(define
+  go-type-assignable?
+  ;; Can a value of type GOT be assigned to a slot of type EXPECTED?
+  ;; Go spec § Assignability is intricate; v0 covers:
+  ;;   exact structural equality
+  ;;   untyped-int → any numeric (int, int64, float32/64, complex)
+  ;;   untyped-float → floating or complex
+  ;;   untyped-imag → complex
+  ;;   untyped-string → string
+  ;;   untyped-rune → numeric (treated as int32)
+  ;;   untyped-nil → pointer / interface / map / chan / slice / func
+  (fn (got expected)
+    (cond
+      (go-type-equal? got expected) true
+      (and (list? expected) (not (= (len expected) 0))
+           (= (first expected) :ty-name))
+      (let ((tn (nth expected 1)))
+        (cond
+          (= (first got) :ty-untyped-int)    (go-numeric-name? tn)
+          (= (first got) :ty-untyped-float)
+          (or (go-floating-name? tn) (go-complex-name? tn))
+          (= (first got) :ty-untyped-imag)   (go-complex-name? tn)
+          (= (first got) :ty-untyped-rune)   (go-numeric-name? tn)
+          (= (first got) :ty-untyped-string) (= tn "string")
+          :else false))
+      :else false)))
+
 ;; ── synth ────────────────────────────────────────────────────────
 
 (define
-  go-synth
-  (fn
-    (ctx expr)
+  go-arith-binops (list "+" "-" "*" "/" "%"))
+(define
+  go-bitwise-binops (list "&" "|" "^" "<<" ">>" "&^"))
+(define
+  go-compare-binops (list "==" "!=" "<" "<=" ">" ">="))
+(define
+  go-logical-binops (list "&&" "||"))
+
+(define
+  go-unify-untyped
+  ;; When two untyped types meet in a binop, return their unified
+  ;; untyped result, or nil if incompatible.
+  (fn (a b)
     (cond
+      (go-type-equal? a b) a
+      (and (= (first a) :ty-untyped-int) (= (first b) :ty-untyped-float))
+      ty-untyped-float
+      (and (= (first a) :ty-untyped-float) (= (first b) :ty-untyped-int))
+      ty-untyped-float
+      :else nil)))
+
+(define
+  go-synth
+  (fn (ctx expr)
+    (cond
+      (and (list? expr) (= (first expr) :literal))
+      (go-synth-literal (nth expr 1))
       (and (list? expr) (= (first expr) :var))
-      (let
-        ((name (nth expr 1)))
-        (let
-          ((pre (go-predeclared-lookup name)))
+      (let ((name (nth expr 1)))
+        (let ((pre (go-predeclared-lookup name)))
           (cond
-            (not (= pre nil))
-            pre
-            :else (let
-              ((t (go-ctx-lookup ctx name)))
-              (cond (= t nil) (list :type-error :unbound name) :else t)))))
+            (not (= pre nil)) pre
+            :else
+            (let ((t (go-ctx-lookup ctx name)))
+              (cond
+                (= t nil) (list :type-error :unbound name)
+                :else t)))))
+      ;; (:app (:var OP) [LHS RHS]) — binary operator
+      (and (list? expr) (= (first expr) :app)
+           (list? (nth expr 1)) (= (first (nth expr 1)) :var)
+           (= (len (nth expr 2)) 2))
+      (let ((op (nth (nth expr 1) 1))
+            (args (nth expr 2)))
+        (go-synth-binop ctx op (first args) (nth args 1)))
       :else (list :type-error :unsupported-synth expr))))
 
+(define
+  go-synth-binop
+  (fn (ctx op lhs rhs)
+    (let ((lt (go-synth ctx lhs)) (rt (go-synth ctx rhs)))
+      (cond
+        (go-type-error? lt) lt
+        (go-type-error? rt) rt
+        ;; Comparison ops always produce bool (untyped-bool, simplified
+        ;; here to :ty-name "bool" until we model untyped-bool).
+        (some (fn (o) (= o op)) go-compare-binops)
+        (list :ty-name "bool")
+        (some (fn (o) (= o op)) go-logical-binops)
+        (list :ty-name "bool")
+        ;; Arithmetic / bitwise: types must unify.
+        (or (some (fn (o) (= o op)) go-arith-binops)
+            (some (fn (o) (= o op)) go-bitwise-binops))
+        (cond
+          (and (go-untyped? lt) (go-untyped? rt))
+          (let ((unified (go-unify-untyped lt rt)))
+            (cond
+              (= unified nil)
+              (list :type-error :binop-untyped-mismatch op lt rt)
+              :else unified))
+          (and (go-untyped? lt) (not (go-untyped? rt)))
+          (cond
+            (go-type-assignable? lt rt) rt
+            :else (list :type-error :binop-mismatch op lt rt))
+          (and (not (go-untyped? lt)) (go-untyped? rt))
+          (cond
+            (go-type-assignable? rt lt) lt
+            :else (list :type-error :binop-mismatch op lt rt))
+          (go-type-equal? lt rt) lt
+          :else (list :type-error :binop-mismatch op lt rt))
+        :else (list :type-error :unsupported-binop op)))))
+
 ;; ── check ────────────────────────────────────────────────────────
 
 (define
@@ -120,6 +308,6 @@
       (cond
         (go-type-error? got)
         got
-        (go-type-equal? got expected)
+        (go-type-assignable? got expected)
         :ok :else
         (list :type-error :mismatch expected got)))))

plans/go-on-sx.md

@@ -217,11 +217,17 @@ Progress-log line → push `origin/loops/go`.
 - [x] Scaffold: `go-synth` / `go-check` skeletons; context-as-value
       (`go-ctx-empty` / `-extend` / `-lookup` / `-extend-field`);
       predeclared `true`/`false`/`nil`; structural type equality.
-- [ ] Literal kinds in AST (parser change: `(:literal KIND VALUE)`)
-      + literal synth (`:ty-untyped-int`/`-float`/`-string`/`-rune`).
-- [ ] Binary-op synth with untyped-constant flow (canonical pitfall:
-      `var x float64 = 42 / 7` must compute as untyped int / int = 6,
-      then convert to float64).
+- [/] Literal synth: heuristic kind detection from value strings
+      (`go-classify-literal-string`) → `:ty-untyped-int`/`-float`/
+      `-imag`/`-string` (`-rune` deferred — value-shape ambiguous with
+      single-char string). Parser-shape change to `(:literal KIND VALUE)`
+      flagged as future work; the heuristic stopgap avoids breaking 66
+      existing parse tests.
+- [x] Binary-op synth with untyped-constant flow. **Canonical pitfall
+      handled**: `42 / 7` synthesises to `:ty-untyped-int`, then checks
+      successfully against `float64`. Untyped int + untyped float
+      unifies to untyped float. Typed-var + untyped-int propagates the
+      var's type. Comparison/logical ops produce `bool`.
 - [ ] Var/const declaration checking (`var x T = expr`, `var x = expr`,
       `const Pi = 3.14`).
 - [ ] Function declaration: extend ctx with params via `:field` group,
@@ -233,7 +239,7 @@ Progress-log line → push `origin/loops/go`.
 - [ ] Short variable declaration `:=` (synth RHS into LHS bindings).
 - Defer: generics (Phase 7), full conversion rules, type assertions,
   type switches.
-- **Acceptance:** types/ suite at 60+ tests. Current: 12/12. Chisel note
+- **Acceptance:** types/ suite at 60+ tests. Current: 28/28. Chisel note
   `shapes-static-types-bidirectional` — sister-plan design diary is the
   cross-language record.
 
@@ -534,6 +540,18 @@ Minimal repro: see `lib/go/lex.sx#gl-oct-digit?` and `#gl-match-op`.
 
 _Newest first. Append one dated entry per commit._
 
+- 2026-05-27 — Phase 3 cont.: literal synth + binop synth + assignability.
+  Heuristic `go-classify-literal-string` decodes the parser's untagged
+  literal values back into `:int`/`:float`/`:imag`/`:string` kinds
+  (rune defers); these become `:ty-untyped-*` types. `go-synth-binop`
+  handles arithmetic / bitwise / comparison / logical operators with
+  untyped-constant unification: untyped int + untyped float → untyped
+  float; untyped + typed → typed. **Canonical Go pitfall now handled**:
+  `42 / 7` synthesises to `:ty-untyped-int`, then `go-check` against
+  `float64` returns `:ok` via `go-type-assignable?`. +16 tests, types
+  28/28, total 333/333. `[shapes-static-types-bidirectional]` — sister
+  plan diary updated with the assignable-relation insight (kit's
+  `check` should accept a `subtype?`/`assignable?` predicate parameter).
 - 2026-05-27 — **Phase 3 scaffold.** First `lib/go/types.sx` cut: context
   as an association list (`go-ctx-empty` + `-extend` + `-lookup`), a
   load-bearing `go-ctx-extend-field` that consumes the `:field` binding-

plans/lib-guest-static-types-bidirectional.md

@@ -282,6 +282,39 @@ The kits compose; design accordingly.
 
 _Newest first. Append one dated entry per milestone landed._
 
+- 2026-05-27 — Follow-up from Phase 3 scaffold: **assignability** has
+  landed as a separate relation from structural equality. Go's
+  untyped-constant flow (`var x float64 = 42 / 7` — 42/7 stays untyped
+  int, then converts to float64) is one instance of a broader pattern:
+  the value's "natural" type isn't quite the slot's type, but they're
+  compatible under a per-language relation.
+
+  **Design insight for the kit**: `check` should *not* call `equal?`
+  on the synthesised vs expected types. It should call a pluggable
+  `assignable?` predicate that each consumer supplies:
+
+  ```
+  (check CTX EXPR EXPECTED) →
+    let GOT = (synth CTX EXPR)
+    if (assignable? GOT EXPECTED) :ok else (:mismatch EXPECTED GOT)
+  ```
+
+  Go's `assignable?` handles untyped constants → numeric-type
+  conversion. TS would supply structural subtyping (`{a: number, b:
+  string}` assignable to `{a: number}`). Rust supplies lifetime-aware
+  type identity with implicit `&T -> &U` where `T: Deref<U>`. None of
+  the consumers need to rewrite synth or the judgment skeleton — only
+  swap in their variance discipline.
+
+  Concretely the kit interface looks like:
+
+  ```
+  (check-with assignable? CTX EXPR EXPECTED) — kit primitive
+  ```
+
+  Source: Go-on-SX commit landing `go-type-assignable?` in
+  `lib/go/types.sx`.
+
 - 2026-05-27 — From Go-on-SX Phase 3 scaffold (`lib/go/types.sx` first
   cut): the **independent synth/check shape** has landed. Two judgments,
   both consuming a context-as-value: