js-on-sx: Function global stub (constructor throws, prototype has stubs)

Several tests check 'new Function("return 1")' — we can't actually
implement that (would need runtime JS eval). Now Function is a dict with
__callable__ that throws TypeError, and a prototype containing call/apply/
bind/toString/length/name stubs so code that probes Function.prototype
doesn't crash with 'Undefined symbol: Function'.

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

lib/js/runtime.sx

@@ -23,12 +23,17 @@
 
 ;; ── Boolean coercion (ToBoolean) ──────────────────────────────────
 
+(define js-function-global {:__callable__ (fn (&rest args) (error "TypeError: Function constructor not supported")) :prototype {:call (fn (&rest args) :js-undefined) :length 0 :bind (fn (&rest args) (fn () :js-undefined)) :toString (fn () "function () { [native code] }") :apply (fn (&rest args) :js-undefined) :name ""}})
+
+;; ── Numeric coercion (ToNumber) ───────────────────────────────────
+
 (define
   js-global-eval
   (fn (&rest args) (if (empty? args) :js-undefined (nth args 0))))
 
-;; ── Numeric coercion (ToNumber) ───────────────────────────────────
+;; Parse a JS-style string to a number. For the slice we just delegate
-
+;; to SX's number parser via `str->num`/`parse-number`. Empty string → 0
+;; per JS (technically ToNumber("") === 0).
 (define
   js-max-value-loop
   (fn
@@ -43,18 +48,15 @@
           cur
           (js-max-value-loop next (- steps 1)))))))
 
-;; Parse a JS-style string to a number. For the slice we just delegate
-;; to SX's number parser via `str->num`/`parse-number`. Empty string → 0
-;; per JS (technically ToNumber("") === 0).
-(define js-undefined :js-undefined)
-
 ;; Safe number-parser. Tries to call an SX primitive that can parse
 ;; strings to numbers; on failure returns 0 (stand-in for NaN so the
 ;; slice doesn't crash).
-(define js-undefined? (fn (v) (= v :js-undefined)))
+(define js-undefined :js-undefined)
 
 ;; Minimal string->number for the slice. Handles integers, negatives,
 ;; and simple decimals. Returns 0 on malformed input.
+(define js-undefined? (fn (v) (= v :js-undefined)))
+
 (define __js_this_cell__ (dict))
 
 (define
@@ -106,6 +108,13 @@
           (js-fn-length (get f "__callable__")))
         (else 0)))))
 
+;; parse a decimal number from a trimmed non-empty string.
+;;   s      — source
+;;   i      — cursor
+;;   acc    — integer part so far (or total for decimals)
+;;   sign   — 1 or -1
+;;   frac?  — are we past the decimal point
+;;   fdiv   — divisor used to scale fraction digits (only if frac?)
 (define
   js-count-real-params
   (fn
@@ -120,13 +129,6 @@
             0
             (+ 1 (js-count-real-params (rest params)))))))))
 
-;; parse a decimal number from a trimmed non-empty string.
-;;   s      — source
-;;   i      — cursor
-;;   acc    — integer part so far (or total for decimals)
-;;   sign   — 1 or -1
-;;   frac?  — are we past the decimal point
-;;   fdiv   — divisor used to scale fraction digits (only if frac?)
 (define
   js-invoke-function-method
   (fn
@@ -177,6 +179,8 @@
         (fn (&rest args) (js-invoke-function-method recv "bind" args)))
       (else :js-undefined))))
 
+;; ── String coercion (ToString) ────────────────────────────────────
+
 (define
   js-invoke-number-method
   (fn
@@ -206,8 +210,6 @@
             (js-to-string key)
             " is not a function (on number)"))))))
 
-;; ── String coercion (ToString) ────────────────────────────────────
-
 (define
   js-invoke-function-objproto
   (fn
@@ -224,6 +226,9 @@
       ((= key "toLocaleString") "function () { [native code] }")
       (else :js-undefined))))
 
+;; ── Arithmetic (JS rules) ─────────────────────────────────────────
+
+;; JS `+`: if either operand is a string → string concat, else numeric.
 (define
   js-invoke-boolean-method
   (fn
@@ -238,9 +243,6 @@
             (js-to-string key)
             " is not a function (on boolean)"))))))
 
-;; ── Arithmetic (JS rules) ─────────────────────────────────────────
-
-;; JS `+`: if either operand is a string → string concat, else numeric.
 (define
   js-num-to-str-radix
   (fn
@@ -352,6 +354,7 @@
             (nth args 5)))
         (else (apply callable args))))))
 
+;; Bitwise + logical-not
 (define
   js-invoke-method
   (fn
@@ -377,7 +380,6 @@
               (error
                 (str "TypeError: " (js-to-string key) " is not a function")))))))))
 
-;; Bitwise + logical-not
 (define
   js-object-builtin-method?
   (fn
@@ -390,6 +392,9 @@
       (= name "valueOf")
       (= name "toLocaleString"))))
 
+;; ── Equality ──────────────────────────────────────────────────────
+
+;; Strict equality (===): no coercion; js-undefined matches js-undefined.
 (define
   js-invoke-object-method
   (fn
@@ -411,16 +416,13 @@
       ((= name "toLocaleString") "[object Object]")
       (else js-undefined))))
 
-;; ── Equality ──────────────────────────────────────────────────────
-
-;; Strict equality (===): no coercion; js-undefined matches js-undefined.
 (define js-upper-case (fn (s) (js-case-loop s 0 "" true)))
 
-(define js-lower-case (fn (s) (js-case-loop s 0 "" false)))
-
 ;; Abstract equality (==): type coercion rules.
 ;; Simplified: number↔string coerce both to number; null == undefined;
 ;; everything else falls back to strict equality.
+(define js-lower-case (fn (s) (js-case-loop s 0 "" false)))
+
 (define
   js-case-loop
   (fn
@@ -436,6 +438,11 @@
               ((cv (cond ((and to-upper? (>= cc 97) (<= cc 122)) (js-code-to-char (- cc 32))) ((and (not to-upper?) (>= cc 65) (<= cc 90)) (js-code-to-char (+ cc 32))) (else c))))
               (js-case-loop s (+ i 1) (str acc cv) to-upper?))))))))
 
+;; ── Relational comparisons ────────────────────────────────────────
+
+;; Abstract relational comparison from ES5.
+;; Numbers compare numerically; two strings compare lexicographically;
+;; mixed types coerce both to numbers.
 (define
   js-code-to-char
   (fn
@@ -495,11 +502,6 @@
       ((= code 122) "z")
       (else ""))))
 
-;; ── Relational comparisons ────────────────────────────────────────
-
-;; Abstract relational comparison from ES5.
-;; Numbers compare numerically; two strings compare lexicographically;
-;; mixed types coerce both to numbers.
 (define
   js-invoke-method-dyn
   (fn (recv key args) (js-invoke-method recv key args)))
@@ -566,6 +568,13 @@
       ((not (= (type-of obj) "dict")) false)
       (else (js-in-walk obj (js-to-string key))))))
 
+;; ── Property access ───────────────────────────────────────────────
+
+;; obj[key] or obj.key in JS. Handles:
+;;   • dicts keyed by string
+;;   • lists indexed by number (incl. .length)
+;;   • strings indexed by number (incl. .length)
+;; Returns js-undefined if the key is absent.
 (define
   js-in-walk
   (fn
@@ -576,13 +585,6 @@
       ((dict-has? obj "__proto__") (js-in-walk (get obj "__proto__") skey))
       (else false))))
 
-;; ── Property access ───────────────────────────────────────────────
-
-;; obj[key] or obj.key in JS. Handles:
-;;   • dicts keyed by string
-;;   • lists indexed by number (incl. .length)
-;;   • strings indexed by number (incl. .length)
-;; Returns js-undefined if the key is absent.
 (define
   Error
   (fn
@@ -619,6 +621,7 @@
           nil)
         this))))
 
+;; Setter — mutates the dict. Returns the new value (JS assignment yields rhs).
 (define
   RangeError
   (fn
@@ -637,7 +640,10 @@
           nil)
         this))))
 
-;; Setter — mutates the dict. Returns the new value (JS assignment yields rhs).
+;; ── Short-circuit logical ops ─────────────────────────────────────
+
+;; `a && b` in JS: if a is truthy return b else return a. The thunk
+;; form defers evaluation of b — the transpiler passes (fn () b).
 (define
   SyntaxError
   (fn
@@ -656,10 +662,6 @@
           nil)
         this))))
 
-;; ── Short-circuit logical ops ─────────────────────────────────────
-
-;; `a && b` in JS: if a is truthy return b else return a. The thunk
-;; form defers evaluation of b — the transpiler passes (fn () b).
 (define
   ReferenceError
   (fn
@@ -678,6 +680,9 @@
           nil)
         this))))
 
+;; ── console.log ───────────────────────────────────────────────────
+
+;; Trivial bridge. `log-info` is available on OCaml; fall back to print.
 (define
   js-function?
   (fn
@@ -690,15 +695,11 @@
         (= t "component")
         (and (= t "dict") (contains? (keys v) "__callable__"))))))
 
-;; ── console.log ───────────────────────────────────────────────────
-
-;; Trivial bridge. `log-info` is available on OCaml; fall back to print.
 (define __js_proto_table__ (dict))
 
-(define __js_next_id__ (dict))
-
 ;; ── Math object ───────────────────────────────────────────────────
 
+(define __js_next_id__ (dict))
 (dict-set! __js_next_id__ "n" 0)
 (define
   js-get-ctor-proto
@@ -768,7 +769,8 @@
       ((= v false) 0)
       ((= (type-of v) "number") v)
       ((= (type-of v) "string") (js-string-to-number v))
-      (else 0))))
+      (else 0))))   ; deterministic placeholder for tests
+
 (define
   js-string-to-number
   (fn
@@ -781,16 +783,16 @@
         ((= trimmed "+Infinity") (js-infinity-value))
         ((= trimmed "-Infinity") (- 0 (js-infinity-value)))
         ((js-is-numeric-string? trimmed) (js-parse-num-safe trimmed))
-        (else (js-nan-value))))))   ; deterministic placeholder for tests
+        (else (js-nan-value))))))
-
-(define
-  js-is-numeric-string?
-  (fn (s) (js-is-numeric-loop s 0 false false false)))
 
 ;; The global object — lookup table for JS names that aren't in the
 ;; SX env. Transpiled idents look up locally first; globals here are a
 ;; fallback, but most slice programs reference `console`, `Math`,
 ;; `undefined` as plain symbols, which we bind as defines above.
+(define
+  js-is-numeric-string?
+  (fn (s) (js-is-numeric-loop s 0 false false false)))
+
 (define
   js-is-numeric-loop
   (fn

lib/js/transpile.sx

@@ -161,6 +161,7 @@
       ((= name "Infinity") (list (js-sym "js-infinity-value")))
       ((= name "eval") (js-sym "js-global-eval"))
       ((= name "globalThis") (js-sym "js-global"))
+      ((= name "Function") (js-sym "js-function-global"))
       (else (js-sym name)))))
 
 ;; ── Unary ops ─────────────────────────────────────────────────────