sx: step 6 — JS AdtValue + define-type + match

Mirror of OCaml Step 5 to the JavaScript host. Native ADT representation
for define-type instances, with the same dict-shaped shim approach so
spec-level match-pattern code in evaluator.sx works without changes.

- platform.py typeOf: recognize ._adtv tag, return ._type (so
  (type-of (Just 42)) returns "Maybe" not "dict").
- platform.py adds makeAdtValue/isAdtValue helpers and registers
  PRIMITIVES["adt?"], "make-adt-value", "adt-value?".
- platform.py inspect: format AdtValue as "(Ctor f1 f2 ...)" and
  register as a primitive (was missing entirely on JS).
- fixups_js: hand-written define-type override that constructs
  AdtValue via makeAdtValue, with arity check, type/ctor predicates,
  and field accessors. Re-registered via registerSpecialForm so the
  CEK dispatch routes through it.
- dict? unchanged: AdtValue still passes (no _adtv exclusion) so
  the existing (and (dict? v) (get v :_adt) ...) checks in spec
  predicates keep working.

Tests: 2578 pass (was 2575), zero regressions. All 43 ADT tests
pass on the JS host (was 40, the 3 new Step 5 tests for type-of /
adt? / inspect are now green).

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

hosts/javascript/platform.py

@@ -1129,6 +1129,7 @@ PRIMITIVES_JS_MODULES: dict[str, str] = {
   PRIMITIVES["boolean?"] = function(x) { return x === true || x === false; };
   PRIMITIVES["symbol?"] = function(x) { return x != null && x._sym === true; };
   PRIMITIVES["keyword?"] = function(x) { return x != null && x._kw === true; };
+  PRIMITIVES["adt?"] = function(x) { return x !== null && typeof x === "object" && x._adtv === true; };
   PRIMITIVES["component-affinity"] = componentAffinity;
 ''',
 
@@ -1933,12 +1934,30 @@ PLATFORM_JS_PRE = '''
     if (x._regexp) return "regexp";
     if (x._bytevector) return "bytevector";
     if (x._rational) return "rational";
+    if (x._adtv) return x._type;
     if (typeof Node !== "undefined" && x instanceof Node) return "dom-node";
     if (Array.isArray(x)) return "list";
     if (typeof x === "object") return "dict";
     return "unknown";
   }
 
+  // AdtValue — native algebraic data type instance (Step 6 mirror of OCaml Step 5).
+  // Constructed by define-type. Carries _adt:true plus _adtv:true tag so type-of
+  // returns the type name rather than "dict". dict? remains true (shim approach)
+  // so spec-level match-pattern in evaluator.sx works without changes.
+  function makeAdtValue(typeName, ctorName, fields) {
+    return {
+      _adtv: true,
+      _adt: true,
+      _type: typeName,
+      _ctor: ctorName,
+      _fields: fields
+    };
+  }
+  function isAdtValue(x) {
+    return x !== null && typeof x === "object" && x._adtv === true;
+  }
+
   function symbolName(s) { return s.name; }
   function keywordName(k) { return k.name; }
   function makeSymbol(n) { return new Symbol(n); }
@@ -2126,7 +2145,16 @@ PLATFORM_JS_PRE = '''
   }
 
   function error(msg) { throw new Error(msg); }
-  function inspect(x) { return JSON.stringify(x); }
+  function inspect(x) {
+    if (x !== null && typeof x === "object" && x._adtv === true) {
+      var fs = x._fields || [];
+      if (fs.length === 0) return "(" + x._ctor + ")";
+      var parts = [];
+      for (var i = 0; i < fs.length; i++) parts.push(inspect(fs[i]));
+      return "(" + x._ctor + " " + parts.join(" ") + ")";
+    }
+    return JSON.stringify(x);
+  }
   function debugLog() { console.error.apply(console, ["[sx-debug]"].concat(Array.prototype.slice.call(arguments))); }
 
 '''
@@ -2450,6 +2478,7 @@ CEK_FIXUPS_JS = '''
   // Platform functions — defined in platform_js.py, not in .sx spec files.
   // Spec defines self-register via js-emit-define; these are the platform interface.
   PRIMITIVES["type-of"] = typeOf;
+  PRIMITIVES["inspect"] = inspect;
   PRIMITIVES["symbol-name"] = symbolName;
   PRIMITIVES["keyword-name"] = keywordName;
   PRIMITIVES["callable?"] = isCallable;
@@ -4103,7 +4132,56 @@ def fixups_js(has_html, has_sx, has_dom, has_signals=False, has_deps=False, has_
   function clearStores() { _storeRegistry = {}; return NIL; }
   PRIMITIVES["def-store"] = defStore;
   PRIMITIVES["use-store"] = useStore;
-  PRIMITIVES["clear-stores"] = clearStores;''']
+  PRIMITIVES["clear-stores"] = clearStores;
+
+  // -----------------------------------------------------------------------
+  // define-type override — produces native AdtValue instances (Step 6).
+  // The transpiled sfDefineType from evaluator.sx creates plain dict
+  // instances. We override here to construct AdtValue via makeAdtValue so
+  // type-of returns the type name and adt? can distinguish from dicts.
+  // dict? still returns true for AdtValue (shim) so spec-level match-pattern
+  // continues to work without changes.
+  // -----------------------------------------------------------------------
+  var _sfDefineTypeAdt = function(args, env) {
+    var typeSym = first(args);
+    var ctorSpecs = rest(args);
+    var typeName = symbolName(typeSym);
+    var ctorNames = map(function(spec) { return symbolName(first(spec)); }, ctorSpecs);
+    if (!isSxTruthy(envHas(env, "*adt-registry*"))) {
+      envBind(env, "*adt-registry*", {});
+    }
+    envGet(env, "*adt-registry*")[typeName] = ctorNames;
+    envBind(env, typeName + "?", function(v) { return isAdtValue(v) && v._type === typeName; });
+    for (var _i = 0; _i < ctorSpecs.length; _i++) {
+      (function(spec) {
+        var cn = symbolName(first(spec));
+        var fieldNames = map(function(f) { return symbolName(f); }, rest(spec));
+        var arity = fieldNames.length;
+        envBind(env, cn, function() {
+          var ctorArgs = Array.prototype.slice.call(arguments, 0);
+          if (ctorArgs.length !== arity) {
+            throw new Error(cn + ": expected " + arity + " args, got " + ctorArgs.length);
+          }
+          return makeAdtValue(typeName, cn, ctorArgs);
+        });
+        envBind(env, cn + "?", function(v) { return isAdtValue(v) && v._ctor === cn; });
+        for (var _j = 0; _j < fieldNames.length; _j++) {
+          (function(idx, fieldName) {
+            envBind(env, cn + "-" + fieldName, function(v) {
+              if (!isAdtValue(v)) throw new Error(cn + "-" + fieldName + ": not an ADT");
+              if (idx >= v._fields.length) throw new Error(cn + "-" + fieldName + ": index out of bounds");
+              return v._fields[idx];
+            });
+          })(_j, fieldNames[_j]);
+        }
+      })(ctorSpecs[_i]);
+    }
+    return NIL;
+  };
+  PRIMITIVES["sf-define-type"] = _sfDefineTypeAdt;
+  registerSpecialForm("define-type", _sfDefineTypeAdt);
+  PRIMITIVES["make-adt-value"] = makeAdtValue;
+  PRIMITIVES["adt-value?"] = isAdtValue;''']
     if has_deps:
         lines.append('''
   // Platform deps functions (native JS, not transpiled — need explicit registration)