spec: gensym + symbol interning (OCaml + tests)

gensym_counter ref + gensym/string->symbol/symbol->string/intern/symbol-interned?
primitives in sx_primitives.ml. Fix ListRef case in seq_to_list on both
sx_ref.ml and sx_primitives.ml. 19 new tests in test-gensym.sx.
OCaml 4450/1080, JS 2205/2497, zero regressions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

spec/tests/test-gensym.sx

@@ -0,0 +1,78 @@
+(defsuite
+  "gensym"
+  (deftest "gensym returns a symbol" (assert= true (symbol? (gensym))))
+  (deftest
+    "gensym default prefix is g"
+    (let
+      ((s (symbol-name (gensym))))
+      (assert= true (string-contains? s "g"))))
+  (deftest
+    "gensym with prefix uses that prefix"
+    (let
+      ((s (symbol-name (gensym "var"))))
+      (assert= "var" (substring s 0 3))))
+  (deftest
+    "gensym produces unique symbols"
+    (let
+      ((a (gensym)) (b (gensym)))
+      (assert= false (= (symbol-name a) (symbol-name b)))))
+  (deftest
+    "gensym same prefix produces unique symbols"
+    (let
+      ((a (gensym "x")) (b (gensym "x")) (c (gensym "x")))
+      (assert= false (= (symbol-name a) (symbol-name b)))
+      (assert= false (= (symbol-name b) (symbol-name c)))))
+  (deftest
+    "gensym counter increases: names differ"
+    (let
+      ((a (gensym "k")) (b (gensym "k")))
+      (assert= false (= (symbol-name a) (symbol-name b)))))
+  (deftest
+    "gensym no-arg and prefix-arg both unique"
+    (let
+      ((a (gensym)) (b (gensym "g")))
+      (assert= false (= (symbol-name a) (symbol-name b)))))
+  (deftest
+    "string->symbol returns a symbol"
+    (assert= true (symbol? (string->symbol "hello"))))
+  (deftest
+    "string->symbol symbol has correct name"
+    (assert= "hello" (symbol-name (string->symbol "hello"))))
+  (deftest
+    "string->symbol empty string"
+    (assert= true (symbol? (string->symbol ""))))
+  (deftest
+    "symbol->string returns a string"
+    (assert= true (string? (symbol->string (quote foo)))))
+  (deftest
+    "symbol->string round-trips with string->symbol"
+    (assert= "hello" (symbol->string (string->symbol "hello"))))
+  (deftest
+    "string->symbol/symbol->string round-trip"
+    (let
+      ((sym (string->symbol "my-var")))
+      (assert= "my-var" (symbol->string sym))))
+  (deftest
+    "intern returns a symbol"
+    (assert= true (symbol? (intern "foo"))))
+  (deftest
+    "intern same as string->symbol"
+    (assert= "bar" (symbol-name (intern "bar"))))
+  (deftest
+    "symbol-interned? true for literal symbols"
+    (assert= true (symbol-interned? (quote hello))))
+  (deftest
+    "symbol-interned? true for gensym'd symbol"
+    (assert= true (symbol-interned? (gensym "g"))))
+  (deftest
+    "symbol-interned? true for string->symbol"
+    (assert= true (symbol-interned? (string->symbol "test"))))
+  (deftest
+    "multiple gensym calls all unique"
+    (let
+      ((syms (map (fn (i) (gensym "t")) (in-range 5))))
+      (let
+        ((names (map symbol-name syms)))
+        (let
+          ((unique-names (reduce (fn (acc n) (if (some (fn (x) (= x n)) acc) acc (cons n acc))) (list) names)))
+          (assert-equal 5 (len unique-names)))))))