haskell: reject untypeable programs — hk-typecheck + hk-run-typed (+9 tests, 464/464)

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

lib/haskell/tests/typecheck.sx

@@ -0,0 +1,44 @@
+;; typecheck.sx — tests for hk-typecheck / hk-run-typed.
+;; Verifies that untypeable programs are rejected and well-typed programs pass.
+
+(define hk-str-has? (fn (s sub) (>= (index-of s sub) 0)))
+
+;; Helper: expect a type error containing `sub`
+(define
+  hk-tc-err
+  (fn
+    (label src sub)
+    (hk-test
+      label
+      (guard
+        (e (#t (hk-str-has? e sub)))
+        (begin (hk-run-typed src) false))
+      true)))
+
+;; ─── Valid programs pass through ─────────────────────────────────────────────
+(hk-test "typed ok: simple arithmetic" (hk-run-typed "main = 1 + 2") 3)
+
+(hk-test "typed ok: boolean" (hk-run-typed "main = True") (list "True"))
+
+(hk-test "typed ok: let binding" (hk-run-typed "main = let x = 1 in x + 2") 3)
+
+(hk-test
+  "typed ok: two independent fns"
+  (hk-run-typed "f x = x + 1\nmain = f 5")
+  6)
+
+;; ─── Untypeable programs are rejected ────────────────────────────────────────
+;; Adding Int and Bool is a unification failure.
+(hk-tc-err "reject: Int + Bool mentions Int" "main = 1 + True" "Int")
+(hk-tc-err "reject: Int + Bool mentions Bool" "main = 1 + True" "Bool")
+
+;; Condition of if must be Bool.
+(hk-tc-err "reject: if non-bool condition" "main = if 1 then 2 else 3" "Bool")
+
+;; Unbound variable.
+(hk-tc-err "reject: unbound variable" "main = unknownVar + 1" "unknownVar")
+
+;; Function body type error: applying non-function.
+(hk-tc-err "reject: apply non-function" "f x = 1 x" "Int")
+
+{:fails hk-test-fails :pass hk-test-pass :fail hk-test-fail}