haskell: type-sig checking — hk-ast-type + hk-check-sig + sig-aware infer-prog (+6 tests, 470/470)

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

lib/haskell/tests/typecheck.sx

@@ -41,4 +41,42 @@
 ;; Function body type error: applying non-function.
 (hk-tc-err "reject: apply non-function" "f x = 1 x" "Int")
 
+(define prog-sig1 (hk-core "f :: Int -> Int\nf x = x + 1"))
+
+(define prog-sig2 (hk-core "f :: Bool -> Bool\nf x = x + 1"))
+
+(define prog-sig3 (hk-core "id :: a -> a\nid x = x"))
+
+(hk-test
+  "sig ok: Int->Int accepted"
+  (first (nth (hk-infer-prog prog-sig1 (hk-type-env0)) 0))
+  "ok")
+
+(hk-test
+  "sig fail: Bool->Bool rejected"
+  (first (nth (hk-infer-prog prog-sig2 (hk-type-env0)) 0))
+  "err")
+
+(hk-test
+  "sig fail: error mentions mismatch"
+  (hk-str-has?
+    (nth (nth (hk-infer-prog prog-sig2 (hk-type-env0)) 0) 1)
+    "mismatch")
+  true)
+
+(hk-test
+  "sig ok: polymorphic a->a accepted"
+  (first (nth (hk-infer-prog prog-sig3 (hk-type-env0)) 0))
+  "ok")
+
+(hk-tc-err
+  "run-typed sig fail: Bool declared, Int inferred"
+  "main :: Bool\nmain = 1 + 2"
+  "mismatch")
+
+(hk-test
+  "run-typed sig ok: Int declared matches"
+  (hk-run-typed "main :: Int\nmain = 1 + 2")
+  3)
+
 {:fails hk-test-fails :pass hk-test-pass :fail hk-test-fail}