haskell: class/instance declarations — parse + instance dict eval (+11 tests, 503/503)

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

lib/haskell/tests/class.sx

@@ -0,0 +1,35 @@
+;; class.sx — tests for class/instance parsing and evaluation.
+
+(define prog-class1 (hk-core "class MyEq a where\n  myEq :: a -> a -> Bool"))
+(define prog-inst1 (hk-core "instance MyEq Int where\n  myEq x y = x == y"))
+
+;; ─── class-decl AST ───────────────────────────────────────────────────────────
+(define cd1 (first (nth prog-class1 1)))
+(hk-test "class-decl tag" (first cd1) "class-decl")
+(hk-test "class-decl name" (nth cd1 1) "MyEq")
+(hk-test "class-decl tvar" (nth cd1 2) "a")
+(hk-test "class-decl methods" (len (nth cd1 3)) 1)
+
+;; ─── instance-decl AST ────────────────────────────────────────────────────────
+(define id1 (first (nth prog-inst1 1)))
+(hk-test "instance-decl tag" (first id1) "instance-decl")
+(hk-test "instance-decl class" (nth id1 1) "MyEq")
+(hk-test "instance-decl type tag" (first (nth id1 2)) "t-con")
+(hk-test "instance-decl type name" (nth (nth id1 2) 1) "Int")
+(hk-test "instance-decl method count" (len (nth id1 3)) 1)
+
+;; ─── eval: instance dict is built ────────────────────────────────────────────
+(define
+  prog-full
+  (hk-core
+    "class MyEq a where\n  myEq :: a -> a -> Bool\ninstance MyEq Int where\n  myEq x y = x == y"))
+(define env-full (hk-eval-program prog-full))
+
+(hk-test "instance dict in env" (has-key? env-full "dictMyEq_Int") true)
+
+(hk-test
+  "instance dict has method"
+  (has-key? (get env-full "dictMyEq_Int") "myEq")
+  true)
+
+{:fails hk-test-fails :pass hk-test-pass :fail hk-test-fail}