haskell: dict-passing elaborator — runtime dispatch via hk-mk-lazy-builtin (+3 tests, 506/506)

lib/haskell/tests/class.sx

@@ -32,4 +32,29 @@
   (has-key? (get env-full "dictMyEq_Int") "myEq")
   true)
 
+(hk-test
+  "dispatch: single-arg method works"
+  (hk-deep-force
+    (hk-run
+      "class Describable a where\n  describe :: a -> String\ninstance Describable Int where\n  describe x = \"an integer\"\nmain = describe 42"))
+  "an integer")
+
+(hk-test
+  "dispatch: second instance (Bool)"
+  (hk-deep-force
+    (hk-run
+      "class Describable a where\n  describe :: a -> String\ninstance Describable Bool where\n  describe x = \"a boolean\"\ninstance Describable Int where\n  describe x = \"an integer\"\nmain = describe True"))
+  "a boolean")
+
+(hk-test
+  "dispatch: error on unknown instance"
+  (guard
+    (e (true (>= (index-of e "No instance") 0)))
+    (begin
+      (hk-deep-force
+        (hk-run
+          "class Describable a where\n  describe :: a -> String\nmain = describe 42"))
+      false))
+  true)
+
 {:fails hk-test-fails :pass hk-test-pass :fail hk-test-fail}