Test Trac #1624

testsuite/tests/ghc-regress/typecheck/should_run/T1624.hs

+{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances #-}
+
+module Main where
+
+class Foo a b | a -> b where
+    foo :: a -> Maybe b
+    foo x = Nothing
+
+    bar :: a -> b
+
+instance Foo (Maybe a) a where
+    bar (Just x) = x
+
+
+main = do { print (foo (Just 'x'))
+	  ; print (bar (Just 'y')) }

testsuite/tests/ghc-regress/typecheck/should_run/T1624.stdout

+Nothing
+'y'

testsuite/tests/ghc-regress/typecheck/should_run/all.T

@@ -65,3 +65,4 @@ test('tcrun040', normal, compile_and_run, [''])
 
 test('church', normal, compile_and_run, [''])
 test('testeq2', normal, compile_and_run, [''])
+test('T1624', normal, compile_and_run, [''])