Add test for Trac #1564

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

@@ -247,6 +247,7 @@ test('tc231', normal, compile, [''])
 test('tc232', reqlib('mtl'), compile, [''])
 test('tc233', normal, compile, [''])
 test('tc234', normal, compile, [''])
+test('tc235', normal, compile, [''])
 
 test('faxen', normal, compile, [''])
 

testsuite/tests/ghc-regress/typecheck/should_compile/tc235.hs

+{-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-}
+
+-- Trac #1564
+
+module Foo where
+
+import Text.PrettyPrint
+import Prelude hiding(head,tail)
+
+class FooBar m k l | m -> k l where 
+ a :: m graphtype
+
+instance FooBar [] Bool Bool where
+  a = error "urk"
+
+instance FooBar Maybe Int Int where
+  a = error "urk"
+
+class (Monad m)=>Gr g ep m | g -> ep where 
+ x:: m Int
+ v:: m Int
+
+instance (Monad m,  FooBar m x z) =>  Gr g ep m  where
+  x = error "urk"
+  v = error "urk"  
+
+-- Old GHC claims for y:  y :: (Monad m, FooBar m GHC.Prim.Any GHC.Prim.Any)
+--			    => m Int (which is wrong)
+-- The uses in foo and bar show if that happens
+y () = x
+
+foo :: [Int]
+foo = y ()
+
+bar :: Maybe Int
+bar = y ()
+
+