On 03/03/07, Bryan Burgers wrote:

As far as I know, you should be defining the type of bar in the class declaration for Foo, not in an instance declaration.

I think I over-reduced my problem. Here's a more complex issue that can't be resolved by moving bar to be a method of the class: {-# OPTIONS_GHC -fglasgow-exts #-} class Foo a b | a -> b where foo :: Foo b c => a -> Maybe c instance Foo String () where foo _ = Nothing instance Foo Int String where foo 4 = Just (); foo _ = Nothing -- -David House, dmhouse@gmail.com