I created this file by simplifying an error I was getting from a program that uses the Javascript types. If you remove the type signatures for f1 and f2 it compiles, but how do I fix the error I get when I compile with the signatures? module Main where type CPS c a = (a -> c) -> c class CNode a data TNode = TNode instance CNode TNode m :: TNode -> TNode -> Bool m a b = f1 b a $ \_ -> True f1 :: (CNode a, CNode b) => a -> b -> CPS c a f1 a b f = f2 a b $ \_ -> f a f2 :: (CNode a, CNode b) => a -> b -> CPS c a f2 a b f = f1 a b $ \_ -> f a This gives these messages: yhc -linkcore Browser3.hs Compiling Main ( Browser3.hs ) -- during after type inference/checking Error: No default for Main.CNode at 16:1-16:29.(Id 215,[(Id 200,Id 250)]) Error: No default for Main.CNode at 16:1-16:29.(Id 214,[(Id 200,Id 251)]) Error: No default for Main.CNode at 13:1-13:29.(Id 220,[(Id 200,Id 248)]) Error: No default for Main.CNode at 13:1-13:29.(Id 219,[(Id 200,Id 249)]) You can replace the CNode/TNode and CPS declarations with this: import DOM.Level1.Html import DOM.Level1.Dom import CPS same result.