[Yhc] Incomprehensible error messages

[David Fox]

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.