Re: [Haskell-cafe] polymorphic type

Wenduan,

What I thought at first the signature of plus should be: plus :: (a -> c, b -> d) -> Either a b -> Either c d?Anyone know where I was wrong?

Your initial thought was right: it should (a -> c, b -> d) -> Either a b -> Either c d Why didn't you just test it by feeding in to a compiler or interpreter; these are really useful, you know. ;) Besides...

case :: (a -> c,b -> c) -> Either a b -> c case (f, g) (Left x) = f x case (f, g) (Right x) = g x

You can't name your function case: it's a reserved word. You might want to check out the standard libraries: case' = uncurry either HTH, Stefan