[Haskell-cafe] polymorphic type

[Stefan Holdermans]

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