Re: [Haskell-cafe] Principal type in Haskell

Hello william, Thursday, June 22, 2006, 1:22:32 PM, you wrote:

GHCi yields type f :: (Eq [a]) => a -> a -> Bool.

But according to the paper "Type classes: an exploration of the design space", predicate Eq [a] should be reduced to Eq a. Is this reduction performed here? What should be the principal type of f?

Ghc, unlike H98, supports instances like this: instance Eq [MyType] where a==b = True so this extension to type inference allows to use such instance even if MyType is not in Eq class -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com