[Haskell-cafe] Principal type in Haskell
bulat.ziganshin at gmail.com
Thu Jun 22 06:28:14 EDT 2006
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
Bulat mailto:Bulat.Ziganshin at gmail.com
More information about the Haskell-Cafe