[Haskell-cafe] Principal type in Haskell

[william kim]

Hi All,

I am confused by the notion of principal type in Haskell with type classes. 
Consider a simple example:

f x y = [x] == [y]

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?

Thanks.

william

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