[Haskell-cafe] Principal type in Haskell
haskelllist at hotmail.com
Thu Jun 22 05:22:32 EDT 2006
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?
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