Robert Ziemba wrote:
Can anyone help me understand the behavior of the following expressions in ghci? I was trying to construct a flipped function 'elem' that would accept a list of characters first but I ran into this problem with the type signature. Thank you.
Prelude Data.List Data.Char> :t elem elem :: (Eq a) => a -> [a] -> Bool -- OK Prelude Data.List Data.Char> :t (flip elem) (flip elem) :: (Eq a) => [a] -> a -> Bool -- OK this is what I want Prelude Data.List Data.Char> let fElem = (flip elem) Prelude Data.List Data.Char> :t fElem fElem :: [()] -> () -> Bool -- ?? Function will not accept a [Char]
I think its due to the monomorphism restriction. If you define it like Prelude> let fElem x = (flip elem) x Prelude> :t fElem fElem :: (Eq a) => [a] -> a -> Bool it works. For the details look at http://haskell.org/haskellwiki/Monomorphism_restriction ... or wait for another answer (which I think will come). Daniel.
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