On Thu, Nov 12, 2009 at 7:06 AM, Shawn Willden
Hmm. Would that also explain this?
Prelude> let f1 x = x * 2 Prelude> :type f1 f1 :: (Num a) => a -> a Prelude> let f2 = \x -> f1 x Prelude> :type f2 f2 :: Integer -> Integer
Yes, that's the same monomorphism restriction. Also, note that you are defaulting to Integer here: Prelude> :s -Wall Prelude> let f1 x = x * 2 Prelude> :t f1 f1 :: (Num a) => a -> a Prelude> let f2 = \x -> f1 x <interactive>:1:15: Warning: Defaulting the following constraint(s) to type `Integer' `Num a' arising from a use of `f1' at <interactive>:1:15-18 In the expression: f1 x In the expression: \ x -> f1 x In the definition of `f2': f2 = \ x -> f1 x Prelude> let f3 :: Int -> Int; f3 = \x -> f1 x Prelude> let f4 :: Num a => a -> a; f4 = \x -> f1 x I find -Wall very useful. Relatively few times it gets annoying. HTH, -- Felipe.