thefunkslists:
I'm just starting to learn Haskell, and I'm having some confusion (I think) with how the type inference is working. Can someone explain why, in ghc 6.8.2 this works: *Main> (1/3)^3 3.7037037037037035e-2 But this doesn't *Main> (\k -> (1/k) ^ k) 3 <interactive>:1:8: Ambiguous type variable `t' in the constraints: `Fractional t' arising from a use of `/' at <interactive>:1:8-10 `Integral t' arising from a use of `^' at <interactive>:1:7-15 Probable fix: add a type signature that fixes these type variable(s)
Oh, this is just that the / constrains the type to be of class Fractional, while ^ only works on Integral values. Try: Prelude> (\k -> (1/k) ** k) 3 3.703703703703703e-2 Because: Prelude> :t (^) (^) :: (Integral b, Num a) => a -> b -> a Prelude> :t (**) (**) :: (Floating a) => a -> a -> a Cheers, Don