[Haskell-cafe] noob question

[Don Stewart]

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