Hello there, This is just some toy program I was trying. I fail to understand why this works: ============================= Prelude> zipWith (\ x y -> ((x ^ y) / (product [1..x]))) [1..3] [2,2,2] [1.0,2.0,1.5] ============================= and this does not: ============================= Prelude> zipWith (\ x y -> ((y ^ x) / (product [1..x]))) [1..3] [2,2,2] <interactive>:1:19: Ambiguous type variable `a' in the constraints: `Fractional a' arising from a use of `/' at <interactive>:1:19-44 `Integral a' arising from a use of `^' at <interactive>:1:20-24 Probable fix: add a type signature that fixes these type variable(s) ============================ Note that the "^" function has "x" and "y" flipped. :t (^) says: ============================ (^) :: (Num a, Integral b) => a -> b -> a ============================ Could somebody please throw some light? Thanks.