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.
Prelude> :t (**)
(**) :: Floating a => a -> a -> a
On Mon, Nov 9, 2015 at 12:14 PM, Venu Chakravorty
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.
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On Sun, 8 Nov 2015 23:14:11 -0500
Venu Chakravorty
<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) ============================
Could somebody please throw some light?
Consider the types of both (^) and (/). Then take a look at https://www.haskell.org/onlinereport/haskell2010/haskell2x.png and compare with your error message. Note especially that there is no connection from Integral to Fractional or vice versa. As a solution use either the already suggested (**) or fromIntegral (mind the last subsection of https://www.haskell.org/onlinereport/haskell2010/haskellch6.html ) best, Max
participants (3)
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Max Voit -
Venu Chakravorty -
yi lu