[Haskell-cafe] casting numerical types

[Cale Gibbard]

Arbitrary numerical types don't support division. (They're rings, not
fields.) The
(Fractional a) => [a] -> a
type is the best you can do.

 - Cale

On 01/04/06, Matthias Fischmann <fis at wiwi.hu-berlin.de> wrote:
>
>
> hi all,
>
> this should be a quick one (for now I would be happy with a "that's
> impossible", just want to make sure I don't miss anything).  I want to
> compute the average from a list of arbitrary numerical element type.
> I wanted to do this:
>
>     avg :: (Num a) => [a] -> a
>     avg xs = sum (map fromNum xs) / (fromIntegral (length xs))
>
> but it doesn't compile.  All I could get to work is this:
>
>     avg :: (Fractional a) => [a] -> a
>     avg xs = sum xs / (fromIntegral (length xs))
>
>     avgI :: (Integral a) => [a] -> Float
>     avgI = avg . map fromIntegral
>
> The two function names for the same thing are tolerable, but not very
> elegant.  Is there another option?
>
> Thanks,
> Matthias
>
>
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> =mmOH
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>
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