Re: [Haskell-cafe] casting numerical types

Ok. I was hoping that there was a common ancestor of Integral and Fractional. Now I realize that I can be more precise about what I wanted: avg :: (FractionalOrIntegral a) => [a] -> a avg xs = sum (map fromFractionalOrIntegral xs) / (fromIntegral (length xs)) But although it there may be a sound type system supporting this it looks a little weird... thanks, matthias On Sat, Apr 01, 2006 at 06:10:48PM -0500, Cale Gibbard wrote:

To: Matthias Fischmann Cc: haskell-cafe@haskell.org From: Cale Gibbard Date: Sat, 1 Apr 2006 18:10:48 -0500 Subject: Re: [Haskell-cafe] casting numerical types

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 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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