[Haskell-cafe] How to implement the mean function

[Nathan Howell]

(/) operates on a Fractional instance... but length returns an Int, which is
not a Fractional.

You can convert the Int to a Fractional instance:
mean xs = sum xs / fromIntegral (length xs)

or try an integer division:
mean xs = sum xs `div` length xs

-n

On Thu, Jun 30, 2011 at 10:55 PM, Ruohao Li <liruohao at gmail.com> wrote:

> Hi guys,
>
> I just started learning some Haskell. I want to implement a mean function
> to compute the mean of a list. The signature of the function is:
> mean :: (Num a, Fractional b) => [a] -> b
> But when I implement this simple function, the compiler keep whining at me
> on type errors. I know this is wrong:
> mean xs = sum xs / length xs
> But how to get it right? Thanks.
>
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