[Haskell-cafe] How to implement the mean function

[Ruohao Li]

For mean xs = sum xs / length xs, I got the following:

test.hs:8:10:
    No instance for (Fractional Int)
      arising from a use of `/' at test.hs:8:10-27
    Possible fix: add an instance declaration for (Fractional Int)
    In the expression: sum xs / length xs
    In the definition of `mean': mean xs = sum xs / length xs

test.hs:8:10:
    Couldn't match expected type `b' against inferred type `Int'
      `b' is a rigid type variable bound by
          the type signature for `mean' at test.hs:7:27
    In the expression: sum xs / length xs
    In the definition of `mean': mean xs = sum xs / length xs

test.hs:8:19:
    Couldn't match expected type `a' against inferred type `Int'
      `a' is a rigid type variable bound by
          the type signature for `mean' at test.hs:7:13
    In the second argument of `(/)', namely `length xs'
    In the expression: sum xs / length xs
    In the definition of `mean': mean xs = sum xs / length xs
On Fri, Jul 1, 2011 at 2:00 PM, aditya siram <aditya.siram at gmail.com> wrote:

> What compiler errors are you getting?
> -deech
>
> On Fri, Jul 1, 2011 at 12:55 AM, 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.
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe at haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
> >
>
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