On Jul 1, 2011, at 2:07 AM, Ruohao Li wrote:
> 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@gmail.com> wrote:
> What compiler errors are you getting?
> -deech
>
> On Fri, Jul 1, 2011 at 12:55 AM, Ruohao Li <
liruohao@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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