test.hs:8:10:
Could not deduce (Fractional a)
from the context (Num a, Fractional b)
arising from a use of `/' at test.hs:8:10-42
Possible fix:
add (Fractional a) to the context of the type signature for `mean'
In the expression: sum xs / fromIntegral (length xs)
In the definition of `mean':
mean xs = sum xs / fromIntegral (length xs)
test.hs:8:10:
Couldn't match expected type `b' against inferred type `a'
`b' is a rigid type variable bound by
the type signature for `mean' at test.hs:7:27
`a' is a rigid type variable bound by
the type signature for `mean' at test.hs:7:13
In the expression: sum xs / fromIntegral (length xs)
In the definition of `mean':
mean xs = sum xs / fromIntegral (length xs)
And the div way will do integer division, which is not what I want.
On Fri, Jul 1, 2011 at 2:07 PM, Nathan Howell
<nathan.d.howell@gmail.com> wrote:
(/) 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
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.