2011/4/4 Daniel Fischer
On Monday 04 April 2011 17:15:20, Nadav Chernin wrote:
Hello,
I tried to write function mean - average of numeric list.
mean::(Fractional a)=>[a]->a mean a = (realToFrac (sum a)) / (realToFrac (length a))
But error occures:
Could not deduce (Real a) from the context (Fractional b) arising from a use of `realToFrac' To correct this function, i rewrite this function:
mean::(Real a, Fractional a)=>[a]->b mean a = (realToFrac (sum a)) / (realToFrac (length a))
Is there most simple way to write this function?
For simple functions it is often revealing to define it in ghci and only then ask its type: -- your version: Prelude> let m2 as = (realToFrac $ sum as) / (realToFrac $ length as) Prelude> :t m2 m2 :: (Real a, Fractional b) => [a] -> b -- Daniel's version: Prelude> let m1 as = sum as / (fromIntegral $ length as) Prelude> :t m1 m1 :: (Fractional b) => [b] -> b