What happens if you change the signature of meanList to meanList :: ( Fractional b) => [b] ->b The integrals in [1,2,3] would be converted to [1.0, 2.0, 3.0] before you act upon them. On 22 Sep 2016 6:49 p.m., "Lai Boon Hui" wrote: Hi, can someone explain to me why i cannot define meanList as: meanList :: (Integral a, Fractional b) => [a] -> a meanList xs = (sumList xs) / (lengthList xs) I want to restrict the function to only accept lists like [1,2,3] and return answer 2.0 sumList :: (Num a) => [a] -> a sumList [] = 0 sumList (x:xs) = x + (sumList xs) lengthList :: (Num a) => [t] -> a lengthList [] = 0 lengthList (_:xs) = 1 + (lengthList xs) _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners