[Haskell-beginners] Help with types

Daniel Carrera daniel.carrera at theingots.org
Thu Apr 23 08:57:58 EDT 2009


I want to make a simple "average" function:

average xs = (sum xs)/(length xs)

When I try that on ghci I get the following error:

     No instance for (Fractional Int)
       arising from a use of `/' at <interactive>:1:17-36
     Possible fix: add an instance declaration for (Fractional Int)
     In the expression: (sum xs) / (length xs)
     In the definition of `average': average xs = (sum xs) / (length xs)

Ok, so 'sum' is of type (Num a => [a] -> a), length is of type ([a] -> 
Int) and (/) is of type (Fractional a => a -> a -> a). Can someone 
explain how I can "add an instance declaration" to my function so as to 
make all these types compatible?


More information about the Beginners mailing list