You probably don't want to use n+k patterns. Here is a clearer way to write it: factorial' :: Int -> Int factorial' 0 = 1 factorial' n = n*factorial' (n-1) Nick On Friday, August 31, 2012 12:30:34 PM Brandon Allbery wrote:

On Fri, Aug 31, 2012 at 12:23 PM, KMandPJLynch wrote:

...

*factorial' :: Int -> Int* *factorial' 0 = 1* *factorial' (n+1) = (n+1)*factorial' n*

n+k patterns were removed from Haskell 2010. You can re-enable them in GHC with

{-# LANGUAGE NPlusKPatterns #-}

or

{-# LANGUAGE Haskell98 #-}

as the first line of the source file.