Project Euler Problem 076

import Data.Array

countsums :: (Enum t, Num t, Num e, Ix t) => t -> e
countsums n = a!(n,n)
    where
      a = array ((0,0),(n,n)) $ ((0,0),1) 
          : [( (k,l), foldl (\c x -> c + (a!(k-x, min (k-x) x))) 0 [1..l])
               | k<-[1..n], l<-[1..k]]
ans1 :: Integer
ans1 = (subtract 1) . countsums $ 100
main :: IO ()
main = print ans1