Project Euler Problem 046

primes :: [Integer]
primes = 2:f[3][3,5..] where
  f (x:xs) ys = ps ++ f(xs++ps) [z|z<-qs,z`rem`x/=0] where
    (ps,qs) = span (< x*x) ys
isPrime :: Integer -> Bool
isPrime nn = imp nn primes where    
  imp n (p:ps) = if n Bool
expressive n = any id [s+p==n |p<-takeWhile (