[Haskell-cafe] Rewrite this imperative in FP way

a = [1,1,1,1] b = [0,1,2,3] d = [0,0,0,0] for i in b: for j in c: if (i+j)<3: d[i+j] += a[i] My just work implementation in Haskell http://hpaste.org/57452 Another people implementation in Haskell with Monad and it turns out complex and very imperatively. http://hpaste.org/57358 Do you have any cool solution in FP way? Thanks. -Simon