3Sum

import Data.List (nub, sort)

tsum' :: (Num a, Eq a) => [a] -> [a] -> [[a]]
tsum' x y
    | lenX < 3 && lenXY >= 3 = (tsum' (x ++ [headY]) tailY) ++ (tsum' x tailY)
    | lenX == 3 && (sum x) == 0 = [x]
    | otherwise = []
    where lenX = length x
          lenXY = lenX + length y
          headY = head y
          tailY = tail y

tsum :: (Ord a, Num a, Eq a) => [a] -> [[a]]
tsum x = nub (tsum' [] (sort x))