Here's a recursive definition which is less cool but less 'magic' powerset :: [a] -> [[a]] powerset [] = [[]] powerset (x:xs) = yss +

Here's a recursive definition which is less cool but less 'magic' powerset :: [a] -> [[a]] powerset [] = [[]] powerset (x:xs) = yss ++ map (x:) yss where yss = powerset xs > powerset [1,2,3] [[],[3],[2],[2,3],[1],[1,3],[1,2],[1,2,3]]