Edsko de Vries wrote:
sum :: Tree -> Int
sum t = sum' [t] 0
where
sum' [] acc = acc
sum' (Leaf i : ts) acc = sum' ts $! (i + acc)
sum' (Node l r : ts) acc = sum' (l : r : ts) acc
Because of $!, you should compare the Leaf case to foldl', not foldl. The Node case can be said to mimic a stack using heap resource. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
