import "Prelude" hiding (scanl)

scanl :: (b -> a -> <e> b) -> b -> [a] -> <e> [b]
scanl f initial l = build (loop initial 0)
  where
    len = length l
    loop cur i accum cons = let nl = cons accum cur
                            in if i==len
                               then nl
                               else loop (f cur (l!i)) (i+1) nl cons
                               
main = scanl (+) 0 [1,2,3]
--
[0, 1, 3, 6]