forth at rc wk1

swapforth.hs

-- Control.Monad.State.Strict

import Control.Applicative (liftA3)
import Control.Monad (replicateM)
import Control.Monad.Trans.State

type Stack = List[Int]
pop :: State Stack Int
pop = state $ \x ->
  case x of
    head::tail -> (head, tail)
    _          -> (0, [])

swap = do
  a <- pop
  b <- pop
  _ <- push b
  _ <- push a