module ST where

type ST s a = s -> (a, s)

unitST :: a -> ST s a
unitST a = \ s -> (a, s)

bindST :: ST s a -> (a -> ST s b) -> ST s b
m `bindST` k = \ s0 -> let { (a, s1) = m s0 } in k a s1

setXST :: x -> ST (x, y) ()
setXST v = \ (x, y) -> ((), (v, y)) 

setYST :: y -> ST (x, y) ()
setYST v = \ (x, y) -> ((), (x, v))

getXST :: () -> ST (x, y) x
getXST () = \ (x, y) -> (x, (x, y))

getYST :: () -> ST (x, y) y
getYST () = \ (x, y) -> (y, (x, y))