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

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

p2_1 :: Pos (x, y) x
p2_1 = \ (x, y) -> (x, \ x1 -> (x1, y))
xP = p2_1
p2_2 :: Pos (x, y) y
p2_2 = \ (x, y) -> (y, \ y1 -> (x, y1))
yP = p2_2

p3_1 :: Pos (x, y, z) x
p3_1 = \ (x, y, z) -> (x, \ x1 -> (x1, y, z))
xT = p3_1

p3_2 :: Pos (x, y, z) y
p3_2 = \ (x, y, z) -> (y, \ y1 -> (x, y1, z))
yT = p3_2

p3_3 :: Pos (x, y, z) z
p3_3 = \ (x, y, z) -> (z, \ z1 -> (x, y, z1))
zT = p3_3

getST :: Pos s a -> ST s a
getST p = \ s -> (fst (p s), s)

setST :: Pos s a -> a -> ST s ()
setST p v = \ s -> ((), snd (p s) v)