files/practicum/StdStateMonad.icl

   1 implementation module StdStateMonad
   2
   3 import StdMonad
   4
   5 :: ST s a = ST (s -> (a, s))
   6
   7 instance return (ST s) where return x     = ST (\w = (x, w))
   8 instance >>=    (ST s) where >>= (ST f) g = ST (\w = let (a, w1) = f w
   9                                                       in unST (g a) w1
  10                                                )
  11
  12 mkST :: (s -> (a,s)) -> ST s a
  13 mkST f = ST f
  14
  15 unST :: (ST s a) -> s -> (a, s)
  16 unST (ST f) = f