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module IOMonad (State, IO(..)) where
import IOMonadPrims
{- I use data instead of type so that IO can be abstract. For efficiency,
IO can be annotated as a strict constructor.
-}
type IO a = State -> (State, a)
data State = State
-- The rest of this file is unnecessary at the moment since
-- unitIO & bindIO are primitives and we're not using the rest of this
{- Implemented as a primitives:
bindIO :: IO a -> (a -> IO b) -> IO b
bindIO (IO m) (IO k) = IO (\s0 -> let (s1, a) = m s0 in k a s1) -}
unitIO :: a -> IO a
unitIO x = IO (\s -> (s, x))
-}
{- Not currently used:
pureIO :: IO a -> a
pureIO (IO m) = let (s, x) = m State in x
-- execIO executes a program of type IO ().
execIO :: IO () -> State
execIO (IO m) = let (s, x) = m State in s
infixr 1 =:
infixr 1 ?
-- assignment
(=:) :: a -> Var a -> IO ()
x =: v = IO (\s -> (update v x s, ()))
-- reader
(?) :: Var a -> (a -> IO b) -> IO b
v ? k = IO (\s -> (s, readVar v s)) `bindIO` k
-- new
newvar :: IO (Var a)
newvar = IO allocVar
instance Eq (Var a) where
x == y = eqVar x y
-}
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