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|
{-# OPTIONS_GHC -w #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and fix
-- any warnings in the module. See
-- http://hackage.haskell.org/trac/ghc/wiki/WorkingConventions#Warnings
-- for details
module State where
newtype State s a
= State
{ runState' :: s -> (# a, s #) }
instance Monad (State s) where
return x = State $ \s -> (# x, s #)
m >>= n = State $ \s ->
case runState' m s of
(# r, s' #) -> runState' (n r) s'
get :: State s s
get = State $ \s -> (# s, s #)
gets :: (s -> a) -> State s a
gets f = State $ \s -> (# f s, s #)
put :: s -> State s ()
put s' = State $ \s -> (# (), s' #)
modify :: (s -> s) -> State s ()
modify f = State $ \s -> (# (), f s #)
evalState :: State s a -> s -> a
evalState s i
= case runState' s i of
(# a, s' #) -> a
execState :: State s a -> s -> s
execState s i
= case runState' s i of
(# a, s' #) -> s'
runState :: State s a -> s -> (a, s)
runState s i
= case runState' s i of
(# a, s' #) -> (a, s')
mapAccumLM
:: Monad m
=> (acc -> x -> m (acc, y)) -- ^ combining funcction
-> acc -- ^ initial state
-> [x] -- ^ inputs
-> m (acc, [y]) -- ^ final state, outputs
mapAccumLM _ s [] = return (s, [])
mapAccumLM f s (x:xs)
= do
(s1, x') <- f s x
(s2, xs') <- mapAccumLM f s1 xs
return (s2, x' : xs')
|
