{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE ExplicitForAll #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableInstances #-}

{- | A carrier for the 'State' effect. It evaluates its inner state strictly, which is the correct choice for the majority of use cases.

Note that the parameter order in 'runState', 'evalState', and 'execState' is reversed compared the equivalent functions provided by @transformers@. This is an intentional decision made to enable the composition of effect handlers with '.' without invoking 'flip'.

@since 1.0.0.0
-}
module Control.Carrier.State.Strict
( -- * Strict state carrier
  runState
, evalState
, execState
, StateC(..)
  -- * State effect
, module Control.Effect.State
) where

import           Control.Algebra
import           Control.Applicative (Alternative(..))
import           Control.Effect.State
import           Control.Monad (MonadPlus(..))
import qualified Control.Monad.Fail as Fail
import           Control.Monad.Fix
import           Control.Monad.IO.Class
import           Control.Monad.Trans.Class

-- | Run a 'State' effect starting from the passed value.
--
-- @
-- 'runState' s ('pure' a) = 'pure' (s, a)
-- @
-- @
-- 'runState' s 'get' = 'pure' (s, s)
-- @
-- @
-- 'runState' s ('put' t) = 'pure' (t, ())
-- @
--
-- @since 1.0.0.0
runState :: s -> StateC s m a -> m (s, a)
runState :: s -> StateC s m a -> m (s, a)
runState s :: s
s (StateC runStateC :: s -> m (s, a)
runStateC) = s -> m (s, a)
runStateC s
s
{-# INLINE[3] runState #-}

-- | Run a 'State' effect, yielding the result value and discarding the final state.
--
-- @
-- 'evalState' s m = 'fmap' 'snd' ('runState' s m)
-- @
--
-- @since 1.0.0.0
evalState :: forall s m a . Functor m => s -> StateC s m a -> m a
evalState :: s -> StateC s m a -> m a
evalState s :: s
s = ((s, a) -> a) -> m (s, a) -> m a
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (s, a) -> a
forall a b. (a, b) -> b
snd (m (s, a) -> m a)
-> (StateC s m a -> m (s, a)) -> StateC s m a -> m a
forall b c a. (b -> c) -> (a -> b) -> a -> c
. s -> StateC s m a -> m (s, a)
forall s (m :: * -> *) a. s -> StateC s m a -> m (s, a)
runState s
s
{-# INLINE[3] evalState #-}

-- | Run a 'State' effect, yielding the final state and discarding the return value.
--
-- @
-- 'execState' s m = 'fmap' 'fst' ('runState' s m)
-- @
--
-- @since 1.0.0.0
execState :: forall s m a . Functor m => s -> StateC s m a -> m s
execState :: s -> StateC s m a -> m s
execState s :: s
s = ((s, a) -> s) -> m (s, a) -> m s
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (s, a) -> s
forall a b. (a, b) -> a
fst (m (s, a) -> m s)
-> (StateC s m a -> m (s, a)) -> StateC s m a -> m s
forall b c a. (b -> c) -> (a -> b) -> a -> c
. s -> StateC s m a -> m (s, a)
forall s (m :: * -> *) a. s -> StateC s m a -> m (s, a)
runState s
s
{-# INLINE[3] execState #-}


-- | @since 1.0.0.0
newtype StateC s m a = StateC (s -> m (s, a))
  deriving (a -> StateC s m b -> StateC s m a
(a -> b) -> StateC s m a -> StateC s m b
(forall a b. (a -> b) -> StateC s m a -> StateC s m b)
-> (forall a b. a -> StateC s m b -> StateC s m a)
-> Functor (StateC s m)
forall a b. a -> StateC s m b -> StateC s m a
forall a b. (a -> b) -> StateC s m a -> StateC s m b
forall s (m :: * -> *) a b.
Functor m =>
a -> StateC s m b -> StateC s m a
forall s (m :: * -> *) a b.
Functor m =>
(a -> b) -> StateC s m a -> StateC s m b
forall (f :: * -> *).
(forall a b. (a -> b) -> f a -> f b)
-> (forall a b. a -> f b -> f a) -> Functor f
<$ :: a -> StateC s m b -> StateC s m a
$c<$ :: forall s (m :: * -> *) a b.
Functor m =>
a -> StateC s m b -> StateC s m a
fmap :: (a -> b) -> StateC s m a -> StateC s m b
$cfmap :: forall s (m :: * -> *) a b.
Functor m =>
(a -> b) -> StateC s m a -> StateC s m b
Functor)

instance Monad m => Applicative (StateC s m) where
  pure :: a -> StateC s m a
pure a :: a
a = (s -> m (s, a)) -> StateC s m a
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC (\ s :: s
s -> (s, a) -> m (s, a)
forall (f :: * -> *) a. Applicative f => a -> f a
pure (s
s, a
a))
  {-# INLINE pure #-}
  StateC f :: s -> m (s, a -> b)
f <*> :: StateC s m (a -> b) -> StateC s m a -> StateC s m b
<*> StateC a :: s -> m (s, a)
a = (s -> m (s, b)) -> StateC s m b
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC ((s -> m (s, b)) -> StateC s m b)
-> (s -> m (s, b)) -> StateC s m b
forall a b. (a -> b) -> a -> b
$ \ s :: s
s -> do
    (s' :: s
s', f' :: a -> b
f') <- s -> m (s, a -> b)
f s
s
    (s'' :: s
s'', a' :: a
a') <- s -> m (s, a)
a s
s'
    (s, b) -> m (s, b)
forall (f :: * -> *) a. Applicative f => a -> f a
pure (s
s'', a -> b
f' a
a')
  {-# INLINE (<*>) #-}
  m :: StateC s m a
m *> :: StateC s m a -> StateC s m b -> StateC s m b
*> k :: StateC s m b
k = StateC s m a
m StateC s m a -> (a -> StateC s m b) -> StateC s m b
forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
>>= StateC s m b -> a -> StateC s m b
forall a b. a -> b -> a
const StateC s m b
k
  {-# INLINE (*>) #-}

instance (Alternative m, Monad m) => Alternative (StateC s m) where
  empty :: StateC s m a
empty = (s -> m (s, a)) -> StateC s m a
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC (m (s, a) -> s -> m (s, a)
forall a b. a -> b -> a
const m (s, a)
forall (f :: * -> *) a. Alternative f => f a
empty)
  {-# INLINE empty #-}
  StateC l :: s -> m (s, a)
l <|> :: StateC s m a -> StateC s m a -> StateC s m a
<|> StateC r :: s -> m (s, a)
r = (s -> m (s, a)) -> StateC s m a
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC (\ s :: s
s -> s -> m (s, a)
l s
s m (s, a) -> m (s, a) -> m (s, a)
forall (f :: * -> *) a. Alternative f => f a -> f a -> f a
<|> s -> m (s, a)
r s
s)
  {-# INLINE (<|>) #-}

instance Monad m => Monad (StateC s m) where
  StateC m :: s -> m (s, a)
m >>= :: StateC s m a -> (a -> StateC s m b) -> StateC s m b
>>= f :: a -> StateC s m b
f = (s -> m (s, b)) -> StateC s m b
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC ((s -> m (s, b)) -> StateC s m b)
-> (s -> m (s, b)) -> StateC s m b
forall a b. (a -> b) -> a -> b
$ \ s :: s
s -> do
    (s' :: s
s', a :: a
a) <- s -> m (s, a)
m s
s
    s -> StateC s m b -> m (s, b)
forall s (m :: * -> *) a. s -> StateC s m a -> m (s, a)
runState s
s' (a -> StateC s m b
f a
a)
  {-# INLINE (>>=) #-}

instance Fail.MonadFail m => Fail.MonadFail (StateC s m) where
  fail :: String -> StateC s m a
fail s :: String
s = (s -> m (s, a)) -> StateC s m a
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC (m (s, a) -> s -> m (s, a)
forall a b. a -> b -> a
const (String -> m (s, a)
forall (m :: * -> *) a. MonadFail m => String -> m a
Fail.fail String
s))
  {-# INLINE fail #-}

instance MonadFix m => MonadFix (StateC s m) where
  mfix :: (a -> StateC s m a) -> StateC s m a
mfix f :: a -> StateC s m a
f = (s -> m (s, a)) -> StateC s m a
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC (\ s :: s
s -> ((s, a) -> m (s, a)) -> m (s, a)
forall (m :: * -> *) a. MonadFix m => (a -> m a) -> m a
mfix (s -> StateC s m a -> m (s, a)
forall s (m :: * -> *) a. s -> StateC s m a -> m (s, a)
runState s
s (StateC s m a -> m (s, a))
-> ((s, a) -> StateC s m a) -> (s, a) -> m (s, a)
forall b c a. (b -> c) -> (a -> b) -> a -> c
. a -> StateC s m a
f (a -> StateC s m a) -> ((s, a) -> a) -> (s, a) -> StateC s m a
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (s, a) -> a
forall a b. (a, b) -> b
snd))
  {-# INLINE mfix #-}

instance MonadIO m => MonadIO (StateC s m) where
  liftIO :: IO a -> StateC s m a
liftIO io :: IO a
io = (s -> m (s, a)) -> StateC s m a
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC (\ s :: s
s -> (,) s
s (a -> (s, a)) -> m a -> m (s, a)
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> IO a -> m a
forall (m :: * -> *) a. MonadIO m => IO a -> m a
liftIO IO a
io)
  {-# INLINE liftIO #-}

instance (Alternative m, Monad m) => MonadPlus (StateC s m)

instance MonadTrans (StateC s) where
  lift :: m a -> StateC s m a
lift m :: m a
m = (s -> m (s, a)) -> StateC s m a
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC (\ s :: s
s -> (,) s
s (a -> (s, a)) -> m a -> m (s, a)
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> m a
m)
  {-# INLINE lift #-}

instance (Algebra sig m, Effect sig) => Algebra (State s :+: sig) (StateC s m) where
  alg :: (:+:) (State s) sig (StateC s m) a -> StateC s m a
alg (L (Get   k :: s -> StateC s m a
k)) = (s -> m (s, a)) -> StateC s m a
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC (\ s :: s
s -> s -> StateC s m a -> m (s, a)
forall s (m :: * -> *) a. s -> StateC s m a -> m (s, a)
runState s
s (s -> StateC s m a
k s
s))
  alg (L (Put s :: s
s k :: StateC s m a
k)) = (s -> m (s, a)) -> StateC s m a
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC (\ _ -> s -> StateC s m a -> m (s, a)
forall s (m :: * -> *) a. s -> StateC s m a -> m (s, a)
runState s
s StateC s m a
k)
  alg (R other :: sig (StateC s m) a
other)     = (s -> m (s, a)) -> StateC s m a
forall s (m :: * -> *) a. (s -> m (s, a)) -> StateC s m a
StateC (\ s :: s
s -> sig m (s, a) -> m (s, a)
forall (sig :: (* -> *) -> * -> *) (m :: * -> *) a.
Algebra sig m =>
sig m a -> m a
alg ((s, ())
-> (forall x. (s, StateC s m x) -> m (s, x))
-> sig (StateC s m) a
-> sig m (s, a)
forall (sig :: (* -> *) -> * -> *) (ctx :: * -> *) (m :: * -> *)
       (n :: * -> *) a.
(Effect sig, Functor ctx, Monad m) =>
ctx ()
-> (forall x. ctx (m x) -> n (ctx x)) -> sig m a -> sig n (ctx a)
thread (s
s, ()) ((s -> StateC s m x -> m (s, x)) -> (s, StateC s m x) -> m (s, x)
forall a b c. (a -> b -> c) -> (a, b) -> c
uncurry s -> StateC s m x -> m (s, x)
forall s (m :: * -> *) a. s -> StateC s m a -> m (s, a)
runState) sig (StateC s m) a
other))
  {-# INLINE alg #-}