content: {-# LANGUAGE CPP #-}
  #if __GLASGOW_HASKELL__ >= 702
  {-# LANGUAGE Safe #-}
  #endif
  #if __GLASGOW_HASKELL__ >= 710
  {-# LANGUAGE AutoDeriveTypeable #-}
  #endif
  -----------------------------------------------------------------------------
  -- |
  -- Module      :  Control.Monad.Trans.RWS.Strict
  -- Copyright   :  (c) Andy Gill 2001,
  --                (c) Oregon Graduate Institute of Science and Technology, 2001
  -- License     :  BSD-style (see the file LICENSE)
  --
  -- Maintainer  :  R.Paterson@city.ac.uk
  -- Stability   :  experimental
  -- Portability :  portable
  --
  -- A monad transformer that combines 'ReaderT', 'WriterT' and 'StateT'.
  -- This version is strict; for a lazy version with the same interface,
  -- see "Control.Monad.Trans.RWS.Lazy".
  -- Although the output is built strictly, it is not possible to
  -- achieve constant space behaviour with this transformer: for that,
  -- use "Control.Monad.Trans.RWS.CPS" instead.
  -----------------------------------------------------------------------------
  
  module Control.Monad.Trans.RWS.Strict (
      -- * The RWS monad
      RWS,
      rws,
      runRWS,
      evalRWS,
      execRWS,
      mapRWS,
      withRWS,
      -- * The RWST monad transformer
      RWST(..),
      evalRWST,
      execRWST,
      mapRWST,
      withRWST,
      -- * Reader operations
      reader,
      ask,
      local,
      asks,
      -- * Writer operations
      writer,
      tell,
      listen,
      listens,
      pass,
      censor,
      -- * State operations
      state,
      get,
      put,
      modify,
      gets,
      -- * Lifting other operations
      liftCallCC,
      liftCallCC',
      liftCatch,
    ) where
  
  import Control.Monad.IO.Class
  import Control.Monad.Signatures
  import Control.Monad.Trans.Class
  #if MIN_VERSION_base(4,12,0)
  import Data.Functor.Contravariant
  #endif
  import Data.Functor.Identity
  
  import Control.Applicative
  import Control.Monad
  #if MIN_VERSION_base(4,9,0)
  import qualified Control.Monad.Fail as Fail
  #endif
  import Control.Monad.Fix
  import Data.Monoid
  
  -- | A monad containing an environment of type @r@, output of type @w@
  -- and an updatable state of type @s@.
  type RWS r w s = RWST r w s Identity
  
  -- | Construct an RWS computation from a function.
  -- (The inverse of 'runRWS'.)
  rws :: (r -> s -> (a, s, w)) -> RWS r w s a
  rws f = RWST (\ r s -> Identity (f r s))
  {-# INLINE rws #-}
  
  -- | Unwrap an RWS computation as a function.
  -- (The inverse of 'rws'.)
  runRWS :: RWS r w s a -> r -> s -> (a, s, w)
  runRWS m r s = runIdentity (runRWST m r s)
  {-# INLINE runRWS #-}
  
  -- | Evaluate a computation with the given initial state and environment,
  -- returning the final value and output, discarding the final state.
  evalRWS :: RWS r w s a  -- ^RWS computation to execute
          -> r            -- ^initial environment
          -> s            -- ^initial value
          -> (a, w)       -- ^final value and output
  evalRWS m r s = let
      (a, _, w) = runRWS m r s
      in (a, w)
  {-# INLINE evalRWS #-}
  
  -- | Evaluate a computation with the given initial state and environment,
  -- returning the final state and output, discarding the final value.
  execRWS :: RWS r w s a  -- ^RWS computation to execute
          -> r            -- ^initial environment
          -> s            -- ^initial value
          -> (s, w)       -- ^final state and output
  execRWS m r s = let
      (_, s', w) = runRWS m r s
      in (s', w)
  {-# INLINE execRWS #-}
  
  -- | Map the return value, final state and output of a computation using
  -- the given function.
  --
  -- * @'runRWS' ('mapRWS' f m) r s = f ('runRWS' m r s)@
  mapRWS :: ((a, s, w) -> (b, s, w')) -> RWS r w s a -> RWS r w' s b
  mapRWS f = mapRWST (Identity . f . runIdentity)
  {-# INLINE mapRWS #-}
  
  -- | @'withRWS' f m@ executes action @m@ with an initial environment
  -- and state modified by applying @f@.
  --
  -- * @'runRWS' ('withRWS' f m) r s = 'uncurry' ('runRWS' m) (f r s)@
  withRWS :: (r' -> s -> (r, s)) -> RWS r w s a -> RWS r' w s a
  withRWS = withRWST
  {-# INLINE withRWS #-}
  
  -- ---------------------------------------------------------------------------
  -- | A monad transformer adding reading an environment of type @r@,
  -- collecting an output of type @w@ and updating a state of type @s@
  -- to an inner monad @m@.
  newtype RWST r w s m a = RWST { runRWST :: r -> s -> m (a, s, w) }
  
  -- | Evaluate a computation with the given initial state and environment,
  -- returning the final value and output, discarding the final state.
  evalRWST :: (Monad m)
           => RWST r w s m a      -- ^computation to execute
           -> r                   -- ^initial environment
           -> s                   -- ^initial value
           -> m (a, w)            -- ^computation yielding final value and output
  evalRWST m r s = do
      (a, _, w) <- runRWST m r s
      return (a, w)
  {-# INLINE evalRWST #-}
  
  -- | Evaluate a computation with the given initial state and environment,
  -- returning the final state and output, discarding the final value.
  execRWST :: (Monad m)
           => RWST r w s m a      -- ^computation to execute
           -> r                   -- ^initial environment
           -> s                   -- ^initial value
           -> m (s, w)            -- ^computation yielding final state and output
  execRWST m r s = do
      (_, s', w) <- runRWST m r s
      return (s', w)
  {-# INLINE execRWST #-}
  
  -- | Map the inner computation using the given function.
  --
  -- * @'runRWST' ('mapRWST' f m) r s = f ('runRWST' m r s)@
  mapRWST :: (m (a, s, w) -> n (b, s, w')) -> RWST r w s m a -> RWST r w' s n b
  mapRWST f m = RWST $ \ r s -> f (runRWST m r s)
  {-# INLINE mapRWST #-}
  
  -- | @'withRWST' f m@ executes action @m@ with an initial environment
  -- and state modified by applying @f@.
  --
  -- * @'runRWST' ('withRWST' f m) r s = 'uncurry' ('runRWST' m) (f r s)@
  withRWST :: (r' -> s -> (r, s)) -> RWST r w s m a -> RWST r' w s m a
  withRWST f m = RWST $ \ r s -> uncurry (runRWST m) (f r s)
  {-# INLINE withRWST #-}
  
  instance (Functor m) => Functor (RWST r w s m) where
      fmap f m = RWST $ \ r s ->
          fmap (\ (a, s', w) -> (f a, s', w)) $ runRWST m r s
      {-# INLINE fmap #-}
  
  instance (Monoid w, Functor m, Monad m) => Applicative (RWST r w s m) where
      pure a = RWST $ \ _ s -> return (a, s, mempty)
      {-# INLINE pure #-}
      RWST mf <*> RWST mx = RWST $ \ r s -> do
          (f, s', w)  <- mf r s
          (x, s'',w') <- mx r s'
          return (f x, s'', w `mappend` w')
      {-# INLINE (<*>) #-}
  
  instance (Monoid w, Functor m, MonadPlus m) => Alternative (RWST r w s m) where
      empty = RWST $ \ _ _ -> mzero
      {-# INLINE empty #-}
      RWST m <|> RWST n = RWST $ \ r s -> m r s `mplus` n r s
      {-# INLINE (<|>) #-}
  
  instance (Monoid w, Monad m) => Monad (RWST r w s m) where
  #if !(MIN_VERSION_base(4,8,0))
      return a = RWST $ \ _ s -> return (a, s, mempty)
      {-# INLINE return #-}
  #endif
      m >>= k  = RWST $ \ r s -> do
          (a, s', w)  <- runRWST m r s
          (b, s'',w') <- runRWST (k a) r s'
          return (b, s'', w `mappend` w')
      {-# INLINE (>>=) #-}
  #if !(MIN_VERSION_base(4,13,0))
      fail msg = RWST $ \ _ _ -> fail msg
      {-# INLINE fail #-}
  #endif
  
  #if MIN_VERSION_base(4,9,0)
  instance (Monoid w, Fail.MonadFail m) => Fail.MonadFail (RWST r w s m) where
      fail msg = RWST $ \ _ _ -> Fail.fail msg
      {-# INLINE fail #-}
  #endif
  
  instance (Monoid w, MonadPlus m) => MonadPlus (RWST r w s m) where
      mzero = RWST $ \ _ _ -> mzero
      {-# INLINE mzero #-}
      RWST m `mplus` RWST n = RWST $ \ r s -> m r s `mplus` n r s
      {-# INLINE mplus #-}
  
  instance (Monoid w, MonadFix m) => MonadFix (RWST r w s m) where
      mfix f = RWST $ \ r s -> mfix $ \ ~(a, _, _) -> runRWST (f a) r s
      {-# INLINE mfix #-}
  
  instance (Monoid w) => MonadTrans (RWST r w s) where
      lift m = RWST $ \ _ s -> do
          a <- m
          return (a, s, mempty)
      {-# INLINE lift #-}
  
  instance (Monoid w, MonadIO m) => MonadIO (RWST r w s m) where
      liftIO = lift . liftIO
      {-# INLINE liftIO #-}
  
  #if MIN_VERSION_base(4,12,0)
  instance Contravariant m => Contravariant (RWST r w s m) where
      contramap f m = RWST $ \r s ->
        contramap (\ (a, s', w) -> (f a, s', w)) $ runRWST m r s
      {-# INLINE contramap #-}
  #endif
  
  -- ---------------------------------------------------------------------------
  -- Reader operations
  
  -- | Constructor for computations in the reader monad (equivalent to 'asks').
  reader :: (Monoid w, Monad m) => (r -> a) -> RWST r w s m a
  reader = asks
  {-# INLINE reader #-}
  
  -- | Fetch the value of the environment.
  ask :: (Monoid w, Monad m) => RWST r w s m r
  ask = RWST $ \ r s -> return (r, s, mempty)
  {-# INLINE ask #-}
  
  -- | Execute a computation in a modified environment
  --
  -- * @'runRWST' ('local' f m) r s = 'runRWST' m (f r) s@
  local :: (r -> r) -> RWST r w s m a -> RWST r w s m a
  local f m = RWST $ \ r s -> runRWST m (f r) s
  {-# INLINE local #-}
  
  -- | Retrieve a function of the current environment.
  --
  -- * @'asks' f = 'liftM' f 'ask'@
  asks :: (Monoid w, Monad m) => (r -> a) -> RWST r w s m a
  asks f = RWST $ \ r s -> return (f r, s, mempty)
  {-# INLINE asks #-}
  
  -- ---------------------------------------------------------------------------
  -- Writer operations
  
  -- | Construct a writer computation from a (result, output) pair.
  writer :: (Monad m) => (a, w) -> RWST r w s m a
  writer (a, w) = RWST $ \ _ s -> return (a, s, w)
  {-# INLINE writer #-}
  
  -- | @'tell' w@ is an action that produces the output @w@.
  tell :: (Monad m) => w -> RWST r w s m ()
  tell w = RWST $ \ _ s -> return ((),s,w)
  {-# INLINE tell #-}
  
  -- | @'listen' m@ is an action that executes the action @m@ and adds its
  -- output to the value of the computation.
  --
  -- * @'runRWST' ('listen' m) r s = 'liftM' (\\ (a, w) -> ((a, w), w)) ('runRWST' m r s)@
  listen :: (Monad m) => RWST r w s m a -> RWST r w s m (a, w)
  listen m = RWST $ \ r s -> do
      (a, s', w) <- runRWST m r s
      return ((a, w), s', w)
  {-# INLINE listen #-}
  
  -- | @'listens' f m@ is an action that executes the action @m@ and adds
  -- the result of applying @f@ to the output to the value of the computation.
  --
  -- * @'listens' f m = 'liftM' (id *** f) ('listen' m)@
  --
  -- * @'runRWST' ('listens' f m) r s = 'liftM' (\\ (a, w) -> ((a, f w), w)) ('runRWST' m r s)@
  listens :: (Monad m) => (w -> b) -> RWST r w s m a -> RWST r w s m (a, b)
  listens f m = RWST $ \ r s -> do
      (a, s', w) <- runRWST m r s
      return ((a, f w), s', w)
  {-# INLINE listens #-}
  
  -- | @'pass' m@ is an action that executes the action @m@, which returns
  -- a value and a function, and returns the value, applying the function
  -- to the output.
  --
  -- * @'runRWST' ('pass' m) r s = 'liftM' (\\ ((a, f), w) -> (a, f w)) ('runRWST' m r s)@
  pass :: (Monad m) => RWST r w s m (a, w -> w) -> RWST r w s m a
  pass m = RWST $ \ r s -> do
      ((a, f), s', w) <- runRWST m r s
      return (a, s', f w)
  {-# INLINE pass #-}
  
  -- | @'censor' f m@ is an action that executes the action @m@ and
  -- applies the function @f@ to its output, leaving the return value
  -- unchanged.
  --
  -- * @'censor' f m = 'pass' ('liftM' (\\ x -> (x,f)) m)@
  --
  -- * @'runRWST' ('censor' f m) r s = 'liftM' (\\ (a, w) -> (a, f w)) ('runRWST' m r s)@
  censor :: (Monad m) => (w -> w) -> RWST r w s m a -> RWST r w s m a
  censor f m = RWST $ \ r s -> do
      (a, s', w) <- runRWST m r s
      return (a, s', f w)
  {-# INLINE censor #-}
  
  -- ---------------------------------------------------------------------------
  -- State operations
  
  -- | Construct a state monad computation from a state transformer function.
  state :: (Monoid w, Monad m) => (s -> (a,s)) -> RWST r w s m a
  state f = RWST $ \ _ s -> case f s of (a,s') -> return (a, s', mempty)
  {-# INLINE state #-}
  
  -- | Fetch the current value of the state within the monad.
  get :: (Monoid w, Monad m) => RWST r w s m s
  get = RWST $ \ _ s -> return (s, s, mempty)
  {-# INLINE get #-}
  
  -- | @'put' s@ sets the state within the monad to @s@.
  put :: (Monoid w, Monad m) => s -> RWST r w s m ()
  put s = RWST $ \ _ _ -> return ((), s, mempty)
  {-# INLINE put #-}
  
  -- | @'modify' f@ is an action that updates the state to the result of
  -- applying @f@ to the current state.
  --
  -- * @'modify' f = 'get' >>= ('put' . f)@
  modify :: (Monoid w, Monad m) => (s -> s) -> RWST r w s m ()
  modify f = RWST $ \ _ s -> return ((), f s, mempty)
  {-# INLINE modify #-}
  
  -- | Get a specific component of the state, using a projection function
  -- supplied.
  --
  -- * @'gets' f = 'liftM' f 'get'@
  gets :: (Monoid w, Monad m) => (s -> a) -> RWST r w s m a
  gets f = RWST $ \ _ s -> return (f s, s, mempty)
  {-# INLINE gets #-}
  
  -- | Uniform lifting of a @callCC@ operation to the new monad.
  -- This version rolls back to the original state on entering the
  -- continuation.
  liftCallCC :: (Monoid w) =>
      CallCC m (a,s,w) (b,s,w) -> CallCC (RWST r w s m) a b
  liftCallCC callCC f = RWST $ \ r s ->
      callCC $ \ c ->
      runRWST (f (\ a -> RWST $ \ _ _ -> c (a, s, mempty))) r s
  {-# INLINE liftCallCC #-}
  
  -- | In-situ lifting of a @callCC@ operation to the new monad.
  -- This version uses the current state on entering the continuation.
  liftCallCC' :: (Monoid w) =>
      CallCC m (a,s,w) (b,s,w) -> CallCC (RWST r w s m) a b
  liftCallCC' callCC f = RWST $ \ r s ->
      callCC $ \ c ->
      runRWST (f (\ a -> RWST $ \ _ s' -> c (a, s', mempty))) r s
  {-# INLINE liftCallCC' #-}
  
  -- | Lift a @catchE@ operation to the new monad.
  liftCatch :: Catch e m (a,s,w) -> Catch e (RWST r w s m) a
  liftCatch catchE m h =
      RWST $ \ r s -> runRWST m r s `catchE` \ e -> runRWST (h e) r s
  {-# INLINE liftCatch #-}
  