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+{-# LANGUAGE CPP, MagicHash, UnboxedTuples, TypeFamilies #-}
+{-# LANGUAGE FlexibleContexts, FlexibleInstances, UndecidableInstances #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# OPTIONS_GHC -fno-warn-deprecations #-}
+
+-- |
+-- Module      : Control.Monad.Primitive
+-- Copyright   : (c) Roman Leshchinskiy 2009
+-- License     : BSD-style
+--
+-- Maintainer  : Roman Leshchinskiy <rl@cse.unsw.edu.au>
+-- Portability : non-portable
+--
+-- Primitive state-transformer monads
+--
+
+module Control.Monad.Primitive (
+  PrimMonad(..), RealWorld, primitive_,
+  PrimBase(..),
+  liftPrim, primToPrim, primToIO, primToST, ioToPrim, stToPrim,
+  unsafePrimToPrim, unsafePrimToIO, unsafePrimToST, unsafeIOToPrim,
+  unsafeSTToPrim, unsafeInlinePrim, unsafeInlineIO, unsafeInlineST,
+  touch, evalPrim
+) where
+
+import GHC.Prim   ( State#, RealWorld, touch# )
+import GHC.Base   ( unsafeCoerce#, realWorld# )
+#if MIN_VERSION_base(4,4,0)
+import GHC.Base   ( seq# )
+#else
+import Control.Exception (evaluate)
+#endif
+#if MIN_VERSION_base(4,2,0)
+import GHC.IO     ( IO(..) )
+#else
+import GHC.IOBase ( IO(..) )
+#endif
+import GHC.ST     ( ST(..) )
+
+import Control.Monad.Trans.Class (lift)
+#if !MIN_VERSION_base(4,8,0)
+import Data.Monoid (Monoid)
+#endif
+
+import Control.Monad.Trans.Cont     ( ContT    )
+import Control.Monad.Trans.Identity ( IdentityT (IdentityT) )
+import Control.Monad.Trans.List     ( ListT    )
+import Control.Monad.Trans.Maybe    ( MaybeT   )
+import Control.Monad.Trans.Error    ( ErrorT, Error)
+import Control.Monad.Trans.Reader   ( ReaderT  )
+import Control.Monad.Trans.State    ( StateT   )
+import Control.Monad.Trans.Writer   ( WriterT  )
+import Control.Monad.Trans.RWS      ( RWST     )
+
+#if MIN_VERSION_transformers(0,4,0)
+import Control.Monad.Trans.Except   ( ExceptT  )
+#endif
+
+#if MIN_VERSION_transformers(0,5,3)
+import Control.Monad.Trans.Accum    ( AccumT   )
+import Control.Monad.Trans.Select   ( SelectT  )
+#endif
+
+import qualified Control.Monad.Trans.RWS.Strict    as Strict ( RWST   )
+import qualified Control.Monad.Trans.State.Strict  as Strict ( StateT )
+import qualified Control.Monad.Trans.Writer.Strict as Strict ( WriterT )
+
+-- | Class of monads which can perform primitive state-transformer actions
+class Monad m => PrimMonad m where
+  -- | State token type
+  type PrimState m
+
+  -- | Execute a primitive operation
+  primitive :: (State# (PrimState m) -> (# State# (PrimState m), a #)) -> m a
+
+-- | Class of primitive monads for state-transformer actions.
+--
+-- Unlike 'PrimMonad', this typeclass requires that the @Monad@ be fully
+-- expressed as a state transformer, therefore disallowing other monad
+-- transformers on top of the base @IO@ or @ST@.
+--
+-- @since 0.6.0.0
+class PrimMonad m => PrimBase m where
+  -- | Expose the internal structure of the monad
+  internal :: m a -> State# (PrimState m) -> (# State# (PrimState m), a #)
+
+-- | Execute a primitive operation with no result
+primitive_ :: PrimMonad m
+              => (State# (PrimState m) -> State# (PrimState m)) -> m ()
+{-# INLINE primitive_ #-}
+primitive_ f = primitive (\s# ->
+    case f s# of
+        s'# -> (# s'#, () #))
+
+instance PrimMonad IO where
+  type PrimState IO = RealWorld
+  primitive = IO
+  {-# INLINE primitive #-}
+instance PrimBase IO where
+  internal (IO p) = p
+  {-# INLINE internal #-}
+
+-- | @since 0.6.3.0
+instance PrimMonad m => PrimMonad (ContT r m) where
+  type PrimState (ContT r m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+instance PrimMonad m => PrimMonad (IdentityT m) where
+  type PrimState (IdentityT m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+-- | @since 0.6.2.0
+instance PrimBase m => PrimBase (IdentityT m) where
+  internal (IdentityT m) = internal m
+  {-# INLINE internal #-}
+
+instance PrimMonad m => PrimMonad (ListT m) where
+  type PrimState (ListT m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+instance PrimMonad m => PrimMonad (MaybeT m) where
+  type PrimState (MaybeT m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+instance (Error e, PrimMonad m) => PrimMonad (ErrorT e m) where
+  type PrimState (ErrorT e m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+instance PrimMonad m => PrimMonad (ReaderT r m) where
+  type PrimState (ReaderT r m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+instance PrimMonad m => PrimMonad (StateT s m) where
+  type PrimState (StateT s m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+instance (Monoid w, PrimMonad m) => PrimMonad (WriterT w m) where
+  type PrimState (WriterT w m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+instance (Monoid w, PrimMonad m) => PrimMonad (RWST r w s m) where
+  type PrimState (RWST r w s m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+#if MIN_VERSION_transformers(0,4,0)
+instance PrimMonad m => PrimMonad (ExceptT e m) where
+  type PrimState (ExceptT e m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+#endif
+
+#if MIN_VERSION_transformers(0,5,3)
+-- | @since 0.6.3.0
+instance ( Monoid w
+         , PrimMonad m
+# if !(MIN_VERSION_base(4,8,0))
+         , Functor m
+# endif
+         ) => PrimMonad (AccumT w m) where
+  type PrimState (AccumT w m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+instance PrimMonad m => PrimMonad (SelectT r m) where
+  type PrimState (SelectT r m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+#endif
+
+instance PrimMonad m => PrimMonad (Strict.StateT s m) where
+  type PrimState (Strict.StateT s m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+instance (Monoid w, PrimMonad m) => PrimMonad (Strict.WriterT w m) where
+  type PrimState (Strict.WriterT w m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+instance (Monoid w, PrimMonad m) => PrimMonad (Strict.RWST r w s m) where
+  type PrimState (Strict.RWST r w s m) = PrimState m
+  primitive = lift . primitive
+  {-# INLINE primitive #-}
+
+instance PrimMonad (ST s) where
+  type PrimState (ST s) = s
+  primitive = ST
+  {-# INLINE primitive #-}
+instance PrimBase (ST s) where
+  internal (ST p) = p
+  {-# INLINE internal #-}
+
+-- | Lifts a 'PrimBase' into another 'PrimMonad' with the same underlying state
+-- token type.
+liftPrim
+  :: (PrimBase m1, PrimMonad m2, PrimState m1 ~ PrimState m2) => m1 a -> m2 a
+{-# INLINE liftPrim #-}
+liftPrim = primToPrim
+
+-- | Convert a 'PrimBase' to another monad with the same state token.
+primToPrim :: (PrimBase m1, PrimMonad m2, PrimState m1 ~ PrimState m2)
+        => m1 a -> m2 a
+{-# INLINE primToPrim #-}
+primToPrim m = primitive (internal m)
+
+-- | Convert a 'PrimBase' with a 'RealWorld' state token to 'IO'
+primToIO :: (PrimBase m, PrimState m ~ RealWorld) => m a -> IO a
+{-# INLINE primToIO #-}
+primToIO = primToPrim
+
+-- | Convert a 'PrimBase' to 'ST'
+primToST :: PrimBase m => m a -> ST (PrimState m) a
+{-# INLINE primToST #-}
+primToST = primToPrim
+
+-- | Convert an 'IO' action to a 'PrimMonad'.
+-- 
+-- @since 0.6.2.0
+ioToPrim :: (PrimMonad m, PrimState m ~ RealWorld) => IO a -> m a
+{-# INLINE ioToPrim #-}
+ioToPrim = primToPrim
+
+-- | Convert an 'ST' action to a 'PrimMonad'.
+--
+-- @since 0.6.2.0
+stToPrim :: PrimMonad m => ST (PrimState m) a -> m a
+{-# INLINE stToPrim #-}
+stToPrim = primToPrim
+
+-- | Convert a 'PrimBase' to another monad with a possibly different state
+-- token. This operation is highly unsafe!
+unsafePrimToPrim :: (PrimBase m1, PrimMonad m2) => m1 a -> m2 a
+{-# INLINE unsafePrimToPrim #-}
+unsafePrimToPrim m = primitive (unsafeCoerce# (internal m))
+
+-- | Convert any 'PrimBase' to 'ST' with an arbitrary state token. This
+-- operation is highly unsafe!
+unsafePrimToST :: PrimBase m => m a -> ST s a
+{-# INLINE unsafePrimToST #-}
+unsafePrimToST = unsafePrimToPrim
+
+-- | Convert any 'PrimBase' to 'IO'. This operation is highly unsafe!
+unsafePrimToIO :: PrimBase m => m a -> IO a
+{-# INLINE unsafePrimToIO #-}
+unsafePrimToIO = unsafePrimToPrim
+
+-- | Convert an 'ST' action with an arbitraty state token to any 'PrimMonad'.
+-- This operation is highly unsafe!
+-- 
+-- @since 0.6.2.0
+unsafeSTToPrim :: PrimMonad m => ST s a -> m a
+{-# INLINE unsafeSTToPrim #-}
+unsafeSTToPrim = unsafePrimToPrim
+
+-- | Convert an 'IO' action to any 'PrimMonad'. This operation is highly
+-- unsafe!
+--
+-- @since 0.6.2.0
+unsafeIOToPrim :: PrimMonad m => IO a -> m a
+{-# INLINE unsafeIOToPrim #-}
+unsafeIOToPrim = unsafePrimToPrim
+
+unsafeInlinePrim :: PrimBase m => m a -> a
+{-# INLINE unsafeInlinePrim #-}
+unsafeInlinePrim m = unsafeInlineIO (unsafePrimToIO m)
+
+unsafeInlineIO :: IO a -> a
+{-# INLINE unsafeInlineIO #-}
+unsafeInlineIO m = case internal m realWorld# of (# _, r #) -> r
+
+unsafeInlineST :: ST s a -> a
+{-# INLINE unsafeInlineST #-}
+unsafeInlineST = unsafeInlinePrim
+
+touch :: PrimMonad m => a -> m ()
+{-# INLINE touch #-}
+touch x = unsafePrimToPrim
+        $ (primitive (\s -> case touch# x s of { s' -> (# s', () #) }) :: IO ())
+
+-- | Create an action to force a value; generalizes 'Control.Exception.evaluate'
+--
+-- @since 0.6.2.0
+evalPrim :: forall a m . PrimMonad m => a -> m a
+#if MIN_VERSION_base(4,4,0)
+evalPrim a = primitive (\s -> seq# a s)
+#else
+-- This may or may not work so well, but there's probably nothing better to do.
+{-# NOINLINE evalPrim #-}
+evalPrim a = unsafePrimToPrim (evaluate a :: IO a)
+#endif