Remove non-directory stuff (of base), and rename package to "directory"

[haskell-directory.git] / Control / Monad / ST / Lazy.hs

diff --git a/Control/Monad/ST/Lazy.hs b/Control/Monad/ST/Lazy.hs
deleted file mode 100644 (file)
index 5bf1265..0000000
--- a/Control/Monad/ST/Lazy.hs
+++ /dev/null
@@ -1,152 +0,0 @@
------------------------------------------------------------------------------
--- |
--- Module      :  Control.Monad.ST.Lazy
--- Copyright   :  (c) The University of Glasgow 2001
--- License     :  BSD-style (see the file libraries/base/LICENSE)
--- 
--- Maintainer  :  libraries@haskell.org
--- Stability   :  provisional
--- Portability :  non-portable (requires universal quantification for runST)
---
--- This module presents an identical interface to "Control.Monad.ST",
--- except that the monad delays evaluation of state operations until
--- a value depending on them is required.
---
------------------------------------------------------------------------------
-
-module Control.Monad.ST.Lazy (
-       -- * The 'ST' monad
-       ST,
-       runST,
-       fixST,
-
-       -- * Converting between strict and lazy 'ST'
-       strictToLazyST, lazyToStrictST,
-
-       -- * Converting 'ST' To 'IO'
-       RealWorld,
-       stToIO,
-
-       -- * Unsafe operations
-       unsafeInterleaveST,
-       unsafeIOToST
-    ) where
-
-import Prelude
-
-import Control.Monad.Fix
-
-import Control.Monad.ST (RealWorld)
-import qualified Control.Monad.ST as ST
-
-#ifdef __GLASGOW_HASKELL__
-import qualified GHC.ST
-import GHC.Base
-import Control.Monad
-#endif
-
-#ifdef __HUGS__
-import Hugs.LazyST
-#endif
-
-#ifdef __GLASGOW_HASKELL__
--- | The lazy state-transformer monad.
--- A computation of type @'ST' s a@ transforms an internal state indexed
--- by @s@, and returns a value of type @a@.
--- The @s@ parameter is either
---
--- * an unstantiated type variable (inside invocations of 'runST'), or
---
--- * 'RealWorld' (inside invocations of 'stToIO').
---
--- It serves to keep the internal states of different invocations of
--- 'runST' separate from each other and from invocations of 'stToIO'.
---
--- The '>>=' and '>>' operations are not strict in the state.  For example,
---
--- @'runST' (writeSTRef _|_ v >>= readSTRef _|_ >> return 2) = 2@
-newtype ST s a = ST (State s -> (a, State s))
-data State s = S# (State# s)
-
-instance Functor (ST s) where
-    fmap f m = ST $ \ s ->
-      let 
-       ST m_a = m
-       (r,new_s) = m_a s
-      in
-      (f r,new_s)
-
-instance Monad (ST s) where
-
-        return a = ST $ \ s -> (a,s)
-        m >> k   =  m >>= \ _ -> k
-       fail s   = error s
-
-        (ST m) >>= k
-         = ST $ \ s ->
-           let
-             (r,new_s) = m s
-             ST k_a = k r
-           in
-           k_a new_s
-
-{-# NOINLINE runST #-}
--- | Return the value computed by a state transformer computation.
--- The @forall@ ensures that the internal state used by the 'ST'
--- computation is inaccessible to the rest of the program.
-runST :: (forall s. ST s a) -> a
-runST st = case st of ST the_st -> let (r,_) = the_st (S# realWorld#) in r
-
--- | Allow the result of a state transformer computation to be used (lazily)
--- inside the computation.
--- Note that if @f@ is strict, @'fixST' f = _|_@.
-fixST :: (a -> ST s a) -> ST s a
-fixST m = ST (\ s -> 
-               let 
-                  ST m_r = m r
-                  (r,s') = m_r s
-               in
-                  (r,s'))
-#endif
-
-instance MonadFix (ST s) where
-       mfix = fixST
-
--- ---------------------------------------------------------------------------
--- Strict <--> Lazy
-
-#ifdef __GLASGOW_HASKELL__
-{-|
-Convert a strict 'ST' computation into a lazy one.  The strict state
-thread passed to 'strictToLazyST' is not performed until the result of
-the lazy state thread it returns is demanded.
--}
-strictToLazyST :: ST.ST s a -> ST s a
-strictToLazyST m = ST $ \s ->
-        let 
-          pr = case s of { S# s# -> GHC.ST.liftST m s# }
-          r  = case pr of { GHC.ST.STret _ v -> v }
-          s' = case pr of { GHC.ST.STret s2# _ -> S# s2# }
-       in
-       (r, s')
-
-{-| 
-Convert a lazy 'ST' computation into a strict one.
--}
-lazyToStrictST :: ST s a -> ST.ST s a
-lazyToStrictST (ST m) = GHC.ST.ST $ \s ->
-        case (m (S# s)) of (a, S# s') -> (# s', a #)
-
-unsafeInterleaveST :: ST s a -> ST s a
-unsafeInterleaveST = strictToLazyST . ST.unsafeInterleaveST . lazyToStrictST
-#endif
-
-unsafeIOToST :: IO a -> ST s a
-unsafeIOToST = strictToLazyST . ST.unsafeIOToST
-
--- | A monad transformer embedding lazy state transformers in the 'IO'
--- monad.  The 'RealWorld' parameter indicates that the internal state
--- used by the 'ST' computation is a special one supplied by the 'IO'
--- monad, and thus distinct from those used by invocations of 'runST'.
-stToIO :: ST RealWorld a -> IO a
-stToIO = ST.stToIO . lazyToStrictST