1 -----------------------------------------------------------------------------
3 -- Module : Control.Monad.ST.Lazy
4 -- Copyright : (c) The University of Glasgow 2001
5 -- License : BSD-style (see the file libraries/core/LICENSE)
7 -- Maintainer : libraries@haskell.org
8 -- Stability : provisional
9 -- Portability : non-portable (requires universal quantification for runST)
11 -- $Id: Lazy.hs,v 1.3 2001/12/21 15:07:21 simonmar Exp $
13 -- This module presents an identical interface to Control.Monad.ST,
14 -- but the underlying implementation of the state thread is lazy.
16 -----------------------------------------------------------------------------
18 module Control.Monad.ST.Lazy (
26 newSTRef, readSTRef, writeSTRef,
29 newSTArray, readSTArray, writeSTArray, boundsSTArray,
30 thawSTArray, freezeSTArray, unsafeFreezeSTArray,
31 #ifdef __GLASGOW_HASKELL__
32 -- no 'good' reason, just doesn't support it right now.
36 ST.unsafeIOToST, ST.stToIO,
38 strictToLazyST, lazyToStrictST
43 import qualified Data.STRef as STRef
46 #ifdef __GLASGOW_HASKELL__
47 import qualified Control.Monad.ST as ST
48 import qualified GHC.Arr as STArray
49 import qualified GHC.ST
60 import PrelPrim ( unST
67 , primUnsafeFreezeArray
68 , primSizeMutableArray
75 #ifdef __GLASGOW_HASKELL__
76 newtype ST s a = ST (State s -> (a, State s))
77 data State s = S# (State# s)
81 newtype ST s a = ST (s -> (a,s))
84 instance Functor (ST s) where
85 fmap f m = ST $ \ s ->
92 instance Monad (ST s) where
94 return a = ST $ \ s -> (a,s)
95 m >> k = m >>= \ _ -> k
107 #ifdef __GLASGOW_HASKELL__
108 {-# NOINLINE runST #-}
109 runST :: (forall s. ST s a) -> a
110 runST st = case st of ST the_st -> let (r,_) = the_st (S# realWorld#) in r
114 runST :: (__forall s. ST s a) -> a
115 runST st = case st of ST the_st -> let (r,_) = the_st realWorld in r
116 where realWorld = error "runST: entered the RealWorld"
119 fixST :: (a -> ST s a) -> ST s a
127 -- ---------------------------------------------------------------------------
130 newSTRef :: a -> ST s (STRef.STRef s a)
131 readSTRef :: STRef.STRef s a -> ST s a
132 writeSTRef :: STRef.STRef s a -> a -> ST s ()
134 newSTRef = strictToLazyST . STRef.newSTRef
135 readSTRef = strictToLazyST . STRef.readSTRef
136 writeSTRef r a = strictToLazyST (STRef.writeSTRef r a)
138 -- --------------------------------------------------------------------------
141 newSTArray :: Ix ix => (ix,ix) -> elt -> ST s (STArray.STArray s ix elt)
142 readSTArray :: Ix ix => STArray.STArray s ix elt -> ix -> ST s elt
143 writeSTArray :: Ix ix => STArray.STArray s ix elt -> ix -> elt -> ST s ()
144 boundsSTArray :: Ix ix => STArray.STArray s ix elt -> (ix, ix)
145 thawSTArray :: Ix ix => Array ix elt -> ST s (STArray.STArray s ix elt)
146 freezeSTArray :: Ix ix => STArray.STArray s ix elt -> ST s (Array ix elt)
147 unsafeFreezeSTArray :: Ix ix => STArray.STArray s ix elt -> ST s (Array ix elt)
149 #ifdef __GLASGOW_HASKELL__
151 newSTArray ixs init = strictToLazyST (STArray.newSTArray ixs init)
153 readSTArray arr ix = strictToLazyST (STArray.readSTArray arr ix)
154 writeSTArray arr ix v = strictToLazyST (STArray.writeSTArray arr ix v)
155 boundsSTArray arr = STArray.boundsSTArray arr
156 thawSTArray arr = strictToLazyST (STArray.thawSTArray arr)
157 freezeSTArray arr = strictToLazyST (STArray.freezeSTArray arr)
158 unsafeFreezeSTArray arr = strictToLazyST (STArray.unsafeFreezeSTArray arr)
159 unsafeThawSTArray arr = strictToLazyST (STArray.unsafeThawSTArray arr)
164 newSTArray ixs elt = do
165 { arr <- strictToLazyST (primNewArray (rangeSize ixs) elt)
166 ; return (STArray ixs arr)
169 boundsSTArray (STArray ixs arr) = ixs
170 readSTArray (STArray ixs arr) ix
171 = strictToLazyST (primReadArray arr (index ixs ix))
172 writeSTArray (STArray ixs arr) ix elt
173 = strictToLazyST (primWriteArray arr (index ixs ix) elt)
174 freezeSTArray (STArray ixs arr) = do
175 { arr' <- strictToLazyST (primFreezeArray arr)
176 ; return (Array ixs arr')
179 unsafeFreezeSTArray (STArray ixs arr) = do
180 { arr' <- strictToLazyST (primUnsafeFreezeArray arr)
181 ; return (Array ixs arr')
184 thawSTArray (Array ixs arr) = do
185 { arr' <- strictToLazyST (primThawArray arr)
186 ; return (STArray ixs arr')
189 primFreezeArray :: PrimMutableArray s a -> ST.ST s (PrimArray a)
190 primFreezeArray arr = do
191 { let n = primSizeMutableArray arr
192 ; arr' <- primNewArray n arrEleBottom
193 ; mapM_ (copy arr arr') [0..n-1]
194 ; primUnsafeFreezeArray arr'
197 copy arr arr' i = do { x <- primReadArray arr i; primWriteArray arr' i x }
198 arrEleBottom = error "primFreezeArray: panic"
200 primThawArray :: PrimArray a -> ST.ST s (PrimMutableArray s a)
201 primThawArray arr = do
202 { let n = primSizeArray arr
203 ; arr' <- primNewArray n arrEleBottom
204 ; mapM_ (copy arr arr') [0..n-1]
208 copy arr arr' i = primWriteArray arr' i (primIndexArray arr i)
209 arrEleBottom = error "primFreezeArray: panic"
212 -- ---------------------------------------------------------------------------
215 #ifdef __GLASGOW_HASKELL__
216 strictToLazyST :: ST.ST s a -> ST s a
217 strictToLazyST m = ST $ \s ->
219 pr = case s of { S# s# -> GHC.ST.liftST m s# }
220 r = case pr of { GHC.ST.STret _ v -> v }
221 s' = case pr of { GHC.ST.STret s2# _ -> S# s2# }
225 lazyToStrictST :: ST s a -> ST.ST s a
226 lazyToStrictST (ST m) = GHC.ST.ST $ \s ->
227 case (m (S# s)) of (a, S# s') -> (# s', a #)
231 strictToLazyST :: ST.ST s a -> ST s a
232 strictToLazyST m = ST $ \s ->
241 lazyToStrictST :: ST s a -> ST.ST s a
242 lazyToStrictST (ST m) = mkST $ m
245 unsafeInterleaveST :: ST s a -> ST s a
246 unsafeInterleaveST = strictToLazyST . ST.unsafeInterleaveST . lazyToStrictST