/usr/lib/hugs/packages/base/Control/Monad/ST/Lazy.hs is in libhugs-base-bundled 98.200609.21-5.3ubuntu1.
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-- |
-- 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
import Hugs.LazyST
instance MonadFix (ST s) where
mfix = fixST
-- ---------------------------------------------------------------------------
-- Strict <--> Lazy
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
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