Copyright	(c) The University of Glasgow 2001
License	BSD-style (see the file libraries/base/LICENSE)
Maintainer	libraries@haskell.org
Stability	experimental
Portability	non-portable (requires universal quantification for runST)
Safe Haskell	Trustworthy
Language	Haskell2010

Control.Monad.ST.Safe

Contents

Description

Deprecated: Safe is now the default, please use Control.Monad.ST instead

This library provides support forstrict state threads, as described in the PLDI '94 paper by John Launchbury and Simon Peyton JonesLazy Functional State Threads.

Safe API Only.

Synopsis

dataST s a
runST :: (forall s.ST s a) -> a
fixST :: (a ->ST s a) ->ST s a
dataRealWorld ::Type
stToIO ::ST RealWorld a ->IO a

The`ST` Monad

dataST s aSource #

The strict state-transformer monad. A computation of typeST s a transforms an internal state indexed bys, and returns a value of typea. Thes parameter is either

an uninstantiated type variable (inside invocations ofrunST), or
RealWorld (inside invocations ofstToIO).

It serves to keep the internal states of different invocations ofrunST separate from each other and from invocations ofstToIO.

The>>= and>> operations are strict in the state (though not in values stored in the state). For example,

runST (writeSTRef _|_ v >>= f) = _|_

Instances

Monad (ST s)Source #	Since: 2.1
Instance details Defined inGHC.ST Methods (>>=) ::ST s a -> (a ->ST s b) ->ST s bSource # (>>) ::ST s a ->ST s b ->ST s bSource # return :: a ->ST s aSource # fail ::String ->ST s aSource #
Functor (ST s)Source #	Since: 2.1
Instance details Defined inGHC.ST Methods fmap :: (a -> b) ->ST s a ->ST s bSource # (<$) :: a ->ST s b ->ST s aSource #
MonadFix (ST s)Source #	Since: 2.1
Instance details Defined inControl.Monad.Fix Methods mfix :: (a ->ST s a) ->ST s aSource #
MonadFail (ST s)Source #	Since: 4.11.0.0
Instance details Defined inGHC.ST Methods fail ::String ->ST s aSource #
Applicative (ST s)Source #	Since: 4.4.0.0
Instance details Defined inGHC.ST Methods pure :: a ->ST s aSource # (<>) ::ST s (a -> b) ->ST s a ->ST s bSource # liftA2 :: (a -> b -> c) ->ST s a ->ST s b ->ST s cSource # (>) ::ST s a ->ST s b ->ST s bSource # (<*) ::ST s a ->ST s b ->ST s aSource #
Show (ST s a)Source #	Since: 2.1
Instance details Defined inGHC.ST Methods showsPrec ::Int ->ST s a ->ShowS Source # show ::ST s a ->String Source # showList :: [ST s a] ->ShowS Source #
Semigroup a =>Semigroup (ST s a)Source #	Since: 4.11.0.0
Instance details Defined inGHC.ST Methods (<>) ::ST s a ->ST s a ->ST s aSource # sconcat ::NonEmpty (ST s a) ->ST s aSource # stimes ::Integral b => b ->ST s a ->ST s aSource #
Monoid a =>Monoid (ST s a)Source #	Since: 4.11.0.0
Instance details Defined inGHC.ST Methods mempty ::ST s aSource # mappend ::ST s a ->ST s a ->ST s aSource # mconcat :: [ST s a] ->ST s aSource #

runST :: (forall s.ST s a) -> aSource #

Return the value computed by a state transformer computation. Theforall ensures that the internal state used by theST computation is inaccessible to the rest of the program.

fixST :: (a ->ST s a) ->ST s aSource #

Allow the result of a state transformer computation to be used (lazily) inside the computation.

Note that iff is strict,fixST f = _|_.

Converting`ST` to`IO`

dataRealWorld ::Type #

RealWorld is deeply magical. It isprimitive, but it is notunlifted (henceptrArg). We never manipulate values of typeRealWorld; it's only used in the type system, to parameteriseState#.

stToIO ::ST RealWorld a ->IO aSource #

Embed a strict state transformer in anIO action. TheRealWorld parameter indicates that the internal state used by theST computation is a special one supplied by theIO monad, and thus distinct from those used by invocations ofrunST.

Movatterモバイル変換

TheST Monad

ConvertingST toIO

The`ST` Monad

Converting`ST` to`IO`