| 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 for strict state threads, as described in the PLDI '94 paper by John Launchbury and Simon Peyton Jones Lazy Functional State Threads.
Safe API Only.
The ST Monad
The strict ST monad.
 The ST monad allows for destructive updates, but is escapable (unlike IO).
 A computation of type ST s aa, and
 execute in "thread" s. The s parameter is either
- an uninstantiated 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 strict in the state (though not in
 values stored in the state).  For example,
runST (writeSTRef _|_ v >>= f) = _|_Instances
| MonadFail (ST s) # | Since: base-4.11.0.0 | 
| MonadFix (ST s) # | Since: base-2.1 | 
| Defined in Control.Monad.Fix | |
| Applicative (ST s) # | Since: base-4.4.0.0 | 
| Functor (ST s) # | Since: base-2.1 | 
| Monad (ST s) # | Since: base-2.1 | 
| Monoid a => Monoid (ST s a) # | Since: base-4.11.0.0 | 
| Semigroup a => Semigroup (ST s a) # | Since: base-4.11.0.0 | 
| Show (ST s a) # | Since: base-2.1 | 
runST :: (forall s. ST s a) -> a #
Return the value computed by a state thread.
 The forall ensures that the internal state used by the ST
 computation is inaccessible to the rest of the program.
Converting ST to IO
RealWorld is deeply magical.  It is primitive, but it is not
         unlifted (hence ptrArg).  We never manipulate values of type
         RealWorld; it's only used in the type system, to parameterise State#.