| 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) | 
| Safe Haskell | Trustworthy | 
| Language | Haskell2010 | 
Control.Monad.ST.Lazy
Description
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.
The ST monad
The lazy STIO).
 A computation of type ST s aa, and
 executes 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 not strict in the state.  For example,
runST (writeSTRef _|_ v >>= readSTRef _|_ >> return 2) = 2Converting between strict and lazy ST
strictToLazyST :: ST s a -> ST s a #
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.
lazyToStrictST :: ST s a -> ST s a #
Convert a lazy ST computation into a strict one.
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#.