|Copyright||(c) The University of Glasgow 2001|
|License||BSD-style (see the file libraries/base/LICENSE)|
|Portability||non-portable (requires universal quantification for runST)|
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.
References (variables) that can be used within the
ST monad are provided by Data.STRef, and arrays are provided by Data.Array.ST.
ST monad. The
ST monad allows for destructive updates, but is escapable (unlike IO). A computation of type
ST s a returns a value of type
a, and execute in "thread"
s parameter is either
RealWorld(inside invocations of
It serves to keep the internal states of different invocations of
runST separate from each other and from invocations of
>> operations are strict in the state (though not in values stored in the state). For example,
runST (writeSTRef _|_ v >>= f) = _|_
|Monad (ST s)||
|Functor (ST s)||
|MonadFix (ST s)||
Defined in Control.Monad.Fix
|MonadFail (ST s)||
|Applicative (ST s)||
|Show (ST s a)||
|Semigroup a => Semigroup (ST s a)||
|Monoid a => Monoid (ST s a)||
runST :: (forall s. ST s a) -> a Source
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.
fixST :: (a -> ST s a) -> ST s a Source
Allow the result of an
ST computation to be used (lazily) inside the computation.
Note that if
f is strict,
fixST f = _|_.
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
stToIO :: ST RealWorld a -> IO a Source
Embed a strict state thread in an
IO action. 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
© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).