|Copyright||(c) The University of Glasgow 2001|
|License||BSD-style (see the file libraries/base/LICENSE)|
|Portability||non-portable (requires universal quantification for runST)|
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 strict state-transformer monad. A computation of type
ST s a transforms an internal state indexed by
s, and returns a value of type
s parameter is either
RealWorld(inside invocations of
runST(writeSTRef _|_ v >>= f) = _|_
Return the value computed by a state transformer computation. The
forall ensures that the internal state used by the
ST computation is inaccessible to the rest of the program.
Allow the result of a state transformer 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
A monad transformer embedding strict 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
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Licensed under a BSD-style license (see top of the page).