|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.
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
runST (writeSTRef _|_ v >>= f) = _|_
|Monad (ST s)||
|Functor (ST s)||
|MonadFix (ST s)||
|MonadFail (ST s)||
|Applicative (ST s)||
|Show (ST s a)||
|Semigroup a => Semigroup (ST s a)||
|Monoid a => Monoid (ST s 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.
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
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).