|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.
Safe API Only.
The strict state-transformer monad.
A computation of type
transforms an internal state indexed
ST s a
s, and returns a value of type
s parameter is either
- an uninstantiated type variable (inside invocations of
RealWorld(inside invocations of
It serves to keep the internal states of different invocations
runST separate from each other and from invocations of
runST(writeSTRef _|_ v >>= f) = _|_
Return the value computed by a state transformer computation.
forall ensures that the internal state used by the
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
ptrArg). We never manipulate values of type
RealWorld; it's only used in the type system, to parameterise