Copyright	(c) The University of Glasgow 1992-2002
License	see libraries/base/LICENSE
Maintainer	[email protected]
Stability	internal
Portability	non-portable (GHC Extensions)
Safe Haskell	Unsafe
Language	Haskell2010

newtype ST s a Source

The strict 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. 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 strict in the state (though not in values stored in the state). For example,

runST (writeSTRef _|_ v >>= f) = _|_

data STret s a Source

type STRep s a = State# s -> (# State# s, a #) Source

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.

Unsafe functions

liftST :: ST s a -> State# s -> STret s a Source

unsafeInterleaveST :: ST s a -> ST s a Source

unsafeInterleaveST allows an ST computation to be deferred lazily. When passed a value of type ST a, the ST computation will only be performed when the value of the a is demanded.

unsafeDupableInterleaveST :: ST s a -> ST s a Source

unsafeDupableInterleaveST allows an ST computation to be deferred lazily. When passed a value of type ST a, the ST computation will only be performed when the value of the a is demanded.

The computation may be performed multiple times by different threads, possibly at the same time. To prevent this, use unsafeInterleaveST instead.

Since: base-4.11