Copyright	(c) The University of Glasgow 2001
License	BSD-style (see the file libraries/base/LICENSE)
Maintainer	libraries@haskell.org
Stability	stable
Portability	non-portable (requires universal quantification for runST)
Safe Haskell	Unsafe
Language	Haskell2010

Control.Monad.ST.Unsafe

Contents

Unsafe operations

Description

This module provides support for strict state threads, as described in the PLDI '94 paper by John Launchbury and Simon Peyton Jones Lazy Functional State Threads.

Unsafe API.

Synopsis

unsafeInterleaveST :: ST s a -> ST s a
unsafeDupableInterleaveST :: ST s a -> ST s a
unsafeIOToST :: IO a -> ST s a
unsafeSTToIO :: ST s a -> IO a

Unsafe operations

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

unsafeIOToST :: IO a -> ST s a Source #

Convert an IO action to an ST action. This relies on IO and ST having the same representation modulo the constraint on the state thread type parameter.

unsafeSTToIO :: ST s a -> IO a Source #

Convert an ST action to an IO action. This relies on IO and ST having the same representation modulo the constraint on the state thread type parameter.

For an example demonstrating why this is unsafe, see https://mail.haskell.org/pipermail/haskell-cafe/2009-April/060719.html