base-4.7.0.2: Basic libraries

Copyright | (c) The FFI task force 2003
License | BSD-style (see the file libraries/base/LICENSE)
Maintainer | ffi@haskell.org
Stability | provisional
Portability | portable
Safe Haskell | Unsafe
Language | Haskell2010

Foreign.Marshal.Unsafe

Contents

- Unsafe functions

Description

Marshalling support. Unsafe API.

Synopsis

- unsafeLocalState :: IO a -> a

# Unsafe functions

unsafeLocalState :: IO a -> a

Sometimes an external entity is a pure function, except that it passes arguments and/or results via pointers. The function `unsafeLocalState` permits the packaging of such entities as pure functions.

The only IO operations allowed in the IO action passed to `unsafeLocalState` are (a) local allocation (`alloca`, `allocaBytes` and derived operations such as `withArray` and `withCString`), and (b) pointer operations (`Foreign.Storable` and `Foreign.Ptr`) on the pointers to local storage, and (c) foreign functions whose only observable effect is to read and/or write the locally allocated memory. Passing an IO operation that does not obey these rules results in undefined behaviour.

It is expected that this operation will be replaced in a future revision of Haskell.