base-4.8.2.0: Basic libraries

Copyright | (c) The FFI task force 2001
License | BSD-style (see the file libraries/base/LICENSE)
Maintainer | ffi@haskell.org
Stability | provisional
Portability | portable
Safe Haskell | Trustworthy
Language | Haskell2010

Foreign.Marshal.Utils

Contents

- General marshalling utilities
  - Combined allocation and marshalling
  - Marshalling of Boolean values (non-zero corresponds to `True`)
  - Marshalling of Maybe values
  - Marshalling lists of storable objects
  - Haskellish interface to memcpy and memmove
  - Filling up memory area with required values

Description

Utilities for primitive marshaling

Synopsis

- with :: Storable a => a -> (Ptr a -> IO b) -> IO b
- new :: Storable a => a -> IO (Ptr a)
- fromBool :: Num a => Bool -> a
- toBool :: (Eq a, Num a) => a -> Bool
- maybeNew :: (a -> IO (Ptr b)) -> Maybe a -> IO (Ptr b)
- maybeWith :: (a -> (Ptr b -> IO c) -> IO c) -> Maybe a -> (Ptr b -> IO c) -> IO c
- maybePeek :: (Ptr a -> IO b) -> Ptr a -> IO (Maybe b)
- withMany :: (a -> (b -> res) -> res) -> [a] -> ([b] -> res) -> res
- copyBytes :: Ptr a -> Ptr a -> Int -> IO ()
- moveBytes :: Ptr a -> Ptr a -> Int -> IO ()
- fillBytes :: Ptr a -> Word8 -> Int -> IO ()

# General marshalling utilities

## Combined allocation and marshalling

with :: Storable a => a -> (Ptr a -> IO b) -> IO b

``with` val f` executes the computation `f`, passing as argument a pointer to a temporarily allocated block of memory into which `val` has been marshalled (the combination of `alloca` and `poke`).

The memory is freed when `f` terminates (either normally or via an exception), so the pointer passed to `f` must not be used after this.

new :: Storable a => a -> IO (Ptr a)

Allocate a block of memory and marshal a value into it (the combination of `malloc` and `poke`). The size of the area allocated is determined by the `sizeOf` method from the instance of `Storable` for the appropriate type.

The memory may be deallocated using `free` or `finalizerFree` when no longer required.

## Marshalling of Boolean values (non-zero corresponds to `True`)

fromBool :: Num a => Bool -> a

Convert a Haskell `Bool` to its numeric representation

toBool :: (Eq a, Num a) => a -> Bool

Convert a Boolean in numeric representation to a Haskell value

## Marshalling of Maybe values

maybeNew :: (a -> IO (Ptr b)) -> Maybe a -> IO (Ptr b)

Allocate storage and marshal a storable value wrapped into a `Maybe`

- the `nullPtr` is used to represent `Nothing`

maybeWith :: (a -> (Ptr b -> IO c) -> IO c) -> Maybe a -> (Ptr b -> IO c) -> IO c

Converts a `withXXX` combinator into one marshalling a value wrapped into a `Maybe`, using `nullPtr` to represent `Nothing`.

maybePeek :: (Ptr a -> IO b) -> Ptr a -> IO (Maybe b)

Convert a peek combinator into a one returning `Nothing` if applied to a `nullPtr`

## Marshalling lists of storable objects

withMany :: (a -> (b -> res) -> res) -> [a] -> ([b] -> res) -> res

Replicates a `withXXX` combinator over a list of objects, yielding a list of marshalled objects

## Haskellish interface to memcpy and memmove

(argument order: destination, source)

copyBytes :: Ptr a -> Ptr a -> Int -> IO ()

Copies the given number of bytes from the second area (source) into the first (destination); the copied areas may not overlap

moveBytes :: Ptr a -> Ptr a -> Int -> IO ()

Copies the given number of bytes from the second area (source) into the first (destination); the copied areas may overlap

## Filling up memory area with required values

fillBytes :: Ptr a -> Word8 -> Int -> IO ()

Fill a given number of bytes in memory area with a byte value.

Since: 4.8.0.0