array-0.3.0.2: Mutable and immutable arrays

Portability | non-portable (uses Data.Array.Base)
Stability | experimental
Maintainer | libraries@haskell.org

Data.Array.MArray

Contents

- Class of mutable array types
- The `Ix` class and operations
- Constructing mutable arrays
- Reading and writing mutable arrays
- Derived arrays
- Deconstructing mutable arrays
- Conversions between mutable and immutable arrays

Description

An overloaded interface to mutable arrays. For array types which can be used with this interface, see Data.Array.IO, Data.Array.ST, and Data.Array.Storable.

Synopsis

- class Monad m => MArray a e m where
  - getBounds :: Ix i => a i e -> m (i, i)
  - newArray :: Ix i => (i, i) -> e -> m (a i e)
  - newArray_ :: Ix i => (i, i) -> m (a i e)
- module Data.Ix
- newListArray :: (MArray a e m, Ix i) => (i, i) -> [e] -> m (a i e)
- readArray :: (MArray a e m, Ix i) => a i e -> i -> m e
- writeArray :: (MArray a e m, Ix i) => a i e -> i -> e -> m ()
- mapArray :: (MArray a e' m, MArray a e m, Ix i) => (e' -> e) -> a i e' -> m (a i e)
- mapIndices :: (MArray a e m, Ix i, Ix j) => (i, i) -> (i -> j) -> a j e -> m (a i e)
- getElems :: (MArray a e m, Ix i) => a i e -> m [e]
- getAssocs :: (MArray a e m, Ix i) => a i e -> m [(i, e)]
- freeze :: (Ix i, MArray a e m, IArray b e) => a i e -> m (b i e)
- unsafeFreeze :: (Ix i, MArray a e m, IArray b e) => a i e -> m (b i e)
- thaw :: (Ix i, IArray a e, MArray b e m) => a i e -> m (b i e)
- unsafeThaw :: (Ix i, IArray a e, MArray b e m) => a i e -> m (b i e)

# Class of mutable array types

class Monad m => MArray a e m where

Class of mutable array types.

An array type has the form `(a i e)` where `a` is the array type constructor (kind `* -> * -> *`), `i` is the index type (a member of the class `Ix`), and `e` is the element type.

The `MArray` class is parameterised over both `a` and `e` (so that instances specialised to certain element types can be defined, in the same way as for `IArray`), and also over the type of the monad, `m`, in which the mutable array will be manipulated.

Methods

getBounds :: Ix i => a i e -> m (i, i)

Returns the bounds of the array

newArray :: Ix i => (i, i) -> e -> m (a i e)

Builds a new array, with every element initialised to the supplied value.

newArray_ :: Ix i => (i, i) -> m (a i e)

Builds a new array, with every element initialised to an undefined value. In a monadic context in which operations must be deterministic (e.g. the ST monad), the array elements are initialised to a fixed but undefined value, such as zero.

Instances

MArray IOArray e IO |
MArray IOUArray Bool IO |
MArray IOUArray Char IO |
MArray IOUArray Double IO |
MArray IOUArray Float IO |
MArray IOUArray Int IO |
MArray IOUArray Int8 IO |
MArray IOUArray Int16 IO |
MArray IOUArray Int32 IO |
MArray IOUArray Int64 IO |
MArray IOUArray Word IO |
MArray IOUArray Word8 IO |
MArray IOUArray Word16 IO |
MArray IOUArray Word32 IO |
MArray IOUArray Word64 IO |
Storable e => MArray StorableArray e IO |
MArray IOUArray (StablePtr a) IO |
MArray IOUArray (Ptr a) IO |
MArray IOUArray (FunPtr a) IO |
MArray (STArray s) e (ST s) |
MArray (STArray s) e (ST s) |
MArray (STUArray s) Word64 (ST s) |
MArray (STUArray s) Word32 (ST s) |
MArray (STUArray s) Word16 (ST s) |
MArray (STUArray s) Word8 (ST s) |
MArray (STUArray s) Int64 (ST s) |
MArray (STUArray s) Int32 (ST s) |
MArray (STUArray s) Int16 (ST s) |
MArray (STUArray s) Int8 (ST s) |
MArray (STUArray s) Double (ST s) |
MArray (STUArray s) Float (ST s) |
MArray (STUArray s) Word (ST s) |
MArray (STUArray s) Int (ST s) |
MArray (STUArray s) Char (ST s) |
MArray (STUArray s) Bool (ST s) |
MArray (STUArray s) (StablePtr a) (ST s) |
MArray (STUArray s) (FunPtr a) (ST s) |
MArray (STUArray s) (Ptr a) (ST s) |

# The `Ix` class and operations

module Data.Ix

# Constructing mutable arrays

newListArray :: (MArray a e m, Ix i) => (i, i) -> [e] -> m (a i e)

Constructs a mutable array from a list of initial elements. The list gives the elements of the array in ascending order beginning with the lowest index.

# Reading and writing mutable arrays

readArray :: (MArray a e m, Ix i) => a i e -> i -> m e

Read an element from a mutable array

writeArray :: (MArray a e m, Ix i) => a i e -> i -> e -> m ()

Write an element in a mutable array

# Derived arrays

mapArray :: (MArray a e' m, MArray a e m, Ix i) => (e' -> e) -> a i e' -> m (a i e)

Constructs a new array derived from the original array by applying a function to each of the elements.

mapIndices :: (MArray a e m, Ix i, Ix j) => (i, i) -> (i -> j) -> a j e -> m (a i e)

Constructs a new array derived from the original array by applying a function to each of the indices.

# Deconstructing mutable arrays

getElems :: (MArray a e m, Ix i) => a i e -> m [e]

Return a list of all the elements of a mutable array

getAssocs :: (MArray a e m, Ix i) => a i e -> m [(i, e)]

Return a list of all the associations of a mutable array, in index order.

# Conversions between mutable and immutable arrays

freeze :: (Ix i, MArray a e m, IArray b e) => a i e -> m (b i e)

Converts a mutable array (any instance of `MArray`) to an immutable array (any instance of `IArray`) by taking a complete copy of it.

unsafeFreeze :: (Ix i, MArray a e m, IArray b e) => a i e -> m (b i e)

Converts an mutable array into an immutable array. The implementation may either simply cast the array from one type to the other without copying the array, or it may take a full copy of the array.

Note that because the array is possibly not copied, any subsequent modifications made to the mutable version of the array may be shared with the immutable version. It is safe to use, therefore, if the mutable version is never modified after the freeze operation.

The non-copying implementation is supported between certain pairs of array types only; one constraint is that the array types must have identical representations. In GHC, The following pairs of array types have a non-copying O(1) implementation of `unsafeFreeze`. Because the optimised versions are enabled by specialisations, you will need to compile with optimisation (-O) to get them.

- `Data.Array.IO.IOUArray` -> `Data.Array.Unboxed.UArray`
- `Data.Array.ST.STUArray` -> `Data.Array.Unboxed.UArray`
- `Data.Array.IO.IOArray` -> `Data.Array.Array`
- `Data.Array.ST.STArray` -> `Data.Array.Array`

thaw :: (Ix i, IArray a e, MArray b e m) => a i e -> m (b i e)

Converts an immutable array (any instance of `IArray`) into a mutable array (any instance of `MArray`) by taking a complete copy of it.

unsafeThaw :: (Ix i, IArray a e, MArray b e m) => a i e -> m (b i e)

Converts an immutable array into a mutable array. The implementation may either simply cast the array from one type to the other without copying the array, or it may take a full copy of the array.

Note that because the array is possibly not copied, any subsequent modifications made to the mutable version of the array may be shared with the immutable version. It is only safe to use, therefore, if the immutable array is never referenced again in this thread, and there is no possibility that it can be also referenced in another thread. If you use an unsafeThawwriteunsafeFreeze sequence in a multi-threaded setting, then you must ensure that this sequence is atomic with respect to other threads, or a garbage collector crash may result (because the write may be writing to a frozen array).

The non-copying implementation is supported between certain pairs of array types only; one constraint is that the array types must have identical representations. In GHC, The following pairs of array types have a non-copying O(1) implementation of `unsafeThaw`. Because the optimised versions are enabled by specialisations, you will need to compile with optimisation (-O) to get them.

- `Data.Array.Unboxed.UArray` -> `Data.Array.IO.IOUArray`
- `Data.Array.Unboxed.UArray` -> `Data.Array.ST.STUArray`
- `Data.Array.Array` -> `Data.Array.IO.IOArray`
- `Data.Array.Array` -> `Data.Array.ST.STArray`