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Data.Array.MArray

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

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
newArray :: (MArray a e m, Ix i) => (i, i) -> e -> m (a i e)
newArray_ :: (MArray a e m, Ix i) => (i, i) -> m (a i e)
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)
getBounds :: (MArray a e m, Ix i) => a i e -> m (i, i)
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 undefined.

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

The `Ix` class and operations
module Data.Ix
Constructing mutable arrays
newArray :: (MArray a e m, Ix i) => (i, i) -> e -> m (a i e)
Builds a new array, with every element initialised to the supplied value.
newArray_ :: (MArray a e m, Ix i) => (i, i) -> m (a i e)
Builds a new array, with every element initialised to undefined.
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
getBounds :: (MArray a e m, Ix i) => a i e -> m (i, i)
Returns the bounds of the array
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.

- `IOUArray` -> `UArray`
- `STUArray` -> `UArray`
- `IOArray` -> `Array`
- `STArray` -> `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.

- `UArray` -> `IOUArray`
- `UArray` -> `STUArray`
- `Array` -> `IOArray`
- `Array` -> `STArray`

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