Portability | non-portable (uses Data.Array.Base) |
---|---|

Stability | experimental |

Maintainer | libraries@haskell.org |

Safe Haskell | Safe-Infered |

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.

- class Monad m => MArray a e m where
- 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 whereSource

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.

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

Returns the bounds of the array

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

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

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

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.

# 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)Source

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

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

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)Source

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)Source

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]Source

Return a list of all the elements of a mutable array

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

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

# Conversions between mutable and immutable arrays

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

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.

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

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 unsafeThaw*write*unsafeFreeze
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.