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streamly/core/src/Streamly/Data/Array.hs
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1{-# LANGUAGE CPP #-}
2-- |
3-- Module : Streamly.Data.Array
4-- Copyright : (c) 2019 Composewell Technologies
5--
6-- License : BSD3
7-- Maintainer : streamly@composewell.com
8-- Stability : released
9-- Portability : GHC
10--
11-- Unboxed immutable arrays with streaming interfaces.
12--
13-- Please refer to "Streamly.Internal.Data.Array" for functions that have not
14-- yet been released.
15--
16-- For arrays that work on boxed types, not requiring the 'Unbox' constraint,
17-- please refer to "Streamly.Data.Array.Generic". For arrays that can be
18-- mutated in-place, please see "Streamly.Data.MutArray".
20module Streamly.Data.Array
21 (
22 -- * Setup
23 -- | To execute the code examples provided in this module in ghci, please
24 -- run the following commands first.
25 --
26 -- $setup
28 -- * Overview
29 -- $overview
31 -- * The Array Type
32 Array
34 -- * Construction
35 -- | When performance matters, the fastest way to generate an array is
36 -- 'writeN'. 'IsList' and 'IsString' instances can be
37 -- used to conveniently construct arrays from literal values.
38 -- 'OverloadedLists' extension or 'fromList' can be used to construct an
39 -- array from a list literal. Similarly, 'OverloadedStrings' extension or
40 -- 'fromList' can be used to construct an array from a string literal.
42 -- Pure List APIs
43 , fromListN
44 , fromList
46 -- Monadic APIs
47 , writeN -- drop new
48 , write -- full buffer
49 , writeLastN -- drop old (ring buffer)
51 -- * Conversion
52 -- 'GHC.Exts.toList' from "GHC.Exts" can be used to convert an array to a
53 -- list.
54 , toList
56 -- * Pinning & Unpinning
57 -- | Arrays are created unpinned by default unless pinned versions of
58 -- creation APIs are used. Look for APIs with @pinned@ prefix in
59 -- "Streamly.Internal.Data.Array" for some unreleased pinned creation APIs.
60 -- If an array is to be sent to the OS without any further modification
61 -- then it should be created pinned in the first place instead of pinning
62 -- it later. Pinning an unpinned array has a copy overhead. OS interfacing
63 -- APIs create a pinned array directly or convert an unpinned array to
64 -- pinned array before sending it to the OS.
65 , pin
66 , unpin
67 , isPinned
69 -- * Streams
70 , read
71 , readRev
73 -- * Unfolds
74 , reader
75 , readerRev
77 -- * Casting
78 , cast
79 , asBytes
81 -- * Random Access
82 , length
83 -- , (!!)
84 , getIndex
86 -- * Re-exports
87 , Unbox (..)
89 )
90where
92#include "inline.hs"
94import Streamly.Internal.Data.Array
95import Streamly.Internal.Data.Unbox (Unbox (..))
97import Prelude hiding (read, length)
99#include "DocTestDataArray.hs"
101-- $overview
102--
103-- This module provides APIs to create and use unboxed immutable arrays. Once
104-- created, their contents cannot be modified. Only types that are unboxable
105-- via the 'Unbox' type class can be stored in these arrays. Note that the
106-- array memory grows automatically when creating a new array, therefore, an
107-- array can be created from a variable length stream.
108--
109-- == Folding Arrays
110--
111-- Convert array to stream, and fold the stream:
112--
113-- >>> fold f arr = Array.read arr & Stream.fold f
114-- >>> fold Fold.sum (Array.fromList [1,2,3::Int])
115-- 6
116--
117-- == Transforming Arrays
118--
119-- Convert array to stream, transform, and fold back to array:
120--
121-- >>> amap f arr = Array.read arr & fmap f & Stream.fold Array.write
122-- >>> amap (+1) (Array.fromList [1,2,3::Int])
123-- fromList [2,3,4]
124--
125-- == Pinned and Unpinned Arrays
126--
127-- The array type can use both pinned and unpinned memory under the hood. The
128-- default array creation operations create unpinned arrays. IO operations
129-- automatically copy an array to pinned memory if the array passed to it is
130-- unpinned. Programmers can use appropriate pinned array generation APIs to
131-- reduce the copying if it happens.
132--
133-- Unpinned arrays have the advantage of allowing automatic defragmentation of
134-- the memory by GC. Whereas pinned arrays have the advantage of not requiring
135-- a copy by GC. Normally you would want to use unpinned arrays. However, in
136-- some cases, for example, for long lived large data storage, and for
137-- interfacing with the operating system or foreign (non-Haskell) consumers you
138-- may want to use pinned arrays.
139--
140-- == Creating Arrays from Non-IO Streams
141--
142-- Array creation folds require 'MonadIO' otherwise the compiler may
143-- incorrectly share the array memory thinking it is pure.
144--
145-- See the 'fromPureStream' unreleased API to generate an array from an
146-- Identity stream safely without using MonadIO constraint.
147--
148--
149-- Note that 'Identity' streams can be generalized to IO streams:
150--
151-- >>> pure = Stream.fromList [1,2,3] :: Stream Identity Int
152-- >>> generally = Stream.morphInner (return . runIdentity)
153-- >>> Stream.fold Array.write (generally pure :: Stream IO Int)
154-- fromList [1,2,3]
155--
156-- == Programming Tips
157--
158-- This module is designed to be imported qualified:
159--
160-- >>> import qualified Streamly.Data.Array as Array