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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE CPP #-}</span>
<a name="line-2"></a><span class='hs-comment'>{-# LANGUAGE Rank2Types #-}</span>
<a name="line-3"></a><span class='hs-comment'>{-# LANGUAGE FlexibleContexts #-}</span>
<a name="line-4"></a>
<a name="line-5"></a><span class='hs-cpp'>#ifndef MIN_VERSION_base</span>
<a name="line-6"></a><span class='hs-cpp'>#define MIN_VERSION_base(x,y,z) 1</span>
<a name="line-7"></a><span class='hs-cpp'>#endif</span>
<a name="line-8"></a>
<a name="line-9"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-10"></a><span class='hs-comment'>-- |</span>
<a name="line-11"></a><span class='hs-comment'>-- Module : Data.List.Lens</span>
<a name="line-12"></a><span class='hs-comment'>-- Copyright : (C) 2012-16 Edward Kmett</span>
<a name="line-13"></a><span class='hs-comment'>-- License : BSD-style (see the file LICENSE)</span>
<a name="line-14"></a><span class='hs-comment'>-- Maintainer : Edward Kmett <ekmett@gmail.com></span>
<a name="line-15"></a><span class='hs-comment'>-- Stability : provisional</span>
<a name="line-16"></a><span class='hs-comment'>-- Portability : portable</span>
<a name="line-17"></a><span class='hs-comment'>--</span>
<a name="line-18"></a><span class='hs-comment'>-- Traversals for manipulating parts of a list.</span>
<a name="line-19"></a><span class='hs-comment'>--</span>
<a name="line-20"></a><span class='hs-comment'>-- Additional optics for manipulating lists are present more</span>
<a name="line-21"></a><span class='hs-comment'>-- generically in this package.</span>
<a name="line-22"></a><span class='hs-comment'>--</span>
<a name="line-23"></a><span class='hs-comment'>-- The 'Control.Lens.At.Ixed' class allows traversing the element at a</span>
<a name="line-24"></a><span class='hs-comment'>-- specific list index.</span>
<a name="line-25"></a><span class='hs-comment'>--</span>
<a name="line-26"></a><span class='hs-comment'>-- >>> [0..10] ^? ix 4</span>
<a name="line-27"></a><span class='hs-comment'>-- Just 4</span>
<a name="line-28"></a><span class='hs-comment'>--</span>
<a name="line-29"></a><span class='hs-comment'>-- >>> [0..5] & ix 4 .~ 2</span>
<a name="line-30"></a><span class='hs-comment'>-- [0,1,2,3,2,5]</span>
<a name="line-31"></a><span class='hs-comment'>--</span>
<a name="line-32"></a><span class='hs-comment'>-- >>> [0..10] ^? ix 14</span>
<a name="line-33"></a><span class='hs-comment'>-- Nothing</span>
<a name="line-34"></a><span class='hs-comment'>--</span>
<a name="line-35"></a><span class='hs-comment'>-- >>> [0..5] & ix 14 .~ 2</span>
<a name="line-36"></a><span class='hs-comment'>-- [0,1,2,3,4,5]</span>
<a name="line-37"></a><span class='hs-comment'>--</span>
<a name="line-38"></a><span class='hs-comment'>-- The 'Control.Lens.Cons.Cons' and 'Control.Lens.Empty.AsEmpty'</span>
<a name="line-39"></a><span class='hs-comment'>-- classes provide 'Control.Lens.Prism.Prism's for list constructors.</span>
<a name="line-40"></a><span class='hs-comment'>--</span>
<a name="line-41"></a><span class='hs-comment'>-- >>> [1..10] ^? _Cons</span>
<a name="line-42"></a><span class='hs-comment'>-- Just (1,[2,3,4,5,6,7,8,9,10])</span>
<a name="line-43"></a><span class='hs-comment'>--</span>
<a name="line-44"></a><span class='hs-comment'>-- >>> [] ^? _Cons</span>
<a name="line-45"></a><span class='hs-comment'>-- Nothing</span>
<a name="line-46"></a><span class='hs-comment'>--</span>
<a name="line-47"></a><span class='hs-comment'>-- >>> [] ^? _Empty</span>
<a name="line-48"></a><span class='hs-comment'>-- Just ()</span>
<a name="line-49"></a><span class='hs-comment'>--</span>
<a name="line-50"></a><span class='hs-comment'>-- >>> _Cons # (1, _Empty # ()) :: [Int]</span>
<a name="line-51"></a><span class='hs-comment'>-- [1]</span>
<a name="line-52"></a><span class='hs-comment'>--</span>
<a name="line-53"></a><span class='hs-comment'>-- Additionally, 'Control.Lens.Cons.Snoc' provides a</span>
<a name="line-54"></a><span class='hs-comment'>-- 'Control.Lens.Prism.Prism' for accessing the end of a list. Note</span>
<a name="line-55"></a><span class='hs-comment'>-- that this 'Control.Lens.Prism.Prism' always will need to traverse</span>
<a name="line-56"></a><span class='hs-comment'>-- the whole list.</span>
<a name="line-57"></a><span class='hs-comment'>--</span>
<a name="line-58"></a><span class='hs-comment'>-- >>> [1..5] ^? _Snoc</span>
<a name="line-59"></a><span class='hs-comment'>-- Just ([1,2,3,4],5)</span>
<a name="line-60"></a><span class='hs-comment'>--</span>
<a name="line-61"></a><span class='hs-comment'>-- >>> _Snoc # ([1,2],5)</span>
<a name="line-62"></a><span class='hs-comment'>-- [1,2,5]</span>
<a name="line-63"></a><span class='hs-comment'>--</span>
<a name="line-64"></a><span class='hs-comment'>-- An instance of 'Control.Lens.Plated.Plated' allows for finding</span>
<a name="line-65"></a><span class='hs-comment'>-- locations in the list where a traversal matches.</span>
<a name="line-66"></a><span class='hs-comment'>--</span>
<a name="line-67"></a><span class='hs-comment'>-- >>> [Nothing, Just 7, Just 3, Nothing] & deep (ix 0 . _Just) +~ 10</span>
<a name="line-68"></a><span class='hs-comment'>-- [Nothing,Just 17,Just 3,Nothing]</span>
<a name="line-69"></a><span class='hs-comment'>--</span>
<a name="line-70"></a><span class='hs-comment'>-- An instance of 'Control.Lens.Iso.Reversing' provides an</span>
<a name="line-71"></a><span class='hs-comment'>-- 'Control.Lens.Iso.Iso' between a list and its reverse.</span>
<a name="line-72"></a><span class='hs-comment'>--</span>
<a name="line-73"></a><span class='hs-comment'>-- >>> "live" & reversed %~ ('d':)</span>
<a name="line-74"></a><span class='hs-comment'>-- "lived"</span>
<a name="line-75"></a><span class='hs-comment'>--</span>
<a name="line-76"></a><span class='hs-comment'>-- Finally, it's possible to traverse, fold over, and map over</span>
<a name="line-77"></a><span class='hs-comment'>-- index-value pairs thanks to instances of</span>
<a name="line-78"></a><span class='hs-comment'>-- 'Control.Lens.Indexed.TraversableWithIndex',</span>
<a name="line-79"></a><span class='hs-comment'>-- 'Control.Lens.Indexed.FoldableWithIndex', and</span>
<a name="line-80"></a><span class='hs-comment'>-- 'Control.Lens.Indexed.FunctorWithIndex'.</span>
<a name="line-81"></a><span class='hs-comment'>--</span>
<a name="line-82"></a><span class='hs-comment'>-- >>> imap (,) "Hello"</span>
<a name="line-83"></a><span class='hs-comment'>-- [(0,'H'),(1,'e'),(2,'l'),(3,'l'),(4,'o')]</span>
<a name="line-84"></a><span class='hs-comment'>--</span>
<a name="line-85"></a><span class='hs-comment'>-- >>> ifoldMap replicate "Hello"</span>
<a name="line-86"></a><span class='hs-comment'>-- "ellllloooo"</span>
<a name="line-87"></a><span class='hs-comment'>--</span>
<a name="line-88"></a><span class='hs-comment'>-- >>> itraverse_ (curry print) "Hello"</span>
<a name="line-89"></a><span class='hs-comment'>-- (0,'H')</span>
<a name="line-90"></a><span class='hs-comment'>-- (1,'e')</span>
<a name="line-91"></a><span class='hs-comment'>-- (2,'l')</span>
<a name="line-92"></a><span class='hs-comment'>-- (3,'l')</span>
<a name="line-93"></a><span class='hs-comment'>-- (4,'o')</span>
<a name="line-94"></a><span class='hs-comment'>--</span>
<a name="line-95"></a><span class='hs-comment'>----------------------------------------------------------------------------</span>
<a name="line-96"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>List</span><span class='hs-varop'>.</span><span class='hs-conid'>Lens</span>
<a name="line-97"></a> <span class='hs-layout'>(</span> <span class='hs-varid'>prefixed</span>
<a name="line-98"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>suffixed</span>
<a name="line-99"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>stripSuffix</span>
<a name="line-100"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-101"></a>
<a name="line-102"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span> <span class='hs-layout'>(</span><span class='hs-varid'>guard</span><span class='hs-layout'>)</span>
<a name="line-103"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Lens</span>
<a name="line-104"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>List</span>
<a name="line-105"></a>
<a name="line-106"></a><span class='hs-cpp'>#if !MIN_VERSION_base(4,8,0)</span>
<a name="line-107"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Functor</span>
<a name="line-108"></a><span class='hs-cpp'>#endif</span>
<a name="line-109"></a>
<a name="line-110"></a><span class='hs-comment'>-- $setup</span>
<a name="line-111"></a><span class='hs-comment'>-- >>> :set -XNoOverloadedStrings</span>
<a name="line-112"></a><span class='hs-comment'>-- >>> import Debug.SimpleReflect.Expr</span>
<a name="line-113"></a><span class='hs-comment'>-- >>> import Debug.SimpleReflect.Vars as Vars hiding (f,g)</span>
<a name="line-114"></a><span class='hs-comment'>-- >>> let f :: Expr -> Expr; f = Debug.SimpleReflect.Vars.f</span>
<a name="line-115"></a><span class='hs-comment'>-- >>> let g :: Expr -> Expr; g = Debug.SimpleReflect.Vars.g</span>
<a name="line-116"></a>
<a name="line-117"></a><a name="prefixed"></a><span class='hs-comment'>-- | A 'Prism' stripping a prefix from a list when used as a 'Traversal', or</span>
<a name="line-118"></a><span class='hs-comment'>-- prepending that prefix when run backwards:</span>
<a name="line-119"></a><span class='hs-comment'>--</span>
<a name="line-120"></a><span class='hs-comment'>-- >>> "preview" ^? prefixed "pre"</span>
<a name="line-121"></a><span class='hs-comment'>-- Just "view"</span>
<a name="line-122"></a><span class='hs-comment'>--</span>
<a name="line-123"></a><span class='hs-comment'>-- >>> "review" ^? prefixed "pre"</span>
<a name="line-124"></a><span class='hs-comment'>-- Nothing</span>
<a name="line-125"></a><span class='hs-comment'>--</span>
<a name="line-126"></a><span class='hs-comment'>-- >>> prefixed "pre" # "amble"</span>
<a name="line-127"></a><span class='hs-comment'>-- "preamble"</span>
<a name="line-128"></a><span class='hs-definition'>prefixed</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Eq</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Prism'</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span>
<a name="line-129"></a><span class='hs-definition'>prefixed</span> <span class='hs-varid'>ps</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>prism'</span> <span class='hs-layout'>(</span><span class='hs-varid'>ps</span> <span class='hs-varop'>++</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>stripPrefix</span> <span class='hs-varid'>ps</span><span class='hs-layout'>)</span>
<a name="line-130"></a><span class='hs-comment'>{-# INLINE prefixed #-}</span>
<a name="line-131"></a>
<a name="line-132"></a><a name="suffixed"></a><span class='hs-comment'>-- | A 'Prism' stripping a suffix from a list when used as a 'Traversal', or</span>
<a name="line-133"></a><span class='hs-comment'>-- appending that suffix when run backwards:</span>
<a name="line-134"></a><span class='hs-comment'>--</span>
<a name="line-135"></a><span class='hs-comment'>-- >>> "review" ^? suffixed "view"</span>
<a name="line-136"></a><span class='hs-comment'>-- Just "re"</span>
<a name="line-137"></a><span class='hs-comment'>--</span>
<a name="line-138"></a><span class='hs-comment'>-- >>> "review" ^? suffixed "tire"</span>
<a name="line-139"></a><span class='hs-comment'>-- Nothing</span>
<a name="line-140"></a><span class='hs-comment'>--</span>
<a name="line-141"></a><span class='hs-comment'>-- >>> suffixed ".o" # "hello"</span>
<a name="line-142"></a><span class='hs-comment'>-- "hello.o"</span>
<a name="line-143"></a><span class='hs-definition'>suffixed</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Eq</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Prism'</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span>
<a name="line-144"></a><span class='hs-definition'>suffixed</span> <span class='hs-varid'>qs</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>prism'</span> <span class='hs-layout'>(</span><span class='hs-varop'>++</span> <span class='hs-varid'>qs</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>stripSuffix</span> <span class='hs-varid'>qs</span><span class='hs-layout'>)</span>
<a name="line-145"></a><span class='hs-comment'>{-# INLINE suffixed #-}</span>
<a name="line-146"></a>
<a name="line-147"></a><span class='hs-comment'>------------------------------------------------------------------------------</span>
<a name="line-148"></a><span class='hs-comment'>-- Util</span>
<a name="line-149"></a><span class='hs-comment'>------------------------------------------------------------------------------</span>
<a name="line-150"></a>
<a name="line-151"></a><a name="stripSuffix"></a><span class='hs-definition'>stripSuffix</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Eq</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Maybe</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span>
<a name="line-152"></a><span class='hs-definition'>stripSuffix</span> <span class='hs-varid'>qs</span> <span class='hs-varid'>xs0</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>go</span> <span class='hs-varid'>xs0</span> <span class='hs-varid'>zs</span>
<a name="line-153"></a> <span class='hs-keyword'>where</span>
<a name="line-154"></a> <span class='hs-varid'>zs</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>drp</span> <span class='hs-varid'>qs</span> <span class='hs-varid'>xs0</span>
<a name="line-155"></a> <span class='hs-varid'>drp</span> <span class='hs-layout'>(</span><span class='hs-keyword'>_</span><span class='hs-conop'>:</span><span class='hs-varid'>ps</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-keyword'>_</span><span class='hs-conop'>:</span><span class='hs-varid'>xs</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>drp</span> <span class='hs-varid'>ps</span> <span class='hs-varid'>xs</span>
<a name="line-156"></a> <span class='hs-varid'>drp</span> <span class='hs-conid'>[]</span> <span class='hs-varid'>xs</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>xs</span>
<a name="line-157"></a> <span class='hs-varid'>drp</span> <span class='hs-keyword'>_</span> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>[]</span>
<a name="line-158"></a> <span class='hs-varid'>go</span> <span class='hs-layout'>(</span><span class='hs-keyword'>_</span><span class='hs-conop'>:</span><span class='hs-varid'>xs</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-keyword'>_</span><span class='hs-conop'>:</span><span class='hs-varid'>ys</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>go</span> <span class='hs-varid'>xs</span> <span class='hs-varid'>ys</span>
<a name="line-159"></a> <span class='hs-varid'>go</span> <span class='hs-varid'>xs</span> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>zipWith</span> <span class='hs-varid'>const</span> <span class='hs-varid'>xs0</span> <span class='hs-varid'>zs</span> <span class='hs-varop'><$</span> <span class='hs-varid'>guard</span> <span class='hs-layout'>(</span><span class='hs-varid'>xs</span> <span class='hs-varop'>==</span> <span class='hs-varid'>qs</span><span class='hs-layout'>)</span>
<a name="line-160"></a> <span class='hs-varid'>go</span> <span class='hs-conid'>[]</span> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>Nothing</span> <span class='hs-comment'>-- impossible</span>
<a name="line-161"></a><span class='hs-comment'>{-# INLINE stripSuffix #-}</span>
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