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<title>XMonad/Util/ExtensibleState.hs</title>
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<pre><a name="line-1"></a><span class='hs-comment'>{-# LANGUAGE PatternGuards #-}</span>
<a name="line-2"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-3"></a><span class='hs-comment'>-- |</span>
<a name="line-4"></a><span class='hs-comment'>-- Module : XMonad.Util.ExtensibleState</span>
<a name="line-5"></a><span class='hs-comment'>-- Copyright : (c) Daniel Schoepe 2009</span>
<a name="line-6"></a><span class='hs-comment'>-- License : BSD3-style (see LICENSE)</span>
<a name="line-7"></a><span class='hs-comment'>--</span>
<a name="line-8"></a><span class='hs-comment'>-- Maintainer : daniel.schoepe@gmail.com</span>
<a name="line-9"></a><span class='hs-comment'>-- Stability : unstable</span>
<a name="line-10"></a><span class='hs-comment'>-- Portability : not portable</span>
<a name="line-11"></a><span class='hs-comment'>--</span>
<a name="line-12"></a><span class='hs-comment'>-- Module for storing custom mutable state in xmonad.</span>
<a name="line-13"></a><span class='hs-comment'>--</span>
<a name="line-14"></a><span class='hs-comment'>-----------------------------------------------------------------------------</span>
<a name="line-15"></a>
<a name="line-16"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>XMonad</span><span class='hs-varop'>.</span><span class='hs-conid'>Util</span><span class='hs-varop'>.</span><span class='hs-conid'>ExtensibleState</span> <span class='hs-layout'>(</span>
<a name="line-17"></a> <span class='hs-comment'>-- * Usage</span>
<a name="line-18"></a> <span class='hs-comment'>-- $usage</span>
<a name="line-19"></a> <span class='hs-varid'>put</span>
<a name="line-20"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>modify</span>
<a name="line-21"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>remove</span>
<a name="line-22"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>get</span>
<a name="line-23"></a> <span class='hs-layout'>,</span> <span class='hs-varid'>gets</span>
<a name="line-24"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-25"></a>
<a name="line-26"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Typeable</span> <span class='hs-layout'>(</span><span class='hs-varid'>typeOf</span><span class='hs-layout'>,</span><span class='hs-conid'>Typeable</span><span class='hs-layout'>,</span><span class='hs-varid'>cast</span><span class='hs-layout'>)</span>
<a name="line-27"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Map</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>M</span>
<a name="line-28"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>XMonad</span><span class='hs-varop'>.</span><span class='hs-conid'>Core</span>
<a name="line-29"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>State</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>State</span>
<a name="line-30"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Maybe</span> <span class='hs-layout'>(</span><span class='hs-varid'>fromMaybe</span><span class='hs-layout'>)</span>
<a name="line-31"></a>
<a name="line-32"></a><span class='hs-comment'>-- ---------------------------------------------------------------------</span>
<a name="line-33"></a><span class='hs-comment'>-- $usage</span>
<a name="line-34"></a><span class='hs-comment'>--</span>
<a name="line-35"></a><span class='hs-comment'>-- To utilize this feature in a contrib module, create a data type</span>
<a name="line-36"></a><span class='hs-comment'>-- and make it an instance of ExtensionClass. You can then use</span>
<a name="line-37"></a><span class='hs-comment'>-- the functions from this module for storing and retrieving your data:</span>
<a name="line-38"></a><span class='hs-comment'>--</span>
<a name="line-39"></a><span class='hs-comment'>-- > {-# LANGUAGE DeriveDataTypeable #-}</span>
<a name="line-40"></a><span class='hs-comment'>-- > import qualified XMonad.Util.ExtensibleState as XS</span>
<a name="line-41"></a><span class='hs-comment'>-- ></span>
<a name="line-42"></a><span class='hs-comment'>-- > data ListStorage = ListStorage [Integer] deriving Typeable</span>
<a name="line-43"></a><span class='hs-comment'>-- > instance ExtensionClass ListStorage where</span>
<a name="line-44"></a><span class='hs-comment'>-- > initialValue = ListStorage []</span>
<a name="line-45"></a><span class='hs-comment'>-- ></span>
<a name="line-46"></a><span class='hs-comment'>-- > .. XS.put (ListStorage [23,42])</span>
<a name="line-47"></a><span class='hs-comment'>--</span>
<a name="line-48"></a><span class='hs-comment'>-- To retrieve the stored value call:</span>
<a name="line-49"></a><span class='hs-comment'>--</span>
<a name="line-50"></a><span class='hs-comment'>-- > .. XS.get</span>
<a name="line-51"></a><span class='hs-comment'>--</span>
<a name="line-52"></a><span class='hs-comment'>-- If the type can't be inferred from the usage of the retrieved data, you</span>
<a name="line-53"></a><span class='hs-comment'>-- have to add an explicit type signature:</span>
<a name="line-54"></a><span class='hs-comment'>--</span>
<a name="line-55"></a><span class='hs-comment'>-- > .. XS.get :: X ListStorage</span>
<a name="line-56"></a><span class='hs-comment'>--</span>
<a name="line-57"></a><span class='hs-comment'>-- To make your data persistent between restarts, the data type needs to be</span>
<a name="line-58"></a><span class='hs-comment'>-- an instance of Read and Show and the instance declaration has to be changed:</span>
<a name="line-59"></a><span class='hs-comment'>--</span>
<a name="line-60"></a><span class='hs-comment'>-- > data ListStorage = ListStorage [Integer] deriving (Typeable,Read,Show)</span>
<a name="line-61"></a><span class='hs-comment'>-- ></span>
<a name="line-62"></a><span class='hs-comment'>-- > instance ExtensionClass ListStorage where</span>
<a name="line-63"></a><span class='hs-comment'>-- > initialValue = ListStorage []</span>
<a name="line-64"></a><span class='hs-comment'>-- > extensionType = PersistentExtension</span>
<a name="line-65"></a><span class='hs-comment'>--</span>
<a name="line-66"></a><span class='hs-comment'>-- One should take care that the string representation of the chosen type</span>
<a name="line-67"></a><span class='hs-comment'>-- is unique among the stored values, otherwise it will be overwritten.</span>
<a name="line-68"></a><span class='hs-comment'>-- Normally these string representations contain fully qualified module names</span>
<a name="line-69"></a><span class='hs-comment'>-- when automatically deriving Typeable, so</span>
<a name="line-70"></a><span class='hs-comment'>-- name collisions should not be a problem in most cases.</span>
<a name="line-71"></a><span class='hs-comment'>-- A module should not try to store common datatypes(e.g. a list of Integers)</span>
<a name="line-72"></a><span class='hs-comment'>-- without a custom data type as a wrapper to avoid collisions with other modules</span>
<a name="line-73"></a><span class='hs-comment'>-- trying to store the same data type without a wrapper.</span>
<a name="line-74"></a><span class='hs-comment'>--</span>
<a name="line-75"></a>
<a name="line-76"></a><a name="modifyStateExts"></a><span class='hs-comment'>-- | Modify the map of state extensions by applying the given function.</span>
<a name="line-77"></a><span class='hs-definition'>modifyStateExts</span> <span class='hs-keyglyph'>::</span> <span class='hs-layout'>(</span><span class='hs-conid'>M</span><span class='hs-varop'>.</span><span class='hs-conid'>Map</span> <span class='hs-conid'>String</span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-conid'>String</span> <span class='hs-conid'>StateExtension</span><span class='hs-layout'>)</span>
<a name="line-78"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>M</span><span class='hs-varop'>.</span><span class='hs-conid'>Map</span> <span class='hs-conid'>String</span> <span class='hs-layout'>(</span><span class='hs-conid'>Either</span> <span class='hs-conid'>String</span> <span class='hs-conid'>StateExtension</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-79"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>X</span> <span class='hs-conid'>()</span>
<a name="line-80"></a><span class='hs-definition'>modifyStateExts</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>State</span><span class='hs-varop'>.</span><span class='hs-varid'>modify</span> <span class='hs-varop'>$</span> <span class='hs-keyglyph'>\</span><span class='hs-varid'>st</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>st</span> <span class='hs-layout'>{</span> <span class='hs-varid'>extensibleState</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>f</span> <span class='hs-layout'>(</span><span class='hs-varid'>extensibleState</span> <span class='hs-varid'>st</span><span class='hs-layout'>)</span> <span class='hs-layout'>}</span>
<a name="line-81"></a>
<a name="line-82"></a><a name="modify"></a><span class='hs-comment'>-- | Apply a function to a stored value of the matching type or the initial value if there</span>
<a name="line-83"></a><span class='hs-comment'>-- is none.</span>
<a name="line-84"></a><span class='hs-definition'>modify</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>ExtensionClass</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>X</span> <span class='hs-conid'>()</span>
<a name="line-85"></a><span class='hs-definition'>modify</span> <span class='hs-varid'>f</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>put</span> <span class='hs-varop'>.</span> <span class='hs-varid'>f</span> <span class='hs-varop'>=<<</span> <span class='hs-varid'>get</span>
<a name="line-86"></a>
<a name="line-87"></a><a name="put"></a><span class='hs-comment'>-- | Add a value to the extensible state field. A previously stored value with the same</span>
<a name="line-88"></a><span class='hs-comment'>-- type will be overwritten. (More precisely: A value whose string representation of its type</span>
<a name="line-89"></a><span class='hs-comment'>-- is equal to the new one's)</span>
<a name="line-90"></a><span class='hs-definition'>put</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>ExtensionClass</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>X</span> <span class='hs-conid'>()</span>
<a name="line-91"></a><span class='hs-definition'>put</span> <span class='hs-varid'>v</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>modifyStateExts</span> <span class='hs-varop'>.</span> <span class='hs-conid'>M</span><span class='hs-varop'>.</span><span class='hs-varid'>insert</span> <span class='hs-layout'>(</span><span class='hs-varid'>show</span> <span class='hs-varop'>.</span> <span class='hs-varid'>typeOf</span> <span class='hs-varop'>$</span> <span class='hs-varid'>v</span><span class='hs-layout'>)</span> <span class='hs-varop'>.</span> <span class='hs-conid'>Right</span> <span class='hs-varop'>.</span> <span class='hs-varid'>extensionType</span> <span class='hs-varop'>$</span> <span class='hs-varid'>v</span>
<a name="line-92"></a>
<a name="line-93"></a><a name="get"></a><span class='hs-comment'>-- | Try to retrieve a value of the requested type, return an initial value if there is no such value.</span>
<a name="line-94"></a><span class='hs-definition'>get</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>ExtensionClass</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-conid'>X</span> <span class='hs-varid'>a</span>
<a name="line-95"></a><span class='hs-definition'>get</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>getState'</span> <span class='hs-varid'>undefined</span> <span class='hs-comment'>-- `trick' to avoid needing -XScopedTypeVariables</span>
<a name="line-96"></a> <span class='hs-keyword'>where</span> <span class='hs-varid'>toValue</span> <span class='hs-varid'>val</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>maybe</span> <span class='hs-varid'>initialValue</span> <span class='hs-varid'>id</span> <span class='hs-varop'>$</span> <span class='hs-varid'>cast</span> <span class='hs-varid'>val</span>
<a name="line-97"></a> <span class='hs-varid'>getState'</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>ExtensionClass</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>X</span> <span class='hs-varid'>a</span>
<a name="line-98"></a> <span class='hs-varid'>getState'</span> <span class='hs-varid'>k</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-99"></a> <span class='hs-varid'>v</span> <span class='hs-keyglyph'><-</span> <span class='hs-conid'>State</span><span class='hs-varop'>.</span><span class='hs-varid'>gets</span> <span class='hs-varop'>$</span> <span class='hs-conid'>M</span><span class='hs-varop'>.</span><span class='hs-varid'>lookup</span> <span class='hs-layout'>(</span><span class='hs-varid'>show</span> <span class='hs-varop'>.</span> <span class='hs-varid'>typeOf</span> <span class='hs-varop'>$</span> <span class='hs-varid'>k</span><span class='hs-layout'>)</span> <span class='hs-varop'>.</span> <span class='hs-varid'>extensibleState</span>
<a name="line-100"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>v</span> <span class='hs-keyword'>of</span>
<a name="line-101"></a> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-conid'>Right</span> <span class='hs-layout'>(</span><span class='hs-conid'>StateExtension</span> <span class='hs-varid'>val</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-varid'>toValue</span> <span class='hs-varid'>val</span>
<a name="line-102"></a> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-conid'>Right</span> <span class='hs-layout'>(</span><span class='hs-conid'>PersistentExtension</span> <span class='hs-varid'>val</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-varid'>toValue</span> <span class='hs-varid'>val</span>
<a name="line-103"></a> <span class='hs-conid'>Just</span> <span class='hs-layout'>(</span><span class='hs-conid'>Left</span> <span class='hs-varid'>str</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>PersistentExtension</span> <span class='hs-varid'>x</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>extensionType</span> <span class='hs-varid'>k</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-104"></a> <span class='hs-keyword'>let</span> <span class='hs-varid'>val</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>fromMaybe</span> <span class='hs-varid'>initialValue</span> <span class='hs-varop'>$</span> <span class='hs-varid'>cast</span> <span class='hs-varop'>=<<</span> <span class='hs-varid'>safeRead</span> <span class='hs-varid'>str</span> <span class='hs-varop'>`asTypeOf`</span> <span class='hs-conid'>Just</span> <span class='hs-varid'>x</span>
<a name="line-105"></a> <span class='hs-varid'>put</span> <span class='hs-layout'>(</span><span class='hs-varid'>val</span> <span class='hs-varop'>`asTypeOf`</span> <span class='hs-varid'>k</span><span class='hs-layout'>)</span>
<a name="line-106"></a> <span class='hs-varid'>return</span> <span class='hs-varid'>val</span>
<a name="line-107"></a> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>return</span> <span class='hs-varop'>$</span> <span class='hs-varid'>initialValue</span>
<a name="line-108"></a> <span class='hs-varid'>safeRead</span> <span class='hs-varid'>str</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>case</span> <span class='hs-varid'>reads</span> <span class='hs-varid'>str</span> <span class='hs-keyword'>of</span>
<a name="line-109"></a> <span class='hs-keyglyph'>[</span><span class='hs-layout'>(</span><span class='hs-varid'>x</span><span class='hs-layout'>,</span><span class='hs-str'>""</span><span class='hs-layout'>)</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Just</span> <span class='hs-varid'>x</span>
<a name="line-110"></a> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Nothing</span>
<a name="line-111"></a>
<a name="line-112"></a><a name="gets"></a><span class='hs-definition'>gets</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>ExtensionClass</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-layout'>(</span><span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>X</span> <span class='hs-varid'>b</span>
<a name="line-113"></a><span class='hs-definition'>gets</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>flip</span> <span class='hs-varid'>fmap</span> <span class='hs-varid'>get</span>
<a name="line-114"></a>
<a name="line-115"></a><a name="remove"></a><span class='hs-comment'>-- | Remove the value from the extensible state field that has the same type as the supplied argument</span>
<a name="line-116"></a><span class='hs-definition'>remove</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>ExtensionClass</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=></span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>X</span> <span class='hs-conid'>()</span>
<a name="line-117"></a><span class='hs-definition'>remove</span> <span class='hs-varid'>wit</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>modifyStateExts</span> <span class='hs-varop'>$</span> <span class='hs-conid'>M</span><span class='hs-varop'>.</span><span class='hs-varid'>delete</span> <span class='hs-layout'>(</span><span class='hs-varid'>show</span> <span class='hs-varop'>.</span> <span class='hs-varid'>typeOf</span> <span class='hs-varop'>$</span> <span class='hs-varid'>wit</span><span class='hs-layout'>)</span>
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