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</script></head><body><div id="package-header"><ul class="links" id="page-menu"><li><a href="src/Data-Either-Extra.html">Source</a></li><li><a href="index.html">Contents</a></li><li><a href="doc-index.html">Index</a></li></ul><p class="caption">extra-1.4.10: Extra functions I use.</p></div><div id="content"><div id="module-header"><table class="info"><tr><th>Safe Haskell</th><td>Safe</td></tr><tr><th>Language</th><td>Haskell2010</td></tr></table><p class="caption">Data.Either.Extra</p></div><div id="description"><p class="caption">Description</p><div class="doc"><p>This module extends <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html">Data.Either</a> with extra operations, particularly
to quickly extract from inside an <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a></code>. Some of these operations are
partial, and should be used with care in production-quality code.</p></div></div><div id="synopsis"><p id="control.syn" class="caption expander" onclick="toggleSection('syn')">Synopsis</p><ul id="section.syn" class="hide" onclick="toggleSection('syn')"><li class="src short">module <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html">Data.Either</a></li><li class="src short"><a href="#v:isLeft">isLeft</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a> a b -> <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Bool.html#t:Bool">Bool</a></li><li class="src short"><a href="#v:isRight">isRight</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a> a b -> <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Bool.html#t:Bool">Bool</a></li><li class="src short"><a href="#v:fromLeft">fromLeft</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a> l r -> l</li><li class="src short"><a href="#v:fromRight">fromRight</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a> l r -> r</li><li class="src short"><a href="#v:fromEither">fromEither</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a> a a -> a</li></ul></div><div id="interface"><h1>Documentation</h1><div class="top"><p class="src">module <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html">Data.Either</a></p></div><div class="top"><p class="src"><a id="v:isLeft" class="def">isLeft</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a> a b -> <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Bool.html#t:Bool">Bool</a> <a href="#v:isLeft" class="selflink">#</a></p><div class="doc"><p>Return <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Bool.html#v:True">True</a></code> if the given value is a <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#v:Left">Left</a></code>-value, <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Bool.html#v:False">False</a></code> otherwise.</p><h4 id="control.ch:isLeft0" class="caption expander" onclick="toggleSection('ch:isLeft0')">Examples</h4><div id="section.ch:isLeft0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>isLeft (Left "foo")
</code></strong>True
<code class="prompt">>>> </code><strong class="userinput"><code>isLeft (Right 3)
</code></strong>False
</pre><p>Assuming a <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#v:Left">Left</a></code> value signifies some sort of error, we can use
<code><a href="Data-Either-Extra.html#v:isLeft">isLeft</a></code> to write a very simple error-reporting function that does
absolutely nothing in the case of success, and outputs "ERROR" if
any error occurred.</p><p>This example shows how <code><a href="Data-Either-Extra.html#v:isLeft">isLeft</a></code> might be used to avoid pattern
matching when one does not care about the value contained in the
constructor:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>import Control.Monad ( when )
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>let report e = when (isLeft e) $ putStrLn "ERROR"
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>report (Right 1)
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>report (Left "parse error")
</code></strong>ERROR
</pre></div><p><em>Since: 4.7.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:isRight" class="def">isRight</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a> a b -> <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Bool.html#t:Bool">Bool</a> <a href="#v:isRight" class="selflink">#</a></p><div class="doc"><p>Return <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Bool.html#v:True">True</a></code> if the given value is a <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#v:Right">Right</a></code>-value, <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Bool.html#v:False">False</a></code> otherwise.</p><h4 id="control.ch:isRight0" class="caption expander" onclick="toggleSection('ch:isRight0')">Examples</h4><div id="section.ch:isRight0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>isRight (Left "foo")
</code></strong>False
<code class="prompt">>>> </code><strong class="userinput"><code>isRight (Right 3)
</code></strong>True
</pre><p>Assuming a <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#v:Left">Left</a></code> value signifies some sort of error, we can use
<code><a href="Data-Either-Extra.html#v:isRight">isRight</a></code> to write a very simple reporting function that only
outputs "SUCCESS" when a computation has succeeded.</p><p>This example shows how <code><a href="Data-Either-Extra.html#v:isRight">isRight</a></code> might be used to avoid pattern
matching when one does not care about the value contained in the
constructor:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>import Control.Monad ( when )
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>let report e = when (isRight e) $ putStrLn "SUCCESS"
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>report (Left "parse error")
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>report (Right 1)
</code></strong>SUCCESS
</pre></div><p><em>Since: 4.7.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:fromLeft" class="def">fromLeft</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a> l r -> l <a href="src/Data-Either-Extra.html#fromLeft" class="link">Source</a> <a href="#v:fromLeft" class="selflink">#</a></p><div class="doc"><p>The <code><a href="Data-Either-Extra.html#v:fromLeft">fromLeft</a></code> function extracts the element out of a <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#v:Left">Left</a></code> and
throws an error if its argument is <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#v:Right">Right</a></code>.
Much like <code>fromJust</code>, using this function in polished code is usually a bad idea.</p><pre>\x -> fromLeft (Left x) == x
\x -> fromLeft (Right x) == undefined</pre></div></div><div class="top"><p class="src"><a id="v:fromRight" class="def">fromRight</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a> l r -> r <a href="src/Data-Either-Extra.html#fromRight" class="link">Source</a> <a href="#v:fromRight" class="selflink">#</a></p><div class="doc"><p>The <code><a href="Data-Either-Extra.html#v:fromRight">fromRight</a></code> function extracts the element out of a <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#v:Right">Right</a></code> and
throws an error if its argument is <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#v:Left">Left</a></code>.
Much like <code>fromJust</code>, using this function in polished code is usually a bad idea.</p><pre>\x -> fromRight (Right x) == x
\x -> fromRight (Left x) == undefined</pre></div></div><div class="top"><p class="src"><a id="v:fromEither" class="def">fromEither</a> :: <a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a> a a -> a <a href="src/Data-Either-Extra.html#fromEither" class="link">Source</a> <a href="#v:fromEither" class="selflink">#</a></p><div class="doc"><p>Pull the value out of an <code><a href="file:///usr/share/doc/ghc-doc/html/libraries/base-4.9.0.0/Data-Either.html#t:Either">Either</a></code> where both alternatives
have the same type.</p><pre>\x -> fromEither (Left x ) == x
\x -> fromEither (Right x) == x</pre></div></div></div></div><div id="footer"><p>Produced by <a href="http://www.haskell.org/haddock/">Haddock</a> version 2.17.2</p></div></body></html>
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