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<title>Batteries user guide : Extlib.Option</title>
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<h1>Module <a href="type_Extlib.Option.html">Extlib.Option</a></h1>
<pre><span class="keyword">module</span> Option: <code class="type">BatOption</code></pre><hr width="100%">
<pre><span id="TYPEt"><span class="keyword">type</span> <code class="type">'a</code> t</span> = <code class="type">'a option</code> </pre>
<pre><span id="VALmay"><span class="keyword">val</span> may</span> : <code class="type">('a -> unit) -> 'a option -> unit</code></pre><div class="info ">
<code class="code">may f (<span class="constructor">Some</span> x)</code> calls <code class="code">f x</code> and <code class="code">may f <span class="constructor">None</span></code> does nothing.<br>
</div>
<pre><span id="VALmap"><span class="keyword">val</span> map</span> : <code class="type">('a -> 'b) -> 'a option -> 'b option</code></pre><div class="info ">
<code class="code">map f (<span class="constructor">Some</span> x)</code> returns <code class="code"><span class="constructor">Some</span> (f x)</code> and <code class="code">map f <span class="constructor">None</span></code> returns <code class="code"><span class="constructor">None</span></code>.<br>
</div>
<pre><span id="VALbind"><span class="keyword">val</span> bind</span> : <code class="type">'a option -> ('a -> 'b option) -> 'b option</code></pre><div class="info ">
<code class="code">bind (<span class="constructor">Some</span> x) f</code> returns <code class="code">f x</code> and <code class="code">bind <span class="constructor">None</span> f</code> returns <code class="code"><span class="constructor">None</span></code>.<br>
</div>
<pre><span id="VALapply"><span class="keyword">val</span> apply</span> : <code class="type">('a -> 'a) option -> 'a -> 'a</code></pre><div class="info ">
<code class="code">apply <span class="constructor">None</span> x</code> returns <code class="code">x</code> and <code class="code">apply (<span class="constructor">Some</span> f) x</code> returns <code class="code">f x</code><br>
</div>
<pre><span id="VALfilter"><span class="keyword">val</span> filter</span> : <code class="type">('a -> bool) -> 'a option -> 'a option</code></pre><div class="info ">
<code class="code">filter f <span class="constructor">None</span></code> returns <code class="code"><span class="constructor">None</span></code>, <code class="code">filter f (<span class="constructor">Some</span> x)</code> returns <code class="code"><span class="constructor">Some</span> x</code>
if <code class="code">f x</code> is true, and <code class="code"><span class="constructor">None</span></code> otherwise.<br>
</div>
<pre><span id="VALdefault"><span class="keyword">val</span> default</span> : <code class="type">'a -> 'a option -> 'a</code></pre><div class="info ">
<code class="code">default x (<span class="constructor">Some</span> v)</code> returns <code class="code">v</code> and <code class="code">default x <span class="constructor">None</span></code> returns <code class="code">x</code>.<br>
</div>
<pre><span id="VAL(|?)"><span class="keyword">val</span> (|?)</span> : <code class="type">'a option -> 'a -> 'a</code></pre><div class="info ">
Like <a href="BatOption.html#VALdefault"><code class="code"><span class="constructor">BatOption</span>.default</code></a>, with the arguments reversed.
<code class="code"><span class="constructor">None</span> |? 10</code> returns <code class="code">10</code>, while <code class="code"><span class="constructor">Some</span> <span class="string">"foo"</span> |? <span class="string">"bar"</span></code> returns <code class="code"><span class="string">"foo"</span></code>.
<p>
<b>Note</b> This operator does not short circuit like <code class="code">( <span class="keywordsign">||</span> )</code> and <code class="code">( <span class="keywordsign">&&</span> )</code>.
Both arguments will be evaluated.<br>
<b>Since</b> 2.0<br>
</div>
<pre><span id="VALdefault_delayed"><span class="keyword">val</span> default_delayed</span> : <code class="type">(unit -> 'a) -> 'a option -> 'a</code></pre><div class="info ">
Like <a href="BatOption.html#VALdefault"><code class="code"><span class="constructor">BatOption</span>.default</code></a>, but the default value is passed as a thunk that
is only computed if needed.<br>
<b>Since</b> 2.1<br>
</div>
<pre><span id="VALmap_default"><span class="keyword">val</span> map_default</span> : <code class="type">('a -> 'b) -> 'b -> 'a option -> 'b</code></pre><div class="info ">
<code class="code">map_default f x (<span class="constructor">Some</span> v)</code> returns <code class="code">f v</code> and <code class="code">map_default f x <span class="constructor">None</span></code>
returns <code class="code">x</code>.<br>
</div>
<pre><span id="VALmap_default_delayed"><span class="keyword">val</span> map_default_delayed</span> : <code class="type">('a -> 'b) -> (unit -> 'b) -> 'a option -> 'b</code></pre><div class="info ">
Like <a href="BatOption.html#VALmap_default"><code class="code"><span class="constructor">BatOption</span>.map_default</code></a>, but the default value is passed as a thunk that
is only computed if needed.<br>
<b>Since</b> 2.1<br>
</div>
<pre><span id="VALis_none"><span class="keyword">val</span> is_none</span> : <code class="type">'a option -> bool</code></pre><div class="info ">
<code class="code">is_none <span class="constructor">None</span></code> returns <code class="code"><span class="keyword">true</span></code> otherwise it returns <code class="code"><span class="keyword">false</span></code>.<br>
</div>
<pre><span id="VALis_some"><span class="keyword">val</span> is_some</span> : <code class="type">'a option -> bool</code></pre><div class="info ">
<code class="code">is_some (<span class="constructor">Some</span> x)</code> returns <code class="code"><span class="keyword">true</span></code> otherwise it returns <code class="code"><span class="keyword">false</span></code>.<br>
</div>
<pre><span id="VALget"><span class="keyword">val</span> get</span> : <code class="type">'a option -> 'a</code></pre><div class="info ">
<code class="code">get (<span class="constructor">Some</span> x)</code> returns <code class="code">x</code>.<br>
<b>Raises</b> <code>Invalid_argument</code> on <code class="code">get <span class="constructor">None</span></code>.<br>
</div>
<pre><span id="VALget_exn"><span class="keyword">val</span> get_exn</span> : <code class="type">'a option -> exn -> 'a</code></pre><div class="info ">
<code class="code">get_exn (<span class="constructor">Some</span> x) e</code> returns <code class="code">x</code> and <code class="code">get_exn <span class="constructor">None</span> e</code> raises <code class="code">e</code>.<br>
</div>
<pre><span id="VALcompare"><span class="keyword">val</span> compare</span> : <code class="type">?cmp:('a -> 'a -> int) -> 'a option -> 'a option -> int</code></pre><div class="info ">
Compare two options, possibly using custom comparators for the
value. <code class="code"><span class="constructor">None</span></code> is always assumed to be less than <code class="code"><span class="constructor">Some</span> _</code>. The
parameter <code class="code">cmp</code> defaults to <code class="code"><span class="constructor">Pervasives</span>.compare</code>.<br>
</div>
<pre><span id="VALeq"><span class="keyword">val</span> eq</span> : <code class="type">?eq:('a -> 'a -> bool) -> 'a option -> 'a option -> bool</code></pre><div class="info ">
Test for equality between option types, possibly using a custom
equality predicate. The parameter <code class="code">eq</code> defaults to
<code class="code"><span class="constructor">Pervasives</span>.(=)</code>.<br>
<b>Since</b> 1.4.0<br>
</div>
<pre><span id="VALenum"><span class="keyword">val</span> enum</span> : <code class="type">'a option -> 'a <a href="BatEnum.html#TYPEt">BatEnum.t</a></code></pre><div class="info ">
<code class="code">enum (<span class="constructor">Some</span> x)</code> returns the singleton <code class="code">x</code>, while <code class="code">enum <span class="constructor">None</span></code> returns
the empty enumeration.<br>
</div>
<pre><span id="VALof_enum"><span class="keyword">val</span> of_enum</span> : <code class="type">'a <a href="BatEnum.html#TYPEt">BatEnum.t</a> -> 'a option</code></pre><div class="info ">
<code class="code">of_enum e</code> consumes the first element of <code class="code">e</code>, if it exists, and
returns <code class="code"><span class="constructor">Some</span> e</code>. If <code class="code">e</code> is empty, return <code class="code"><span class="constructor">None</span></code>.<br>
</div>
<br>
<h6 id="6_TheOptionMonad">The Option Monad</h6><br>
<pre><span class="keyword">module</span> <a href="BatOption.Monad.html">Monad</a>: <code class="code"><span class="keyword">sig</span></code> <a href="BatOption.Monad.html">..</a> <code class="code"><span class="keyword">end</span></code></pre><div class="info">
This module provides everything needed to write and execute computations
in the Option monad.
</div>
<br>
<h6 id="6_Boilerplatecode">Boilerplate code</h6><br>
<br>
<div class="h7" id="7_Printing">Printing</div><br>
<pre><span id="VALprint"><span class="keyword">val</span> print</span> : <code class="type">('a <a href="BatInnerIO.html#TYPEoutput">BatInnerIO.output</a> -> 'b -> unit) -><br> 'a <a href="BatInnerIO.html#TYPEoutput">BatInnerIO.output</a> -> 'b <a href="BatOption.html#TYPEt">t</a> -> unit</code></pre>
<pre><span class="keyword">module</span> <a href="BatOption.Labels.html">Labels</a>: <code class="code"><span class="keyword">sig</span></code> <a href="BatOption.Labels.html">..</a> <code class="code"><span class="keyword">end</span></code></pre><div class="info">
Operations on options, with labels.
</div>
<pre><span class="keyword">module</span> <a href="BatOption.Infix.html">Infix</a>: <code class="code"><span class="keyword">sig</span></code> <a href="BatOption.Infix.html">..</a> <code class="code"><span class="keyword">end</span></code></pre></body></html>
