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<title>Option</title>
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<h1>Module <a href="type_Option.html">Option</a></h1>
<pre><span id="MODULEOption"><span class="keyword">module</span> Option</span>: <code class="code"><span class="keyword">sig</span></code> <a href="Option.html">..</a> <code class="code"><span class="keyword">end</span></code></pre><div class="info module top">
<div class="info-desc">
<p>Option values.</p>
<p>Option values explicitly indicate the presence or absence of a value.</p>
</div>
<ul class="info-attributes">
<li><b>Since</b> 4.08</li>
</ul>
</div>
<hr width="100%">
<h2 id="options">Options</h2>
<pre><span id="TYPEt"><span class="keyword">type</span> <code class="type">'a</code> t</span> = <code class="type">'a option</code> = </pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTt.None"><span class="constructor">None</span></span></code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code><span class="keyword">|</span></code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTt.Some"><span class="constructor">Some</span></span> <span class="keyword">of</span> <code class="type">'a</code></code></td>
</tr></table>
<div class="info ">
<div class="info-desc">
<p>The type for option values. Either <code class="code"><span class="constructor">None</span></code> or a value <code class="code"><span class="constructor">Some</span> v</code>.</p>
</div>
</div>
<pre><span id="VALnone"><span class="keyword">val</span> none</span> : <code class="type">'a option</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">none</code> is <code class="code"><span class="constructor">None</span></code>.</p>
</div>
</div>
<pre><span id="VALsome"><span class="keyword">val</span> some</span> : <code class="type">'a -> 'a option</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">some v</code> is <code class="code"><span class="constructor">Some</span> v</code>.</p>
</div>
</div>
<pre><span id="VALvalue"><span class="keyword">val</span> value</span> : <code class="type">'a option -> default:'a -> 'a</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">value o ~default</code> is <code class="code">v</code> if <code class="code">o</code> is <code class="code"><span class="constructor">Some</span> v</code> and <code class="code">default</code> otherwise.</p>
</div>
</div>
<pre><span id="VALget"><span class="keyword">val</span> get</span> : <code class="type">'a option -> 'a</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">get o</code> is <code class="code">v</code> if <code class="code">o</code> is <code class="code"><span class="constructor">Some</span> v</code> and</p>
</div>
<ul class="info-attributes">
<li><b>Raises</b> <code>Invalid_argument</code> otherwise.</li>
</ul>
</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 ">
<div class="info-desc">
<p><code class="code">bind o f</code> is <code class="code">f v</code> if <code class="code">o</code> is <code class="code"><span class="constructor">Some</span> v</code> and <code class="code"><span class="constructor">None</span></code> if <code class="code">o</code> is <code class="code"><span class="constructor">None</span></code>.</p>
</div>
</div>
<pre><span id="VALjoin"><span class="keyword">val</span> join</span> : <code class="type">'a option option -> 'a option</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">join oo</code> is <code class="code"><span class="constructor">Some</span> v</code> if <code class="code">oo</code> is <code class="code"><span class="constructor">Some</span> (<span class="constructor">Some</span> v)</code> and <code class="code"><span class="constructor">None</span></code> otherwise.</p>
</div>
</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 ">
<div class="info-desc">
<p><code class="code">map f o</code> is <code class="code"><span class="constructor">None</span></code> if <code class="code">o</code> is <code class="code"><span class="constructor">None</span></code> and <code class="code"><span class="constructor">Some</span> (f v)</code> is <code class="code">o</code> is <code class="code"><span class="constructor">Some</span> v</code>.</p>
</div>
</div>
<pre><span id="VALfold"><span class="keyword">val</span> fold</span> : <code class="type">none:'a -> some:('b -> 'a) -> 'b option -> 'a</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">fold ~none ~some o</code> is <code class="code">none</code> if <code class="code">o</code> is <code class="code"><span class="constructor">None</span></code> and <code class="code">some v</code> if <code class="code">o</code> is
<code class="code"><span class="constructor">Some</span> v</code>.</p>
</div>
</div>
<pre><span id="VALiter"><span class="keyword">val</span> iter</span> : <code class="type">('a -> unit) -> 'a option -> unit</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">iter f o</code> is <code class="code">f v</code> if <code class="code">o</code> is <code class="code"><span class="constructor">Some</span> v</code> and <code class="code">()</code> otherwise.</p>
</div>
</div>
<h2 id="preds">Predicates and comparisons</h2>
<pre><span id="VALis_none"><span class="keyword">val</span> is_none</span> : <code class="type">'a option -> bool</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">is_none o</code> is <code class="code"><span class="keyword">true</span></code> iff <code class="code">o</code> is <code class="code"><span class="constructor">None</span></code>.</p>
</div>
</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 ">
<div class="info-desc">
<p><code class="code">is_some o</code> is <code class="code"><span class="keyword">true</span></code> iff <code class="code">o</code> is <code class="code"><span class="constructor">Some</span> o</code>.</p>
</div>
</div>
<pre><span id="VALequal"><span class="keyword">val</span> equal</span> : <code class="type">('a -> 'a -> bool) -> 'a option -> 'a option -> bool</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">equal eq o0 o1</code> is <code class="code"><span class="keyword">true</span></code> iff <code class="code">o0</code> and <code class="code">o1</code> are both <code class="code"><span class="constructor">None</span></code> or if
they are <code class="code"><span class="constructor">Some</span> v0</code> and <code class="code"><span class="constructor">Some</span> v1</code> and <code class="code">eq v0 v1</code> is <code class="code"><span class="keyword">true</span></code>.</p>
</div>
</div>
<pre><span id="VALcompare"><span class="keyword">val</span> compare</span> : <code class="type">('a -> 'a -> int) -> 'a option -> 'a option -> int</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">compare cmp o0 o1</code> is a total order on options using <code class="code">cmp</code> to compare
values wrapped by <code class="code"><span class="constructor">Some</span> _</code>. <code class="code"><span class="constructor">None</span></code> is smaller than <code class="code"><span class="constructor">Some</span> _</code> values.</p>
</div>
</div>
<h2 id="convert">Converting</h2>
<pre><span id="VALto_result"><span class="keyword">val</span> to_result</span> : <code class="type">none:'e -> 'a option -> ('a, 'e) <a href="Stdlib.html#TYPEresult">result</a></code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">to_result ~none o</code> is <code class="code"><span class="constructor">Ok</span> v</code> if <code class="code">o</code> is <code class="code"><span class="constructor">Some</span> v</code> and <code class="code"><span class="constructor">Error</span> none</code>
otherwise.</p>
</div>
</div>
<pre><span id="VALto_list"><span class="keyword">val</span> to_list</span> : <code class="type">'a option -> 'a list</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">to_list o</code> is <code class="code">[]</code> if <code class="code">o</code> is <code class="code"><span class="constructor">None</span></code> and <code class="code">[v]</code> if <code class="code">o</code> is <code class="code"><span class="constructor">Some</span> v</code>.</p>
</div>
</div>
<pre><span id="VALto_seq"><span class="keyword">val</span> to_seq</span> : <code class="type">'a option -> 'a <a href="Seq.html#TYPEt">Seq.t</a></code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">to_seq o</code> is <code class="code">o</code> as a sequence. <code class="code"><span class="constructor">None</span></code> is the empty sequence and
<code class="code"><span class="constructor">Some</span> v</code> is the singleton sequence containing <code class="code">v</code>.</p>
</div>
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