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  <p class="right" id="maybe-0"><span id="index-0"></span><strong>object</strong></p>
<section id="maybe">
<h1><code class="docutils literal notranslate"><span class="pre">maybe</span></code><a class="headerlink" href="#maybe" title="Link to this heading"></a></h1>
<p>Types and predicates for type-checking and handling optional terms. Inspired by Haskell.</p>
<div class="line-block">
<div class="line"><strong>Availability:</strong></div>
<div class="line-block">
<div class="line"><code class="docutils literal notranslate"><span class="pre">logtalk_load(optionals(loader))</span></code></div>
</div>
</div>
<div class="line-block">
<div class="line"><strong>Author:</strong> Paulo Moura</div>
<div class="line"><strong>Version:</strong> 0:7:0</div>
<div class="line"><strong>Date:</strong> 2021-01-03</div>
</div>
<div class="line-block">
<div class="line"><strong>Compilation flags:</strong></div>
<div class="line-block">
<div class="line"><code class="docutils literal notranslate"><span class="pre">static,</span> <span class="pre">context_switching_calls</span></code></div>
</div>
</div>
<div class="line-block">
<div class="line"><strong>Provides:</strong></div>
<div class="line-block">
<div class="line"><a class="reference internal" href="type_0.html#type-0-type-1"><span class="std std-ref">type::type/1</span></a></div>
<div class="line"><a class="reference internal" href="type_0.html#type-0-check-2"><span class="std std-ref">type::check/2</span></a></div>
<div class="line"><a class="reference internal" href="arbitrary_0.html#arbitrary-0-arbitrary-1"><span class="std std-ref">arbitrary::arbitrary/1</span></a></div>
<div class="line"><a class="reference internal" href="arbitrary_0.html#arbitrary-0-arbitrary-2"><span class="std std-ref">arbitrary::arbitrary/2</span></a></div>
</div>
<div class="line"><strong>Uses:</strong></div>
<div class="line-block">
<div class="line"><a class="reference internal" href="optional_0.html#optional-0"><span class="std std-ref">optional</span></a></div>
<div class="line"><a class="reference internal" href="optional_1.html#optional-1"><span class="std std-ref">optional(Optional)</span></a></div>
<div class="line"><a class="reference internal" href="random_0.html#random-0"><span class="std std-ref">random</span></a></div>
<div class="line"><a class="reference internal" href="type_0.html#type-0"><span class="std std-ref">type</span></a></div>
</div>
</div>
<div class="line-block">
<div class="line"><strong>Remarks:</strong></div>
</div>
<blockquote>
<div><ul class="simple">
<li><p>Type-checking support: Defines type <code class="docutils literal notranslate"><span class="pre">maybe(Type)</span></code> for checking optional terms where the value hold by the optional term must be of the given type.</p></li>
<li><p>QuickCheck support: Defines clauses for the <code class="docutils literal notranslate"><span class="pre">arbitrary::arbitrary/1-2</span></code> predicates to allow generating random values for the <code class="docutils literal notranslate"><span class="pre">maybe(Type)</span></code> type.</p></li>
</ul>
</div></blockquote>
<div class="line-block">
<div class="line"><strong>Inherited public predicates:</strong></div>
<div class="line-block">
<div class="line">(none)</div>
</div>
</div>
<nav class="contents local" id="contents">
<ul class="simple">
<li><p><a class="reference internal" href="#public-predicates" id="id1">Public predicates</a></p>
<ul>
<li><p><a class="reference internal" href="#cat-2" id="id2"><code class="docutils literal notranslate"><span class="pre">cat/2</span></code></a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#protected-predicates" id="id3">Protected predicates</a></p></li>
<li><p><a class="reference internal" href="#private-predicates" id="id4">Private predicates</a></p></li>
<li><p><a class="reference internal" href="#operators" id="id5">Operators</a></p></li>
</ul>
</nav>
<section id="public-predicates">
<h2><a class="toc-backref" href="#contents" role="doc-backlink">Public predicates</a><a class="headerlink" href="#public-predicates" title="Link to this heading"></a></h2>
<section id="cat-2">
<span id="maybe-0-cat-2"></span><span id="index-1"></span><h3><a class="toc-backref" href="#contents" role="doc-backlink"><code class="docutils literal notranslate"><span class="pre">cat/2</span></code></a><a class="headerlink" href="#cat-2" title="Link to this heading"></a></h3>
<p>Returns the values stored in the non-empty optional terms.</p>
<div class="line-block">
<div class="line"><strong>Compilation flags:</strong></div>
<div class="line-block">
<div class="line"><code class="docutils literal notranslate"><span class="pre">static</span></code></div>
</div>
</div>
<div class="line-block">
<div class="line"><strong>Template:</strong></div>
<div class="line-block">
<div class="line"><code class="docutils literal notranslate"><span class="pre">cat(Optionals,Values)</span></code></div>
</div>
<div class="line"><strong>Mode and number of proofs:</strong></div>
<div class="line-block">
<div class="line"><code class="docutils literal notranslate"><span class="pre">cat(+list(optional),-list)</span></code> - <code class="docutils literal notranslate"><span class="pre">one</span></code></div>
</div>
</div>
</section>
</section>
<hr class="docutils" />
<section id="protected-predicates">
<h2><a class="toc-backref" href="#contents" role="doc-backlink">Protected predicates</a><a class="headerlink" href="#protected-predicates" title="Link to this heading"></a></h2>
<p>(no local declarations; see entity ancestors if any)</p>
</section>
<section id="private-predicates">
<h2><a class="toc-backref" href="#contents" role="doc-backlink">Private predicates</a><a class="headerlink" href="#private-predicates" title="Link to this heading"></a></h2>
<p>(no local declarations; see entity ancestors if any)</p>
</section>
<section id="operators">
<h2><a class="toc-backref" href="#contents" role="doc-backlink">Operators</a><a class="headerlink" href="#operators" title="Link to this heading"></a></h2>
<p>(none)</p>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
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