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<title>Attributes of Nonterminals</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="spirit_x3.abstracts.nonterminal_attributes"></a><a class="link" href="nonterminal_attributes.html" title="Attributes of Nonterminals">Attributes
      of Nonterminals</a>
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<p>
        Nonterminals are the main means of constructing more complex parsers out
        of simpler ones. The nonterminals in the parser world are very similar to
        functions in an imperative programming language. They can be used to encapsulate
        parser expressions for a particular input sequence. After being defined,
        the nonterminals can be used as 'normal' parsers in more complex expressions
        whenever the encapsulated input needs to be recognized. Parser nonterminals
        in <span class="emphasis"><em>Spirit.X3</em></span> usually return a value (the synthesized
        attribute).
      </p>
<p>
        The type of the synthesized attribute as to be explicitly specified while
        defining the particular nonterminal. Example (ignore ID for now):
      </p>
<pre class="programlisting"><span class="identifier">x3</span><span class="special">::</span><span class="identifier">rule</span><span class="special">&lt;</span><span class="identifier">ID</span><span class="special">,</span> <span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">r</span><span class="special">;</span>
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