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<title>Preprocessor Intro (The GNU Troff Manual)</title>
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<h3 class="section" id="Preprocessors">1.5 Preprocessors</h3>
<a class="index-entry-id" id="index-preprocessors"></a>
<p>An alternative approach to complexity management, particularly when
constructing tables, setting mathematics, or drawing diagrams, lies in
preprocessing. A <em class="dfn">preprocessor</em> employs a domian-specific language
to ease the generation of tables, equations, and so forth in terms that
are convenient for human entry. Each preprocessor reads a document and
translates the parts of it that apply to it into GNU <code class="code">troff</code> input.
Command-line options to <code class="command">groff</code> tell it which preprocessors to
use.
</p>
<p><code class="code">groff</code> provides preprocessors for laying out tables
(<code class="command">gtbl</code>), typesetting equations (<code class="command">geqn</code>), drawing
diagrams (<code class="command">gpic</code> and <code class="command">ggrn</code>), inserting bibliographic
references (<code class="command">grefer</code>), and drawing chemical structures
(<code class="command">gchem</code>). An associated program that is useful when dealing
with preprocessors is <code class="command">gsoelim</code>.<a class="footnote" id="DOCF1" href="groff.html_fot.html#FOOT1"><sup>1</sup></a>
</p>
<p><code class="code">groff</code> also supports <code class="code">grap</code>, a preprocessor for drawing
graphs. A free implementation of it can be obtained separately.
</p>
<p>Unique to <code class="code">groff</code> is the <code class="code">preconv</code> preprocessor that enables
<code class="code">groff</code> to handle documents in a variety of input encodings.
</p>
<p>Other preprocessors exist, but no free implementations
are known. An example is <code class="command">ideal</code>, which draws diagrams using a
mathematical constraint language.
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