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<a href="./Home">MLton 20201002</a>
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<h1>LineDirective</h1>
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<div class="paragraph"><p>To aid in the debugging of code produced by program generators such
as <a href="http://www.eecs.harvard.edu/%7Enr/noweb/">Noweb</a>, MLton supports
comments with line directives of the form</p></div>
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<div class="content"><div class="highlight"><pre><span></span><span class="cm">(*#line l.c &quot;f&quot;*)</span><span class="w"></span>
</pre></div></div></div>
<div class="paragraph"><p>Here, <em>l</em> and <em>c</em> are sequences of decimal digits and <em>f</em> is the
source file.  The first character of a source file has the position
1.1.  A line directive causes the front end to believe that the
character following the right parenthesis is at the line and column of
the specified file.  A line directive only affects the reporting of
error messages and does not affect program semantics (except for
functions like <span class="monospaced">MLton.Exn.history</span> that report source file positions).
Syntactically invalid line directives are ignored.  To prevent
incompatibilities with SML, the file name may not contain the
character sequence <span class="monospaced">*)</span>.</p></div>
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