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<h3 class="unnumberedsec">Why doesn&rsquo;t flex have non-greedy operators like perl does?</h3>

<p>A DFA can do a non-greedy match by stopping
the first time it enters an accepting state, instead of consuming input until
it determines that no further matching is possible (a &ldquo;jam&rdquo; state).  This
is actually easier to implement than longest leftmost match (which flex does).
</p>
<p>But it&rsquo;s also much less useful than longest leftmost match.  In general,
when you find yourself wishing for non-greedy matching, that&rsquo;s usually a
sign that you&rsquo;re trying to make the scanner do some parsing.  That&rsquo;s
generally the wrong approach, since it lacks the power to do a decent job.
Better is to either introduce a separate parser, or to split the scanner
into multiple scanners using (exclusive) start conditions.
</p>
<p>You might have
a separate start state once you&rsquo;ve seen the &lsquo;<samp>BEGIN</samp>&rsquo;. In that state, you
might then have a regex that will match &lsquo;<samp>END</samp>&rsquo; (to kick you out of the
state), and perhaps &lsquo;<samp>(.|\n)</samp>&rsquo; to get a single character within the chunk ...
</p>
<p>This approach also has much better error-reporting properties.
</p>



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flex-doc 2.6.4-6 / usr / share / doc / flex-doc / html / Why-doesn_0027t-flex-have-non_002dgreedy-operators-like-perl-does_003f.html
