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<title>Why can't flex understand this variable trailing context pattern? (Lexical Analysis With Flex, for Flex 2.6.4)</title>

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<h3 class="unnumberedsec">Why can&rsquo;t flex understand this variable trailing context pattern?</h3>
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<pre class="verbatim">To: Gregory Margo &lt;gmargo@newton.vip.best.com&gt;
Subject: Re: flex-2.5.3 bug report
In-reply-to: Your message of Sat, 23 Nov 1996 16:50:09 PST.
Date: Sat, 23 Nov 1996 17:07:32 PST
From: Vern Paxson &lt;vern&gt;

&gt; Enclosed is a lex file that &quot;real&quot; lex will process, but I cannot get
&gt; flex to process it.  Could you try it and maybe point me in the right direction?

Your problem is that some of the definitions in the scanner use the '/'
trailing context operator, and have it enclosed in ()'s.  Flex does not
allow this operator to be enclosed in ()'s because doing so allows undefined
regular expressions such as &quot;(a/b)+&quot;.  So the solution is to remove the
parentheses.  Note that you must also be building the scanner with the -l
option for AT&amp;T lex compatibility.  Without this option, flex automatically
encloses the definitions in parentheses.

		Vern
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flex-doc 2.6.4-6 / usr / share / doc / flex-doc / html / Why-can_0027t-flex-understand-this-variable-trailing-context-pattern_003f.html
