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From: garrity@garrity.applicon.UUCP
Newsgroups: comp.unix.questions
Subject: Re: Any LEX gurus?
Message-ID: <35800010@garrity>
Date: Thu, 13-Aug-87 09:50:00 EDT
Article-I.D.: garrity.35800010
Posted: Thu Aug 13 09:50:00 1987
Date-Received: Sun, 16-Aug-87 23:13:31 EDT
References: <1031@ius1.cs.cmu.edu>
Lines: 43
Nf-ID: #R:ius1.cs.cmu.edu:-103100:garrity:35800010:000:1701
Nf-From: garrity.applicon.UUCP!garrity    Aug 13 09:50:00 1987


>> I am using (trying to use) LEX (& YACC, of course) to write a parser
>> for a language, and I'm running into problems defining some regular
>> expressions that need to be fed to LEX.  In short, everything was 
>> going fine and I had my parser working 'til I remembered that I 
>> needed to completely ignore all preprocessor directives.  Well.. 
>> I thought that I could tell LEX to toss out all the preprocessor
>> directives, much the same way I was discarding comments:
>> 
>> 	\{[^\n\}]*\}?		{ ; /* Toss out comments */ }
>> 
>> The problem here is that (as you'll note) this expression cannot cope with
>> comments that contain newlines (which is fine, since neither can the
>> compiler 8^), and for the LIFE of me, I CANNOT write an expression
>> that WILL accept similar preprocessor directives that NEED to contain
>> newlines.  In short, I need to nuke lines that have "??" as the first
>> non-white  character of a line, and ending somewhere down the code 
>> a bit with another matching "??".  I've tried things similar to:
>> 
>> 
>
>   What I've done in simuliar situations is to detect the first "??"  then
>call a routine to scan to the next "??".  Here's an example :

  Why don't you just use a start condition?  This is exactly the sort of thing
they are great at.  Just do this.

%START COMMENT
%%
<COMMENT>"?"?"		BEGIN 0;
<COMMENT>.		;
"?"?"			BEGIN COMMENT;
.			ECHO;

-- Mike Garrity
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