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From: jwabik@cs.D.UMN.EDU (Jeff Wabik)
Newsgroups: comp.unix.questions
Subject: Any LEX gurus?
Message-ID: <716@umnd-cs.D.UMN.EDU>
Date: Fri, 7-Aug-87 17:09:30 EDT
Article-I.D.: umnd-cs.716
Posted: Fri Aug  7 17:09:30 1987
Date-Received: Sun, 9-Aug-87 05:50:02 EDT
Organization: U. of Minnesota-Duluth, Computer Science
Lines: 46
Keywords: Ack!

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:


	^{WS}*"??"(.|{WS})*"??"

{  Where {WS} is defined as whitespace (i.e. \n, \t, ' ')	}

Which, of course, doesn't work since the (.|{WS})* eats everything to the
end of the file and LEX segment faults..  I've also tried things like:

	^{WS}*"??"[^"??"]"??"

Which in my mind should work, but doesn't..  Arg. My problem is lack of
documentation, since all I've got to work from is the "Compiler Construction
under UNIX" book by Schreiner and Friedman..  Good book, but .. 

Any help would be greatly appreciated and would be responsible for 
retaining a fellow netter's sanity.

Thanks!


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Jeff A. Wabik
University of Minnesota, Duluth  55812

ARPA:	jwabik@cs-gw.d.umn.edu		UUCP:  {umn-cs!umnd-cs-gw!jwabik}

Live long and program.
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