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From: vern%lbl-helios@LBL-RTSG.ARPA (Vern Paxson)
Newsgroups: comp.lang.c
Subject: Re: whats wrong with this lex grammer? (help)
Message-ID: <8709221935.AA01430@lbl-helios>
Date: Tue, 22-Sep-87 15:35:24 EDT
Article-I.D.: lbl-heli.8709221935.AA01430
Posted: Tue Sep 22 15:35:24 1987
Date-Received: Thu, 24-Sep-87 06:27:01 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: vern%lbl-helios.arpa@lbl-rtsg.arpa
Lines: 20

Regarding the lex pattern:

	"(*"([^*]|("*"/[^)]))*"*)"     printf("&%s&\n", yytext);
		      ^
		      |

Lex does not handle trailing context properly inside of ()'s.
Essentially you can only have one instance of trailing context in a
pattern, and it splits the pattern into two halves, the
stuff-to-be-matched and the stuff-that-must-follow.  This limitation is
well rooted in the overall DFA approach lex uses for pattern matching,
so don't expect it to go away.  The limitations mentioned by Esmond
Pitt in comp.unix.wizards (that ^ and $ are not matched inside ()'s)
have a similar origin.

		Vern

	Vern Paxson				vern@lbl-csam.arpa
	Real Time Systems			ucbvax!lbl-csam.arpa!vern
	Lawrence Berkeley Laboratory		(415) 486-6411