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From: jimv@radix (Jim Valerio)
Newsgroups: comp.unix.wizards
Subject: Do start conditions work in lex?
Message-ID: <6@radix>
Date: Sat, 19-Sep-87 06:23:52 EDT
Article-I.D.: radix.6
Posted: Sat Sep 19 06:23:52 1987
Date-Received: Sun, 20-Sep-87 22:48:31 EDT
Reply-To: jimv@radix.UUCP (Jim Valerio)
Organization: Radix MicroSystems, Beaverton, Oregon
Lines: 30
Keywords: lex, bug

I've been debugging a problem parsing dates in MH mail, and have narrowed it
down to the point where it looks like lex is not doing the right thing with
start conditions.  I'm having this problem on a System Vr3 80386 system, and
have reproduced the problem on a 4.3bsd Vax system.

Here's a trivial lex file that illustrates the problem I am having:

	%{
	#undef input
	char *inpstr = "01";
	input() { return *inpstr++; }
	yywrap() { return 1; }
	main() { yylex(); }
	%}
	%start Z
	%%
	0 		{ printf("0\n"); BEGIN Z; }
	1		{ printf("shouldn't get here!\n"); }
	<Z>1		{ printf("1\n"); }
	.		{ printf("Error! (%c)\n", yytext[0]); }

When I compile and run this, I get the "shouldn't get here!" message
from processing the the "1" digit in the fixed input string "01".
My understanding of lex leads me to believe that I should instead get
the output lines "0" and then "1".

Am I missing something obvious here, or is there a bug in lex?
If it is a bug, can someone suggest a reasonable workaround?
--
Jim Valerio	{verdix,intelca!mipos3,intel-iwarp.arpa}!omepd!radix!jimv