Why can’t flex understand this variable trailing context pattern?
To: Gregory Margo <firstname.lastname@example.org>
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 <vern>
> Enclosed is a lex file that "real" lex will process, but I cannot get
> 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 "(a/b)+". So the solution is to remove the
parentheses. Note that you must also be building the scanner with the -l
option for AT&T lex compatibility. Without this option, flex automatically
encloses the definitions in parentheses.