Re: lexical analysis question

Mats Kindahl <matkin@acm.org>
30 Mar 2003 21:23:56 -0500

          From comp.compilers
Related articles
lexical analysis question dreder1ck@hotmail.com (2003-03-30)
Re: lexical analysis question matkin@acm.org (Mats Kindahl) (2003-03-30)
Re: lexical analysis question cfc@world.std.com (Chris F Clark) (2003-03-30)
Re: lexical analysis question dreder1ck@hotmail.com (2003-04-05)
| List of all articles for this month |
From: Mats Kindahl <matkin@acm.org>
Newsgroups: comp.compilers
Date: 30 Mar 2003 21:23:56 -0500
Organization: Telia Internet
References: 03-03-178
Keywords: lex
Posted-Date: 30 Mar 2003 21:23:55 EST

dreder1ck@hotmail.com (Drederick) writes:


[snip]
> [Unless you use the fairly disreputable trailing context feature, lex
> doesn't look ahead at all. It makes a DFA which matches the union of
> all of the input patterns, and keeps finding the longest match of the
> input string. -John]


You need lookahead to match the longest match of an input string.
Consider the regular expression "[a-z]*foobar" (which does not contain
a trailing context pattern) and the input string
"xxxfoobaryyyyyyyfooba" (note the missing "r" last); you have to read
the suffix "yyyyyyyfooba" before you can decide that the longest match
is "xxxfoobar".


Regards,
Mats Kindahl
--
IAR Systems in Uppsala, Sweden.


Any opinions expressed are my own and not those of my company.

Post a followup to this message

Return to the comp.compilers page.
Search the comp.compilers archives again.