Re: coupling LALR with a scanner?

Path	csiph.com!x330-a1.tempe.blueboxinc.net!newsfeed.hal-mli.net!feeder3.hal-mli.net!news.lightlink.com!news.iecc.com!lnews.iecc.com!nerds-end
From	Chris Dodd <cdodd@acm.org>
Newsgroups	comp.compilers
Subject	Re: coupling LALR with a scanner?
Date	23 Sep 2011 23:59:35 +0100
Organization	X-Privat.Org NNTP Server - http://www.x-privat.org
Lines	23
Sender	news@iecc.com
Approved	comp.compilers@iecc.com
Message-ID	<11-09-029@comp.compilers> (permalink)
References	<11-07-013@comp.compilers> <11-07-015@comp.compilers> <11-07-018@comp.compilers> <11-08-004@comp.compilers> <11-09-016@comp.compilers> <11-09-017@comp.compilers> <11-09-022@comp.compilers> <11-09-023@comp.compilers>
NNTP-Posting-Host	lnews.iecc.com
X-Trace	gal.iecc.com 1316982586 8817 64.57.183.34 (25 Sep 2011 20:29:46 GMT)
X-Complaints-To	abuse@iecc.com
NNTP-Posting-Date	Sun, 25 Sep 2011 20:29:46 +0000 (UTC)
Keywords	parse, yacc
Posted-Date	25 Sep 2011 16:29:46 EDT
X-submission-address	compilers@iecc.com
X-moderator-address	compilers-request@iecc.com
X-FAQ-and-archives	http://compilers.iecc.com
Xref	x330-a1.tempe.blueboxinc.net comp.compilers:279

Show key headers only | View raw

"Armel" <armelasselin@hotmail.com> wrote in news:11-09-023@comp.compilers:
> Of course in the presence of something like expr / expr the parser knows
> the / is for a division, and if the / is found where expr is expected it
> knows there is a regular expression coming.
> I don't see how I could hack this into a scanner only. maybe some
> specific preceding tokens. I have pass again some time on that question.

The usual way to do this in a flex+bison parser is with a production like:

expr: { beginREGEXP(); } '/' regexp { endREGEXP(); } '/'

where beginREGEXP and endREGEXP are functions in the flex file that set
the start-state into and out of regexp mode.  Note that the actions need
to be BEFORE the parser shifts the '/' token, as an LALR(1) parser may look
ahead one token.  Which means that a '/' must be a '/' regardless of the
scanner state.

Note that if you allow additional lookahead in the parser (LR(k) or LR(*) or
any kind of backtracking) this will break badly.

Chris Dodd
cdodd@acm.org

Back to comp.compilers | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-07-05 01:02 +0200
  Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-07-07 10:28 +0200
    coupling LALR with a scanner? "Karsten Nyblad" <uu3kw29sb7@snkmail.com> - 2011-07-07 10:46 +0200
    Re: coupling LALR with a scanner? "Karsten Nyblad" <uu3kw29sb7@snkmail.com> - 2011-07-08 14:39 +0200
      Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-08-04 11:17 +0200
        Re: coupling LALR with a scanner? Paul B Mann <paul@paulbmann.com> - 2011-09-13 13:38 -0700
          Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-09-16 10:47 +0200
            Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-09-19 13:52 +0200
            Re: coupling LALR with a scanner? Paul B Mann <paul@paulbmann.com> - 2011-09-19 12:12 -0700
              Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-09-20 09:40 +0200
                Re: coupling LALR with a scanner? Chris Dodd <cdodd@acm.org> - 2011-09-23 23:59 +0100
                Re: coupling LALR with a scanner? Chris F Clark <cfc@shell01.TheWorld.com> - 2011-09-29 00:00 -0400
                Re: coupling LALR with a scanner? "Armel" <armelasselin@hotmail.com> - 2011-10-02 16:41 +0200
                Re: coupling LALR with a scanner? Chris F Clark <cfc@shell01.TheWorld.com> - 2011-10-03 11:59 -0400
                Re: coupling LALR with a scanner? glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2011-10-03 21:08 +0000
          Re: coupling LALR with a scanner? Paul B Mann <paul@paulbmann.com> - 2011-09-17 10:38 -0700

csiph-web