Re: modification of parser.y

• Date: Sat, 22 Jun 1996 21:46:41 PDT
• From:
  hpa@trantor.zytor.com (H. Peter Anvin)
• Reply-To:
  hpa@storm.net (H. Peter Anvin)
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• References: <199606222159.OAA16729@wasteland.calbbs.com> <4qigbi$vsv@terminus.zytor.com>

Followup to:  <4qigbi$vsv@terminus.zytor.com>
By author:    hpa@trantor.zytor.com (H. Peter Anvin)
In newsgroup: local.moo
> >  
> > I would be equally grateful to anyone who could point me to a man page
> > for LALR.  It seems to be conveniently missing on my system, as well as
> > every man pages server I've found on the web.  (ARGH!)
> >  

Oh, by the way... LALR(1) is not a man page... the subset of all
context-free grammars that yacc can generate a parser for is called
LALR(1).  The parsing technique used is called "lookahead LR" (LALR --
LR stands for left shift, right reduction) and yacc supports one (1)
token worth of lookahead.  The one-token lookahead limit is, by the
way, the reason why you wouldn't want to implement a chevron (<<)
operator by entering '<' '<' directly into the parser.

I have occationally seen LALR(2) parser generators, but they tend be
very memory-hungry.  Similarly, an LALR(0) parser is very
memory-efficient; unfortunately too many useful languages aren't in
the LALR(0) set.

For information on how to use yacc I recommend "Lex and Yacc" by
Levine, Mason & Brown, published by O'Reilly and Associates.  The
venerable "dragon book" has a more in-depth discussion of the LALR
parsing techique.

	-hpa

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• Re: modification of parser.y
• From: Berry Kercheval <kerch@parc.xerox.com>

• modification of parser.y
• From: Brian Buchanan <brian@wasteland.calbbs.com>
• Re: modification of parser.y
• From: hpa@trantor.zytor.com (H. Peter Anvin)

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