Talk:LALR parser

message: Talk moved; was originally on head page.
((This is rubbish, I will try to write something at the weekend (2001-08-18).  --drj.  Immediate issues: LALR is an algorithm for generating tables for a table driven LR shift reduce parser.  It is not a parser (ooh except maybe the Natural Language community think it is).  pretty sure the derivation of each of the letters is wrong.))
Hmmm. Looking at an old copy of the Dragon Book (which I've heard is pretty well respected in the field, but I may be wrong):
:"These parsers are called LR parsers because they scan the input from left-to-right and construct a rightmost derivation in reverse ... The third method, called lookahead LR (LALR for short) ... the LALR parser of Fig. 6.13 ..." -- Principles of Compiler Design, Aho and Ullman
So there's some precedent for calling something an "LALR parser" since they did it throughout the book and there are five citations, some of them multi-page, in the index for that phrase.  I didn't create the initial entry, but I was kinda irked at the tone of the comment --loh
Okay.  I am intending to use my Dragon Book when I write the article so no doubt I would've found all this out anyway.  "Recursing on the rightmost non-terminal in any grammar rule" is not really a good definition of producins a rightmost derivation BTW.  --drj
Well, I guess my definition was not TOTAL RUBBISH, as drj seemed to imply.
I agree recursing isn't the best way to describe it. Hm.. maybe I should go look at the stuff I said was rubbish and make sure I wasn't wrong.
OK, I looked at my Dragon Book (2nd ed, BTW) and wrote the articles LR parser (which was longish) and LALR parser (which was short).  But my email at home is busted so I can't put it here yet.  *sigh*.  LALR stands for Lookahead LR and is a method for producing LR parsers.  LR stands for Left-to-right scan, Rightmost derivation.  2nd ed Dragon does not use the term LALR parser, and neither do I so I'm not sure what one is;  I assume it is an LR parser produced by the LALR method?  Sorry I used the term "rubbish" because the original entry certainly is not.  --drj
A parser constructed by the LALR technique has tables the size of an LR(0) parser, yet is far more powerful and useful, which I think makes it a legitimate parser classification.  It is also common enough (being produced by YACC) that the classification is useful in practice.  The term "LALR parser" is also unambiguous, and (above all else) is in common usage, and so I think the objection to its use in Wikipedia is somewhat pedantic.  --Doradus 16:33, Sep 17, 2004 (UTC)
Your source material link (to an Oberlin CS lecture) is dead. :( --utopianheaven 11:31, Jan 30, 2006 (UTC)
How about some information on DFA and state transition?  Maybe a comparison to LL and LR parsing techniques?  Niklaus Wirth states (in his book "Compiler Construction", , p. 24) that the "LL" and "LR" naming convention was introduced by Knuth. Might also mention that the "LR" in stands for "L" = "Left-to-Right" and "R" = "Rightmost production", and explain what that means.  BTW, the "Gold", "Anagram", etc., software packages are LALR.  You might want to add some references:  http://www.devincook.com/goldparser/, http://www.parsifalsoft.com/, etc.12.110.196.19 21:26, 7 February 2007 (UTC)
thread_title: Initial comments

message: The article gives some idea of what an LALR parser is (well, this is obvious enough when the acronym is expanded). But LALR(1) and LALR(2) are then mentioned — what are these? 89.217.239.233 (talk) 15:10, 24 December 2010 (UTC)
replies: text: The number in parenthesis is the lookahead. --Allen3 talk 12:50, 8 March 2011 (UTC)
thread_title:  What's LALR(1)? 

message: The article used to read "The original and most widely known parser generator was yacc, developed on the UNIX operating system."  The "LALR Parser Generator" article (LALR_parser_generator) gave dates for XPL as 1970 and yacc as 1975.  I changed the date for XPL there to 1968 to correspond to the original FJCC paper, but in either case yacc is not the "original" unless an earlier date is established, so I deleted this sentence.  I'd accept "most widely known," except that now there are lots, starting with Gnu Bison.
Peter Flass (talk) 19:26, 6 October 2011 (UTC)
replies: text: Are you sure DeRemer wrote an LALR parser generator for his 1969 thesis?  I can't find a reference to that in the dissertation.  --Doradus (talk) 01:15, 2 August 2014 (UTC)
thread_title:  Earliest? 

message: PDA is not a data structure. In addition, I don't like "based on a finite-state-automata concept" in the first sentence.
I suggest for the first two sentences:
"In computer science, an LALR parser (or look-ahead LR parser) is a type of LR parser based on Finite-state machines (FSM). The Model of computation used in the LALR parsers is the pushdown automaton (PDA)."  Ginandi (talk) 12:18, 2 February 2012 (UTC)
thread_title:  PDA is not a data structure 

message: I am making this request because Wikipedia is for public consumption, not just for us compugeeks.  The terminology and the complexity of the sentences in the introduction that a normal person would probably go catatonic trying to figure out what it meant and, if that didn't happen, they'd spend the next 6 years learning all the terminology necessary just to start to understand it.  A bit of hyperbole, actually, but I think you get my point.  PLEASE "dumb down" the explanation for the mere mortals.  Thanks!!!!ReveurGAM (talk) 13:16, 26 February 2012 (UTC)
replies: text: Not a bad idea.  Somehow describe what an LALR parser does rather than what it is (i.e. why would I be interested in this), then get to the technical stuff in a later paragraph.Peter Flass (talk) 13:53, 26 February 2012 (UTC)
thread_title:  Please make the introductory explanation of LALR parser....introductory 

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thread_title:  External links modified 

message: I've always heard it pronounced "laller" rather than "el-ay-el-ar" but it is hard to get a reference for this either way.
198.91.146.14 (talk) 01:43, 10 February 2019 (UTC)
thread_title:  Pronunciation of "LALR"