[antlr-interest] Re: Using multiple parsers -- newbie question

[Matt Benson]

I think the answer would be to put the common parts of
the parser grammar in a base parser and extend that. 
You could declare all the rules of the base parser
class to be protected just for peace of mind, as well.

-Matt

--- biz_morland <biz_morland at yahoo.com> wrote:
> Hi all,
> 
> The parser I'm developing is part of a calculator
> program that 
> analyzes text like: 2+3^3 and contains rules that
> determine the order 
> in which an expression is parsed --> (2+3)^3 or
> 2+(3^3) .
> 
> I had to create two different parsers because the
> rules may differ 
> slightly depending on the "mode" the calculator may
> be in. I 
> emphasize "slightly" because both parsers are 95%
> the same, they 
> differ in just a single rule.
> 
> I noticed that no matter which parser was called by
> the "if" 
> statement in my Java program (that is, no matter
> which mode my 
> calculator was in), the above expression would
> always be parsed just 
> one way regardless of mode. I had each parser in its
> own grammar 
> file. It seemed that the parser that was preferred
> by the program 
> only depended on which grammar file I _last_
> saved/compiled. Having 
> an "if" statement in the Java program seemed to make
> no difference.
> 
> Out of desperation I followed the "bad" way, which
> seems like a blunt 
> way of fixing the problem. But it worked so I can't
> complain. However 
> the second way seems interesting, if I have time at
> the end of this 
> project I will try to implement it. I'll probably
> have to do some 
> extra reading about the commands you mentioned. But
> at least it now 
> seems possible to implement 2 or more parsers.
> 
> Thanks!
> Greg
> 
> --- In antlr-interest at yahoogroups.com, "antlrlist"
> <antlrlist at y...> 
> wrote:
> > 
> > Hello Greg,
> > 
> > You didn't mention the difference between
> ExpressionParser_1 and 
> > ExpressionParser_2 nor how did you detected that
> "both analizers 
> > where the same".
> > 
> > However I see where your problem might be: you
> might be having 
> > problems with token vocabularies if
> ExpressionParser_1 or 
> > ExpressionParser_2 define tokens in the token
> section or if they 
> have 
> > unnamed tokens (they have strings in the rules,
> like 
> > while: "while" ... ;).
> > 
> > There are two ways of solving this: a bad one and
> a good one.
> > 
> > The bad one consists in renaming your lexers and
> treeparsers, so 
> > you'd get
> >  - "expression_1.g" containing:
> ExpressionParser_1, 
> > ExpressionLexer_1, and  ExpressionTreeWalker_1.
> >  - "expression_2.g" contains: ExpressionParser_2,
> ExpressionLexer_2 
> > and ExpressionTreeWalker_2.
> > 
> > This solution won't probably match your needs, so
> you'll have to 
> > implement the "good one".
> > <p>
> > The good one consists on defining each analizer in
> one separated 
> > file, and using grammar inheritance in the
> parsers. So you'd get:
> >  - "expressionLexer.g" containing ExpressionLexer
> >  - "expressionParser1.g" containing
> ExpressionParser1
> >  - "expressionParser2.g" containing
> ExpressionParser2
> >  - "expressionTreeParser.g" containing
> ExpressionTreeParser
> > <p>
> > When you write a set of analyzers in the same
> file, ANTLR deals 
> with 
> > vocabulary sharing authomatically. If you write
> them in separate 
> > files, you'll have to share vocabularies manually
> (see "Token 
> > vocabularies" on antlr docs).
> > <p>
> > In order to do this, you must:
> >  - Copy/paste each analizer's definition in each
> grammar file.
> >  - The lexer should need to export its vocabulary
> with the 
> > exportVocab option. Give the vocab a name like
> "lexer" 
> > (exportVocab=lexer;).
> >  - In ExpressionParser1 you shoud importVocab the
> Lexer's 
> vocabulary 
> > (importVocab=lexer;)and exportVocab the new
> vocabulary 
> > (exportVocab=parser1;).
> >  - ExpressionParser2 should be defined as a
> derived grammar of 
> > ExpressionParser1. This is, instead of being
> "class 
> ExpressionParser2 
> > extends Parser" it will be declared like "class
> ExpressionParser2 
> > extends ExpressionParser1". You'll also have to
> compile 
> > expressionParser2.g with the command line "java
> antlr.Tool -glib 
> > expressionParser1.g expressionParser2.g" (see
> "grammar inheritance" 
> > on the docs). Grammar inheritance allows you to
> "import" the rules 
> of 
> > ExpParser1 in ExpParser2, so you only have to
> write the ones that 
> > change.
> >  - ExpressionParser2 should import the vocab of
> *ExpressionParser1* 
> > (importVocab=parser1;) and export its own vocab 
> exportVocab=parser2;).
> >  - ExpressionTreeParser should import
> ExpressionParser2's vocab 
> > (importVocab=parser2).
> > 
> > Tell me if this helps you
> > 
> > Enrique
> > 
> > --- In antlr-interest at yahoogroups.com,
> mzukowski at y... wrote:
> > > I'd say try to step through it with a debugger. 
> I don't see any 
> > obvious
> > > clues here.
> > > 
> > > Monty
> > > 
> > > -----Original Message-----
> > > From: biz_morland [mailto:biz_morland at y...] 
> > > Sent: Wednesday, June 11, 2003 2:46 PM
> > > To: antlr-interest at yahoogroups.com
> > > Subject: [antlr-interest] Using multiple parsers
> -- newbie 
> question
> > > 
> > > 
> > > Hi,
> > > 
> > > I've written a Java program that uses an
> ExpressionParser, 
> > > ExpressionLexer, and ExpressionTreeWalker. I've
> put these three 
> > > classes in a separate grammar file called
> expression.g and 
> > compiling 
> > > and running these class doesn't produce any
> problems.
> > > 
> > > Now I've discovered an extra requirement which
> basically means I 
> > have 
> > > to create 2 parsers, each only slightly
> different in the way they 
> > > parse some text. 
> > > 
> > > So now I have to write two separate classes:
> ExpressionParser_1 
> and 
> > > ExpressionParser_2. (The other classes,
> ExpressionLexer and 
> > > ExpressionTreeWalker, should stay exactly the
> same.)
> > > 
> > > My question is, how does one implement two
> different parsers?
> > > 
> 
=== message truncated ===


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