[antlr-interest] Re: strings and vocab?
lgcraymer
lgc at mail1.jpl.nasa.gov
Mon Apr 12 17:34:58 PDT 2004
What you would have to do is
SEMI
options { testLiterals = true; }
: ';' ;
in the lexer. The testLiterals flag is tested when deciding whether or not to do a table lookup, and the local option overrides the global
option within the lexer rule.
The ANTLR manual is the specification; we might get around to having a separate spec for ANTLR 3, but I would not count on that.
ANTLR through 2.7.x is public domain; starting with 2.8, it will be under a minimally restrictive open source license.
--Loring
--- In antlr-interest at yahoogroups.com, "idontwantanidwith2000init" <idontwantanidwith2000init at y...> wrote:
> What if I have token that lex ';' in the lexer
> and in the parser ";"
> Will that work?
> Would I get LITERAL_;?
> Moreover, it seems like testLiterals can be set in options and in a
> lexer rule. What is it translated to?
> If I'll specify testLiterals=false in the options and in a specific
> rule I'll set it to true again then it will stay true. Is it so?
> Before debugging it, what does the specification says about it?
> Is there such spec?
> ANTLR is not an open source, right?
>
> Tal.
>
> --- In antlr-interest at yahoogroups.com, "lgcraymer" <lgc at m...> wrote:
> > This one has to be thought of in implementation terms. For any
> lexer rule in which testLiterals is true: tokens are constructed
> and
> > then checked against a hash table of literals. If the table
> contains a corresponding literal definition, then the token type is
> changed to
> > match the literal; if not, it is given the default token type for
> that rule. Note that this is independent of the parser. I believe
> that the
> > current implementation requires that all literals be defined in
> the same file as the lexer grammar.
> >
> > Rules for which testLiterals=false are not checked against the
> hash table. So if you have a rule
> > SEMI : ':' ;
> > and the literal ";" in the parser grammar, you will get strange
> results--the literal ";" has a different token type than the SEMI
> rule; since
> > table lookup does not occur, you will never see the LITERAL_;
> value in the parser.
> >
> > --Loring
> >
> >
> > --- In antlr-interest at yahoogroups.com, ronald.petty at m... wrote:
> > > Alright, I give up :(. What is the secret to Antlr, jk. I am
> still
> > > having some trouble getting started with Antlr, and I believe
> most of my
> > > confusion comes from how strings/tokens/vocab is done.
> > >
> > > I was reading the java.g grammar and was wonding, in the parser
> there is
> > > the rule
> > >
> > > builtInType
> > > : "void"
> > > | "boolean"
> > > | "byte"
> > > ..
> > > ;
> > >
> > > Then in the Lexer there is
> > >
> > > IDENT
> > > options { testLiterals=true; }
> > > : ('a'..'z'|'A'..'Z'|'_'|'$')
> ('a'..'z'|'A'..'Z'|'_'|'0'..'9'|'$')*
> > > ;
> > >
> > > NUM_INT
> > > {boolean isDecimal=false; Token t=null;}
> > > : '.' {_ttype=DOT;}
> > > ( ('0'..'9')+ (EXPONENT)? (f1:FLOAT_SUFFIX
> {t=f1;})?
> > > {
> > > ......
> > >
> > > protected
> > > FLOAT_SUFFIX
> > > : 'f'|'F'|'d'|'D'
> > > ;
> > >
> > >
> > > When the parser says, give me next token (nextToken), the Lexer
> will eat
> > > the next token based on the Lexer rules. Now if the
> string "void" comes
> > > in, the Lexer says, let me check if there is a literal yet for
> this token.
> > > However I do not see what is going on here. The word "void" in
> the
> > > parser may not have been seen yet (calling builtinType). I have
> read teh
> > > vocab document, but still don't think I understand. I have
> tried using
> > > tokens {} and don't understand why that works. Could someone
> explain
> > > these simple concepts? I know I am missing something very
> simple here. I
> > > can follow along the grammars just fine, but I don't understand
> real
> > > workings on these issues, espically how or where you check
> Identifiers vs.
> > > Keywords (I have read a dozen things, and none of them seem to
> explain it
> > > in a way I can follow).
> > >
> > > Also does protected mean that the Lexer will never call
> FLOAT_SUFFIX
> > > directly,if it is trying to get the nextToken, it will only try
> to get it
> > > from the FLOAT_SUFFIX call in NUM_INT. Correct? Is this to
> keep similiar
> > > issues like (IDENT vs Keywords) from happening?
> > >
> > > Thanks Ron
> > >
> > > ps. When I get this all figured out, I will write another
> tutorial
> > > hopefully documenting the same issues I have, maybe help someone
> one day
> > > :)
> > >
> > >
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