[antlr-interest] Re: Skipping grammar
Arnar Birgisson
arnarb at oddi.is
Wed Oct 8 01:20:12 PDT 2003
Hello Per,
Perhaps you could make "method {" a single token in the parser, and set
the nestingLevel variable to zero when that one matches.
The solution I posted uses the parser to eat up the stuff inside {...},
another possibility might be to make the lexer do this:
METHOD_BODY
: "method"! '{'! ( BracedExpr | ~'}' )* "};"!
;
protected
BracedExpr
: '{' ( BracedExpr | ~'}' )* "}"
;
Overall, this might be a better solution. The token METHOD_BODY will
then contain as it's text whatever was inside the {...}.
As a side note, this is possible in ANTLR lexers because the are LL(k)
and can thus handle context-free grammars. Conventional lexers are
limited to regular grammars (represented by regular expressions which
are equivalent to finite automata) and can f.x. not match nested braces,
parenthesis etc. See
http://www.antlr.org/doc/lexer.html#Predicated-LL(k)_Lexing for more
information on this.
Arnar
ps. yes, the "i" should have been "nestingLevel" :o)
pps. again, I haven't tried this, it might not even be syntactically
correct
>>> pwolleba at yahoo.no 10/07/03 5:34 PM >>>
Hello again!
I am looking at your example Arnar, and I have some questions.
When I wrote my example I should have included some more information.
The methode node is inside of another node called member (see
example) and it can be more than one!
Member{
Methode {
Sometext;
};
};
This makes your example a bit more difficult to implement, since the
counter will start a zero at the first bracket, which is the member
bracket. I must somehow be able to set nestingLevel = 0 from the
parser when the method node is starting.
How do I do that?
best regards,
Per
Ps: I guess it should be nestingLevel++ instead of i++. Correct?
--- In antlr-interest at yahoogroups.com, "pwolleba" <pwolleba at y...>
wrote:
> Yes that is correct, what is inside the bracket is a different
> language which I at the moment don't want to write a parser for (it
> is pretty complex and big). Anyway I have just come back to work,
and
> I am going to try out your solution Arnar, hopefully it will work!
>
> I just want to thank the community for trying to find a solution to
> my question, and I must say it came really fast!
>
> Best regards,
>
> Per
>
>
> --- In antlr-interest at yahoogroups.com, "Arnar Birgisson"
> <arnarb at o...> wrote:
> > Hi..
> >
> > In my earlier post, I understood Per differently. I think he
want's
> to
> > parse "method name{ <whatever> };" and just eat up <whatever>,
> including
> > any nested braces, and put it in a variable, completely without
> lexing
> > and/or parsing it. Per, is this correct?
> >
> > The result of all this being a tree something like this:
> >
> > METHOD
> > |
> > name-body
> >
> > where the body node contains anything inside the {..} as it's
text.
> >
> > Arnar
> >
> > >>> Anthony.Youngman at E... 10/07/03 1:33 PM >>>
> > I think you're missing the point. Define a ; as SEMI. The way I'd
> do it
> > (and this is all pseudocode) is
> >
> > if_statement: "IF" lcurly (method)* rcurly "ELSE" lcurly (method)*
> > rcurly SEMI ;
> > method: blah_blah SEMI ;
> >
> > That way, the lexer doesn't care whether ; is ending a method or
an
> if
> > clause, and the parser won't get confused because when it hits a
> > right-curly it will be expecting an ELSE or a SEMI, and not a
> method.
> > And if the ELSE is optional you just mark it as such so when the
> parser
> > hits the right-curly after the if, it's expecting an ELSE or a
SEMI
> and
> > nothing else.
> >
> > Cheers,
> > Wol
> >
> > -----Original Message-----
> > From: pwolleba [mailto:pwolleba at y...]
> > Sent: 07 October 2003 08:19
> > To: antlr-interest at yahoogroups.com
> > Subject: [antlr-interest] Skipping grammar
> >
> >
> > I am pretty new to ANTLR so maybe this question is very trivial,
if
> > so even better then maybe it is a simple solution to my problem.
> > Anyway I am struggling with writing a new parser in ANTLR to
> replace
> > and old implementation in Flex/Bison, this to make a product that
> are
> > open for implementation from both C++ as well as Java.
> >
> > The parser will parse a language that we are using to build
> > databases, and it must support this language 100% if to be
> accepted.
> >
> > Here is the code cutting that I am struggling with.
> >
> > method name{
> > SomeText!()text[];
> > if(a < b && b < c){
> > SomeText()!()[];
> > }
> > else{
> > SomeText()!()[];
> > };
> > };
> >
> > I am not interesting in the expression that is inside the name
> > method, I just want ANTLR to grab the text for me, and put it as
a
> > node inside the tree. The problem is the fact that the if/else
> > statement is ending with a "};" which is the same token as the
> method
> > end token, and I have no guarantee that there could be more that
> one
> > inside the method. A solution would be to make a counter that
will
> > increase for each "{" and decrease for each "}", then I would
know
> > when the method ends. To my frustration I don't know how I should
> > make such a counter in ANTRL, that still supports implement in
both
> > Java or C++ code.
> > I would be really really happy if someone could help me with this
> > problem!
> >
> > Best reagards,
> >
> > Per
> >
> >
> >
> >
> >
> > Your use of Yahoo! Groups is subject to
> > http://docs.yahoo.com/info/terms/
> >
> >
> >
> >
> >
> >
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