[antlr-interest] Re: Skipping grammar
pwolleba
pwolleba at yahoo.no
Wed Oct 8 02:12:58 PDT 2003
Hello again
Thanks for helping me out Arnar, your solutions are really good!
Still I think I will have problem implementing them, much because I
have not given you enough information.
I need to make a method tag in my tree that contains information,
such as arguments into the method and such (see example).
Method testMethod (Args,Args
.){
Expression text
}
method
|
|--------Name
|
|--------Arguments
|
|-------- Expression
If I solve this in my lexer I will not be able to create this node
tree, it will just be one node method that contains all the text. If
I drop the "method"tag in my METHOD_BODY tag, it will trigger at all
the other bracket in my document.
Can I somehow make my lexer rule without the "method" tag, and then
make it just trigger when I need the method body?
best regards,
Per
--- In antlr-interest at yahoogroups.com, "Arnar Birgisson"
<arnarb at o...> wrote:
> 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 y... 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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