[antlr-interest] Skipping sections of the input stream

[Burton Samograd]

I figured out a way to do what I was thinking using a chunk of code like so:

sectiona: SECTIONA name {
       if ($name.text->chars != expectedName) {
                      // consumeUntilSet for SECTIONA || SECTIONB
                      // throw SKIP_SECTION_EXCEPTION
      }
    }  LCURLY subsectiona* RCURLY -> ...
     ;
    [ SKIP_SECTION_EXCEPTION] {
        PSRSTATE->error = ANTLR3_FALSE;
        PSRSTATE->failed = ANTLR3_FALSE;
    }

Sent to the list  for future reference.

--
Burton Samograd

-----Original Message-----
From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-bounces at antlr.org] On Behalf Of Burton Samograd
Sent: Thursday, June 28, 2012 10:34 AM
To: Mike Lischke
Cc: antlr-interest at antlr.org
Subject: Re: [antlr-interest] Skipping sections of the input stream

I simplified my example and we actually have two top level section types which I think would greatly Increase the complexity of a splitter and require making a baby parser to parse quite a bit of the input structure before passing it to the actual parser.


Not an impossible task, but I think if it could be done completely in the grammar using the standard input stream it wouldn't create such a dependency between the baby parser and the actual parser unless you can suggest a better way to do the splitting.

--
Burton Samograd

-----Original Message-----
From: Mike Lischke [mailto:mike at lischke-online.de]
Sent: Thursday, June 28, 2012 10:27 AM
To: Burton Samograd
Subject: Re: [antlr-interest] Skipping sections of the input stream


Burton,

> It has been requested that we only parse the section that has been
> specified by the user.  I am thinking that a strategy where we have a rule like:
>
> section: SECTION quoted_string {
>    // if quoted_string != requested_section
>    // skip entire section by matching { and } parens
>    }
>    | SECTION quoted_string LCURLY subsection* RCURLY -> ...
>    ;
>
> First off, is what I would like to do possible and is my approach
> reasonable using anltr?  If it is, can I skip over and discard large sections of the input stream like I have outlined above?


It might simplify things a lot (and make it much faster) if you would run your input through a splitter, which takes out anything unwanted and only feed the relevant text to the parser. Skipping over some text considering quotes etc. is simple stuff and can be extremely fast in a (relatively) simple loop.

Mike
--
www.soft-gems.net



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