[antlr-interest] header sections (was: Re: ANTLR for Python)

[Marq Kole]

--- In antlr-interest at yahoogroups.com, Ric Klaren <ric.klaren at g...> 
wrote:
> > Now that I have had a look at it, I am beginning to wonder: the 
> > header section seems to be generic, so not tied to either a 
lexer, 
> > parser or treeparser in particular. 
> 
> Think you're right there. Hmmm. I guess you're te first to notice. 
I never
> much needed the sections and always split lexer/parser/treeparser 
so I've
> never run into it myself. Other than a bug in the antlr parser 
with respect
> to them.
>

<SNIP>

> > Alternatively, we can do some clever processing on the named 
header 
> > files (this is just a proposal). If I want a named 
> > section "__init__" - I'm going to the scheme devised for Python 
now -
> >  to be used only for the lexer class, I could provide a 
> > name "<LexerClassName>.__init__" for the header. In the case 
there 
> > is also a parser in the file, that would not get the code in 
this 
> > header section. By using the actual name of the class instead of 
a 
> > name "lexer.__init__" it would even be possible to address this 
> > issue with 2 lexer definitions in the .g file (if that is at all 
> > possible). 
> 
> 2 lexers in one .g is not possible. Your idea will work I guess 
although
> moving some stuff around might be prettier. Hmm might also need 
some fixing
> in antlr.g.

Ric,

Moving things around in the .g files is going to be hard if you do 
not want to break existing code. Maybe that is something to consider 
when doing ANTLR 3.

In the meanwhile, the scheme using named headers that refer to the 
classname works beautifully. I now have an implementation in the 
Python code generator that can handle

header "InstrTreeParser.__init__" {
    // do some treewalker stuff
}

Having defined earlier:

    private static final String initHeaderAction = "__init__";

The simple solution is by replacing the code:

    printHeaderAction(initHeaderAction);

by:

    printHeaderAction(initHeaderAction);
    printHeaderAction(grammar.getClassName() + "." +
                      initHeaderAction);

So in case there is just one grammar per file, you can use 
the "__init__" header, if you have both Lexer and Parser (and/or 
TreeParser) you can use the class-specific "__init__" header. You 
can even use both to provide both shared and specific initialization 
code.

This can be readily translated to any of the code generators for the 
other languages.

Regards,
Marq






 
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