[antlr-interest] Choosing AST rewrite based on test

[Kirby Bohling]

On Tue, Oct 13, 2009 at 10:39 AM, Bill Andersen
<andersen at ontologyworks.com> wrote:
> Hi All
>
> I have the following rule in a tree grammar (BTW, rewrite = true
> here).  Both AS_TEXT and AS_NAME are imaginary tokens.
>
> text_block
>        : ^(AS_TEXT text_option* name? phrase+ )
>          -> ?????
>        ;
>
> what I want for the ????? part is the rewrite
<snip...>

Bill couldn't you do that "the other way"?  I mean by write a rule like this:

text_block: ^(AS_TEXT text_option* optional_or_gen_name phrase+)
;

optional_or_gen_name:
   (
     name -> ^(NAME_NODE name)
   |
     -> ^(GEN_NAME_NODE)
   )
;

I threw together a quick example that shows the syntax works in a
parser (I'd assume it'd work in a tree grammar).  I think this will
accomplish what you want.  Not sure if you wanted the name to be it's
own subtree, but I generally make rooted trees because it eliminates
backtracking.


Cheers,
    Kirby

// Sample grammar that compiles in ANTLRWorks 1.3 for me.
grammar foo;

options {
rewrite=true;
output=AST;
}

tokens {
NAME;
GEN_NAME;
}

text_block:
	(text_option* name? phrase+ )
	;
	
text_option
	:	 '(' TEXT ')'
	;
	
TEXT:	'a'..'z'
	;

// after GEN_NAME add a { } block to attach the generated name to the token.
gen_or_name
	:	(name -> ^(NAME name) | -> ^(GEN_NAME) )
	;

name:	'{' TEXT '}'
	;
	
phrase
	:	TEXT
	;