[antlr-interest] backtrack=false and AST generation

Mark Wright markwright at internode.on.net
Sun Apr 18 05:07:19 PDT 2010


You can pass trees from one rule to another as a parameter(s),
maybe that might help, something like (probably requires more
work to obtain the tree you are after):

protected
expression
    :	e=conditionalOrExpression conditionalExpression[$e.tree]
    ;

protected
conditionalExpression[CommonTree TheActualASTRoot]
    :	QMARK t=expression COMMA f=expression
            -> ^(ITE ${TheActualASTRoot} $t $f)
    |
    ;

Regards, Mark

On Sun, Apr 18, 2010 at 12:39:23PM +0200, Giampaolo Tomassoni wrote:
> Hello everybody,
> 
> I'm facing a problem for which it seems I can't find a reply in the site
> docs and faqs.
> 
> I would like to parse text based on a very simple grammar (arithmetic
> expressions with some boolean enhancement). Every example in the site seems
> to adopt a non-LLR notation, while I would instead prefer to use
> backtrack=false.
> 
> In example, I have stuff like this:
> 
> 
> protected
> expression
>     :	(e=conditionalOrExpression -> $e) c=conditionalExpression
>     ;
> 
> protected
> conditionalExpression
>     :	QMARK t=expression COMMA f=expression	-> ???
>     |
>     ;
> 
> 
> Where conditionalExpression should possibly substitute the AST element
> produced by "expression" with something like
> 
> 	-> ^(ITE [TheActualASTRoot] $t $f)
> 
> in case the first case is matched.
> 
> The fact is that I can't find in the site docs how to replace the top of a
> parent rule, if at all possible.
> 
> Am I completely headed toward the wrong direction?
> 
> Giampaolo
> 
> 
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