[antlr-interest] what does '##' stand for?

[Don Caton]

> -----Original Message-----
> From: antlr-interest-bounces at antlr.org 
> [mailto:antlr-interest-bounces at antlr.org] On Behalf Of Prashant Deva
> Sent: Sunday, March 13, 2005 6:19 AM
> To: antlr-interest at antlr.org
> Subject: [antlr-interest] what does '##' stand for?
> 
> I am not too familiar with tree grammar stuff.
> What does '##' stand for inside an action.
> 
> For example, what does the following rule do -
> 
> grammar
> 	:	headerDef ( classDef )*  EOF!
> 		{ ## = #([GRAMMAR,"grammar"], ##) ; }
> 	;
> 
> PRASHANT
> 

It's shorthand for the tree that the rule returns.  Your example is
equivalent to:

	{ #grammar = #([GRAMMAR,"grammar"], #grammar) ; }

I don't think it's documented anywhere.  It makes actions a bit less verbose
and if you rename the rule, the action won't break.

-- 
Don