[antlr-interest] [C] Skip sub-tree nodes from AST?

[Jim Idle]

Did you look at the MARK and RELEASE macros?

Jim

> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of Gonzague Reydet
> Sent: Tuesday, January 03, 2012 9:32 AM
> To: antlr-interest at antlr.org
> Subject: [antlr-interest] [C] Skip sub-tree nodes from AST?
>
> Hi all!
>
> It's been two days I am investigating on how to skip a subtree with the
> C target of ANTLR v3.4. I found many discussions on this subject on
> markmail (notably the following one:
> http://markmail.org/message/f5op6tdn4vfpw57v).
> Exactly like this discussion, my original purpose is to implement an
> if/then/else interpreter.
> But I can't find a valid solution to parse only either the "then" or
> the "else" statement skipping the other one and going to the end of the
> if statement after having handled it.
>
> The "if" rule of my parser grammar constructs the AST as following:*
> ^(IF expression ^(THEN statement) ^(ELSE statement?) ENDIF);  *
>
> I have tried two different ways:
> - First using the method proposed in the discussion :
> ^(IF expression {
>     pANTLR3_BASE_TREE n = $IF.getChild($IF, 3);
>     SEEK(n->savedIndex);
>     ...
> } )
> The problem here is the 'savedIndex' field is never set. Is their a way
> for this field to be set before parsing the tree?
>
> - Second using a "wildcard pattern" as following : ^(IF expression
> ^(THEN
> .*) ^(ELSE .*) ENDIF)
> The problem here is the generated tree parser does not handle DOWN
> tokens, so it results in parsing errors when trying to match the
> "wildcarded"
> subtree.
>
>
> I have found the Pie example
> (http://www.antlr.org/wiki/display/ANTLR3/Pie)
> that passes a "defer" parameter to disable execution in all subrules.
> Is this really the only solution for this issue with the C target?
> I would really prefer to use the approach proposed by Terrence for the
> Java target (http://markmail.org/message/7thj4um2bzhuvqpy) but this
> will lead to the same issue of my second solution.
>
> Is there any other solution for this?
>
> Regards,
> Gonzague
>
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