[antlr-interest] Conditional tree parsing

[Bryan Ewbank]

Try this:
   #(IF_TOKEN t=expression
      ( {t == true}?
         val=expression .
      |
         // expression was false
         . val=expression
      )
   )

This uses the value of the expression, captured in t, to direct the parse to
only evaluate the leg of interest.

Hope this helps,
- Bryan

On 10/31/06, VAUCHER Laurent <VAUCHER at fermat.eu> wrote:
> I'm currently implementing an expression evaluator as a TreeParser, so, for
> correct evaluation semantic, I need to conditionnally evaluate some parts of
> the parse tree...
>
> When evaluating, I need to direct the tree parser to only walk the correct
> branch of the tree (expr1AST is testexpr is true, expr2Ast otherwise).
>
>   My first try was to write:
>
> #(IF_TOKEN t=expression v1=expression v2=expression)
>   but then both expression are evaluated (wrong!)