[antlr-interest] "context sensitivity" of tree parsing

[Benjamin Shropshire]

I known context sensitive has another manging but it is the most 
descriptive term here:

I have a tree parser working over an AST and I have a particular rule 
that gets used in 2 places. In one place I want it to do something and 
in another I don't want it to do anything. Rather than copy the whole 
rule (and potentially a pile of referenced rules) and edit out the 
actions, my first though is to pass a bool in to test on (on true I'm in 
the one cases, on false I'm in the other) but this seems a bit clunky.

Is there a better way? If so, what is it called and where can I read up 
on it?