[antlr-interest] tree rewriting - change not propagating upwards

[Michael Bedward]

Hi folks,

I have a grammar to rewrite an AST, most of which works wonderfully
well. But one bit has had me pulling what remains of my hair out...

The relevant excerpts are:

expr         : ^(FUNC_CALL id=ID expr_list)
                  -> {isPosFunc($id.text)}?
IMAGE_POS_LOOKUP[getProxyVar($id.text)]
                  -> {isInfoFunc($id.text)}?
IMAGE_INFO_LOOKUP[getProxyVar($id.text)]
                  -> ^(FUNC_CALL ID expr_list)

                | var

                |  ...other stuff...
                ;

expr_list    : ^(EXPR_LIST expr*)
                ;

var             :ID
                  -> {isPosVar($ID.text)}? POS_VAR[$ID.text]
                  -> {isImageVar($ID.text)}? IMAGE_VAR[$ID.text]
                  -> {isLocalVar($ID.text)}? LOCAL_VAR[$ID.text]
                  -> {isJiffleConstant($ID.text)}? CONSTANT[$ID.text]
                  -> NON_LOCAL_VAR[$ID.text]
                ;

The "var" rule categorizes an ID token, using some helper methods, and
rewrites it as a specific token type.  This works fine for most
expressions but doesn't seem to work when the expression (expr) is an
element in an expression list (expr_list) used with function calls.

When I follow the generated Java code in the debugger the rewriting
from ID to CONSTANT (for example) works. When the parser moves back up
to the expr_list rule the rewritten token is still visible. However,
when I get back to the FUNC_CALL branch of the expr rule the rewritten
token has been lost and there is just the original ID token type.

I know this will be something stupid and obvious and trivial but I
just can't spot it. Any tips would be much appreciated.

I'm using ANTLR 3.2, Java target.

cheers
Michael