[antlr-interest] disambiguating semantic predicates

[Tom Smith]

I am trying to use disambiguating semantic predicates, as I have a
case where "a property of a token must dictate how the parser
interprets it" (to quote The Definitive ANTLR Reference, p. 287).  A
snippet of the grammar looks like:

event
    :
    ^(EVENT T1 messageExp (h=hostcode)?)
    |
    ^(EVENT T2 TIMEOUT (h=hostcode)?)
    |
    ^(EVENT T3 varName (h=hostcode)?)
    ;

T1
    :
    { isTypeT1(((Tree) input.LT(1)).getText()) }?
    varName
    ;

T2
    :
    { isTypeT2(((Tree) input.LT(1)).getText()) }?
    varName
    ;

T3
    :
    { isTypeT3(((Tree) input.LT(1)).getText()) }?
    varName
    ;

varName