[antlr-interest] how to let parser control lexer state.

[femtowin1]

Hi all, in antlr3, can parser control lexer state
and decide how lexer lexing? some grammar has ambiguity
decided upon by parser knowledge.
  for ruby grammar <<
x << 1
test
1
if x is a variable, then << is shift operator,
otherwise it is a heredoc. so lexing must know
from the symbol table whether x has been defined
beforehand. But current antlrv3 implementation,
lexer lexing to a constant token stream, and feed
it into parser, so can't achieve this effect.
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