ANTLR 3.x - How to format rewrite rules

Question

I'm finding myself challenged on how to properly format rewrite rules when certain conditions occur in the original rule.

What is the appropriate way to rewrite this:

unaryExpression: op=('!' | '-') t=term
  -> ^(UNARY_EXPR $op $t)

Antlr doesn't seem to like me branding anything in parenthesis with a label and "op=" fails. Also, I've tried:

unaryExpression: ('!' | '-') t=term
  -> ^(UNARY_EXPR ('!' | '-') $t)

Antlr doesn't like the or '|' and throws a grammar error.

Replacing the character class with a token name does solve this problem, however it creates a quagmire of other issues with my grammar.

--- edit ----

A second problem has been added. Please help me format this rule with tree grammar:

multExpression : unaryExpression (MULT_OP unaryExpression)* ;

Pretty simple: My expectation is to enclose every matched token in a parent (imaginary) token MULT so that I end up with something like:

 MULT
  o
  |
  o---o---o---o---o
  |   |   |   |   |
 '3' '*' '6' '%'  2

Answer 1

unaryExpression
    :    (op='!' | op='-') term
         -> ^(UNARY_EXPR[$op] $op term)
    ;

I used the UNARY_EXPR[$op] so the root node gets some useful line/column information instead of defaulting to -1.