[antlr-interest] Syntactic predicates in lexer

[Loïc Quéran]

Hi,

This is probably a very simple question, but I can't get syntactic
predicates to work in lexer rules:


AssignmentOperatorOrKeywordMarker
  : ':=' => AssignmentOperator
  | ':' => KeywordMarker
  ;

KeywordMarker
  :    ':'
  ;

AssignmentOperator
  :    ':='
  ;

What I want to achieve is to have the lexer produce an assignment operator
':=' token instead of a keyword marker ':' whenever possible.
The error is  "unexpected token: ':='" at AssignmentOperatorOrKeywordMarker
rule definition.

Any help would be welcomed.
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