Antlr grammar with single quotes doubling as operators.

Question

I am working on an Antlr grammar in which single quotes are used both as operators and in string literals, something like:

operand:     DIGIT | STRINGLIT | reference;
expression:  operand SQUOTE;
STRINGLIT:   '\''  ~('\\'|'\'')* '\'';

Expressions like 1' parse correctly, but when there is input that matches ~('\\'|'\'')* after the quote, such as 1'+2, the lexer attempts to match STRINGLIT and fails. I'd like to be able to recover and emit SQUOTE. Any ideas how to accomplish it?

Thanks.

Answer 1

After testing this grammar a bit in Antlrworks, I think that your problem is that you are being too restrictive here. Antlr would be able to parse 1'+2 if you had a rule that accepted something after it has seen operand SQUOTE. Since ANTLR doesn't know what to do with the +2, it throws an exception.