CODEWITHSUNDEEP
antlrantlr4
Ken Homer
Ken Homer

Reputation: 141

Is there a way to get the number of tokens in an ANTLR4 parser rule?

In ANTLR4, it seems that predicates can only be placed at the front of sub-rules in order for them to cause the sub-rule to be skipped. In my grammar, some predicates depend on a token that appears near the end of the sub-rule, with one or more rule invocations in front of it. For example:

date :
    {isYear(_input.LT(3).getText())}?
        month  day=INTEGER  year=INTEGER     { ... }

In this particular example, I know that month is always one single token, so it is always Token 3 that needs to be checked by isYear(). In general, though, I won't know the number of tokens making up a rule like month until runtime. Is there a way to get its token count?

Upvotes: 1

Views: 978

Answers (1)

Sam Harwell
Sam Harwell

Reputation: 100069

There is no built-in way to get the length of the rule programmatically. You could use the documentation for ATNState in combination with the _ATN field in your parser to calculate all paths through a rule - if all paths through the rule contain the same number of tokens the you have calculated the exact number of tokens used by the rule.

Upvotes: 1

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