Parser backtracking / greedyness

[cdietrich]

Given a grammar

QUALIFIED_PATH returns string: ID ("." ID)*;
FieldTypeLike:
    'field''<' node=QUALIFIED_PATH '.' field=ID '>';

QUALIFIED_PATH will always eat up the complete FQN on e.g.

field<a.b.Myclass.myfield>

is there a way to tell chevrotain to backtrack?

[msujew]

Hey @cdietrich,

in theory yes, a GATE on the MANY would allow to write a syntactic predicate in order to prevent greedy parsing. However, the current API of Langium doesn't expose this feature of Chevrotain. It's pretty locked down.

In the future I hope to refactor a lot of the parsing mechanism, see also #1742. Exposing more of the existing Chevrotain API is also part of that.

[cdietrich]

ok so that would then required two QUALIFIED_PATH rules. one with a gate that rejects "." ID > and one for other places?

[msujew]

Well, it depends on your use case. But yes, in that you either need two rules, or a parameterized rule.

[cdietrich]

Is there a way to get a chrvrotain rule for a given langium rule ?

[msujew]

As said, it's pretty locked down. See here.