CODEWITHSUNDEEP
antlr4
hendryau
hendryau

Reputation: 456

Unordered Sub-Productions in ANTLR4

I want to specify a production in ANTLR where the order of its sub-productions does not matter. Note that I want each of the sub-productions to occur once. The brute force way to accomplish this would look something like this:

grammar Foo;

r : (A B) | (B A) ;

A : 'a' ;
B : 'b' ;

As more sub-productions are added, the number of permutations increases... n!/(n-k)!

grammar Foo2;

r : (A B C) | (A C B) | (B A C) | (B C A) | (C A B) | (C B A) ;

A : 'a' ;
B : 'b' ;
C : 'c' ;

Obviously the above solution is not practical. Is there a construct in ANTLR which describes permutations like this in a more concise way?

Upvotes: 3

Views: 184

Answers (1)

Bart Kiers
Bart Kiers

Reputation: 170278

No, there is no way to describe a permutation in a production in ANTLR. You will need to match A, B or C three times and then use a listener to check if all three tokens have been matched exactly one time.

You could do it inside your grammar using custom code and a predicate, but that would make your grammar very hard to read: best do this with a listener.

Upvotes: 6

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