How to implement combination of rules without repeatings in ebnf grammar?

Question

I know that EBNF syntax allows to grab expressions that satisfy one of given options:

(a | b | c)

Is there a similar part of syntax or a workaround that allows to grab expessions that are any combinations of a, b and c without repetitions so that valid expressions would be like:

a b c
b a c
a b
b c
b
none

but not like:

b b c
a a

?

score 2 · Answer 1 · answered Mar 06 '15 at 12:16

2

One way is to spell out the combinations in the rule.

Another way is to use a semantic action that checks for repetitions and raises grako.exceptions.FailedSemantics if it finds them. The parser's behaviour will be just as if the input hadn’t parsed.

answered Mar 06 '15 at 12:16

Apalala

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Thanks for idea of using semantic actions. And how do I implement combinations `with` repetitions? – Sashko Lykhenko Mar 19 '15 at 08:16
You can use ```{a | b | c}+``` (will you upvote/accept the answer?). – Apalala Mar 19 '15 at 12:27

How to implement combination of rules without repeatings in ebnf grammar?

1 Answers1