Update Grammar in Architecture #41
Description
I'm implementing Cucumber Expressions parser in Rust: WIP. And grammar described in the ARCHITECTURE.md really bothers me for couple of reasons.
- Lookbehind and lookahead in
alternationdefinition
EBNF describes context-free grammars and (correct me if I'm wrong) shouldn't have lookaheads and lookbehinds. This also means that described grammar may have non-linear complexity. - Provided grammar describes superset of
Cucumber Expressionsand I don't really see reasons to do it.
So implementing Cucumber Expression parser according to the docs leads to unnecessary performance overhead for no obvious reasons.
Can't we just provide exact grammar for Cucumber Expressions without Note: section?
If I didn't miss anything provided grammar should be exact Cucumber Expressions
cucumber-expression = (alternation
| optional
| parameter
| text)*
text = (- text-to-escape) | ('\', text-to-escape)
text-to-escape = '(' | '{' | '/' | '\'
alternation = single-alternation, ('/', single_alternation)+
single-alternation = ((text-in-alternative+, optional*)
| (optional+, text-in-alternative+))+
text-in-alternative = (- alternative-to-escape) | ('\', alternative-to-escape)
alternative-to-escape = ' ' | '(' | '{' | '/' | '\'
optional = '(', text-in-optional+, ')'
text-in-optional = (- optional-to-escape) | ('\', optional-to-escape)
optional-to-escape = '(' | ')' | '{' | '/' | '\'
parameter = '{', name*, '}'
name = (- name_to_escape) | ('\', name-to-escape)
name-to-escape = '{' | '}' | '(' | '/' | '\'