p6.p6

grammar GrammarAdvice {
    rule TOP {
        :my $*USE-WS = 0;
        "use" <type> "for" <significance> "whitespace"
    }
    token type {
        | "tokens" { $*USE-WS = 0 }
        | "regex"  { $*USE-WS = 0 }
        | "rules"  { $*USE-WS = 1 }
    }
    token significance {
        | <?{ $*USE-WS == 0 }> "insignificant"
        | <?{ $*USE-WS == 1 }> "significant"
    }
}

say GrammarAdvice.parse("use rules for insignificant whitespace");
say GrammarAdvice.parse("use tokens for insignificant whitespace");
say GrammarAdvice.parse("use regex for insignificant whitespace");
say GrammarAdvice.parse("use rules for significant whitespace");
say GrammarAdvice.parse("use tokens for significant whitespace");
say GrammarAdvice.parse("use regex for significant whitespace");