gistfile1.txt

# use Grammar::Tracer;

grammar G {
    token TOP {^ <integer-constant> $};
    proto token integer-constant {*};
    token integer-constant:sym<8>  { <octal-constant> };
    token integer-constant:sym<10> { <decimal-constant> };
    token integer-constant:sym<16> { <hexadecimal-constant> };
    token octal-constant { '0' <odigit>* };
    token decimal-constant { <nzdigit> <digit>* };
    token hexadecimal-constant { <.hexadecimal-prefix> <xdigit>* };
    token hexadecimal-prefix { '0' <[xX]> };
    token nzdigit { <[1..9]> };
    token odigit { <[0..7]> };
}

say G.parse('0');