  void make_grammar() {
    // Setup PEG syntax parser
    g["Grammar"] <= seq(g["Spacing"], oom(g["Definition"]), g["EndOfFile"]);
    g["Definition"] <=
        cho(seq(g["Ignore"], g["IdentCont"], g["Parameters"], g["LEFTARROW"],
                g["Expression"], opt(g["Instruction"])),
            seq(g["Ignore"], g["Identifier"], g["LEFTARROW"], g["Expression"],
                opt(g["Instruction"])));
    g["Expression"] <= seq(g["Sequence"], zom(seq(g["SLASH"], g["Sequence"])));
    g["Sequence"] <= zom(g["Prefix"]);
    g["Prefix"] <= seq(opt(cho(g["AND"], g["NOT"])), g["Suffix"]);
    g["Suffix"] <= seq(g["Primary"], opt(g["Loop"]));
    g["Loop"] <= cho(g["QUESTION"], g["STAR"], g["PLUS"], g["Repetition"]);
    g["Primary"] <=
        cho(seq(g["Ignore"], g["IdentCont"], g["Arguments"],
                npd(g["LEFTARROW"])),
            seq(g["Ignore"], g["Identifier"],
                npd(seq(opt(g["Parameters"]), g["LEFTARROW"]))),
            seq(g["OPEN"], g["Expression"], g["CLOSE"]),
            seq(g["BeginTok"], g["Expression"], g["EndTok"]),
            seq(g["BeginCapScope"], g["Expression"], g["EndCapScope"]),
            seq(g["BeginCap"], g["Expression"], g["EndCap"]), g["BackRef"],
            g["LiteralI"], g["Dictionary"], g["Literal"], g["NegatedClass"],
            g["Class"], g["DOT"]);

    g["Identifier"] <= seq(g["IdentCont"], g["Spacing"]);
    g["IdentCont"] <= seq(g["IdentStart"], zom(g["IdentRest"]));

    const static std::vector<std::pair<char32_t, char32_t>> range = {
        {0x0080, 0xFFFF}};
    g["IdentStart"] <= cho(cls("a-zA-Z_%"), cls(range));

    g["IdentRest"] <= cho(g["IdentStart"], cls("0-9"));

    g["Dictionary"] <= seq(g["LiteralD"], oom(seq(g["PIPE"], g["LiteralD"])));

    auto lit_ope = cho(seq(cls("'"), tok(zom(seq(npd(cls("'")), g["Char"]))),
                           cls("'"), g["Spacing"]),
                       seq(cls("\""), tok(zom(seq(npd(cls("\"")), g["Char"]))),
                           cls("\""), g["Spacing"]));
    g["Literal"] <= lit_ope;
    g["LiteralD"] <= lit_ope;

    g["LiteralI"] <=
        cho(seq(cls("'"), tok(zom(seq(npd(cls("'")), g["Char"]))), lit("'i"),
                g["Spacing"]),
            seq(cls("\""), tok(zom(seq(npd(cls("\"")), g["Char"]))), lit("\"i"),
                g["Spacing"]));

    // NOTE: The original Brian Ford's paper uses 'zom' instead of 'oom'.
    g["Class"] <= seq(chr('['), npd(chr('^')),
                      tok(oom(seq(npd(chr(']')), g["Range"]))), chr(']'),
                      g["Spacing"]);
    g["NegatedClass"] <= seq(lit("[^"),
                             tok(oom(seq(npd(chr(']')), g["Range"]))), chr(']'),
                             g["Spacing"]);

    g["Range"] <= cho(seq(g["Char"], chr('-'), g["Char"]), g["Char"]);
    g["Char"] <= cho(seq(chr('\\'), cls("nrt'\"[]\\^")),
                     seq(chr('\\'), cls("0-3"), cls("0-7"), cls("0-7")),
                     seq(chr('\\'), cls("0-7"), opt(cls("0-7"))),
                     seq(lit("\\x"), cls("0-9a-fA-F"), opt(cls("0-9a-fA-F"))),
                     seq(lit("\\u"), cls("0-9a-fA-F"), cls("0-9a-fA-F"),
                         cls("0-9a-fA-F"), cls("0-9a-fA-F")),
                     seq(npd(chr('\\')), dot()));

    g["Repetition"] <=
        seq(g["BeginBlacket"], g["RepetitionRange"], g["EndBlacket"]);
    g["RepetitionRange"] <= cho(seq(g["Number"], g["COMMA"], g["Number"]),
                                seq(g["Number"], g["COMMA"]), g["Number"],
                                seq(g["COMMA"], g["Number"]));
    g["Number"] <= seq(oom(cls("0-9")), g["Spacing"]);

    g["LEFTARROW"] <=
        seq(cho(lit("<-"), lit(reinterpret_cast<const char *>(u8"←"))),
            g["Spacing"]);
    ~g["SLASH"] <= seq(chr('/'), g["Spacing"]);
    ~g["PIPE"] <= seq(chr('|'), g["Spacing"]);
    g["AND"] <= seq(chr('&'), g["Spacing"]);
    g["NOT"] <= seq(chr('!'), g["Spacing"]);
    g["QUESTION"] <= seq(chr('?'), g["Spacing"]);
    g["STAR"] <= seq(chr('*'), g["Spacing"]);
    g["PLUS"] <= seq(chr('+'), g["Spacing"]);
    ~g["OPEN"] <= seq(chr('('), g["Spacing"]);
    ~g["CLOSE"] <= seq(chr(')'), g["Spacing"]);
    g["DOT"] <= seq(chr('.'), g["Spacing"]);

    ~g["Spacing"] <= zom(cho(g["Space"], g["Comment"]));
    g["Comment"] <=
        seq(chr('#'), zom(seq(npd(g["EndOfLine"]), dot())), g["EndOfLine"]);
    g["Space"] <= cho(chr(' '), chr('\t'), g["EndOfLine"]);
    g["EndOfLine"] <= cho(lit("\r\n"), chr('\n'), chr('\r'));
    g["EndOfFile"] <= npd(dot());

    ~g["BeginTok"] <= seq(chr('<'), g["Spacing"]);
    ~g["EndTok"] <= seq(chr('>'), g["Spacing"]);

    ~g["BeginCapScope"] <= seq(chr('$'), chr('('), g["Spacing"]);
    ~g["EndCapScope"] <= seq(chr(')'), g["Spacing"]);

    g["BeginCap"] <= seq(chr('$'), tok(g["IdentCont"]), chr('<'), g["Spacing"]);
    ~g["EndCap"] <= seq(chr('>'), g["Spacing"]);

    g["BackRef"] <= seq(chr('$'), tok(g["IdentCont"]), g["Spacing"]);

    g["IGNORE"] <= chr('~');

    g["Ignore"] <= opt(g["IGNORE"]);
    g["Parameters"] <= seq(g["OPEN"], g["Identifier"],
                           zom(seq(g["COMMA"], g["Identifier"])), g["CLOSE"]);
    g["Arguments"] <= seq(g["OPEN"], g["Expression"],
                          zom(seq(g["COMMA"], g["Expression"])), g["CLOSE"]);
    ~g["COMMA"] <= seq(chr(','), g["Spacing"]);

    // Instruction grammars
    g["Instruction"] <=
        seq(g["BeginBlacket"], cho(g["PrecedenceClimbing"]), g["EndBlacket"]);

    ~g["SpacesZom"] <= zom(g["Space"]);
    ~g["SpacesOom"] <= oom(g["Space"]);
    ~g["BeginBlacket"] <= seq(chr('{'), g["Spacing"]);
    ~g["EndBlacket"] <= seq(chr('}'), g["Spacing"]);

    // PrecedenceClimbing instruction
    g["PrecedenceClimbing"] <=
        seq(lit("precedence"), g["SpacesZom"], g["PrecedenceInfo"],
            zom(seq(g["SpacesOom"], g["PrecedenceInfo"])), g["SpacesZom"]);
    g["PrecedenceInfo"] <=
        seq(g["PrecedenceAssoc"],
            oom(seq(ign(g["SpacesOom"]), g["PrecedenceOpe"])));
    g["PrecedenceOpe"] <=
        tok(oom(
            seq(npd(cho(g["PrecedenceAssoc"], g["Space"], chr('}'))), dot())));
    g["PrecedenceAssoc"] <= cls("LR");

    // Set definition names
    for (auto &x : g) {
      x.second.name = x.first;
    }
  }
Unknown