func rangex(str) {
    str.split(',').map { |r|
        var m = r.match(/^
            (?(DEFINE) (?<int>[+-]?[0-9]+) )
            (?<from>(?&int))-(?<to>(?&int))
        $/x)
        m ? do {var c = m.ncap; (Num(c{:from}) .. Num(c{:to}))...}
          : Num(r)
    }
}

say rangex('-6,-3--1,3-5,7-11,14,15,17-20').join(',')