func main() {
    let input = "-6,-3--1,3-5,7-11,14,15,17-20"
    print("range: \(input)")
    var r = []
    var last = 0
    for part in input.Split(',') {
        var i = part[1..].IndexOf('-')
        if  i == -1 {
            var n = Integer(part)
            if r.Length() > 0 {
                return print("duplicate value: \(n)") when last == n
                return print("values not ordered: \(last) > \(n)") when last > n
            }
            r.Add(n)
            last = n
        } else {
            var n1 = Integer(part[..i])
            var n2 = Integer(part[(i + 2)..])
            return print("invalid range: \(part)") when n2 < n1 + 2

            if r.Length() > 0 {
                return print("duplicate value: \(n1)") when last == n1
                return print("values not ordered: \(last) > \(n1)") when last > n1
            }

            for i in n1..n2 {
                r.Add(i)
            }
            last = n2
        }
    }

    print("expanded: \(r)")
}

main()