func String.Tokenize(separator, escape) {
    var buffer = []
    var escaping = false
    for c in this {
        if escaping {
            buffer.Add(c)
            escaping = false
        } else if c == escape {
            escaping = true
        } else if c == separator {
            yield buffer.Flush();
        } else {
            buffer.Add(c);
        }
    }

    if buffer.Length() > 0 || this[this.Length() - 1] == separator {
        yield buffer.Flush()
    }
}

func Array.Flush() {
    var str = String.Concat(values: this)
    this.Clear()
    str
}

let testcase = "one^|uno||three^^^^|four^^^|^cuatro|";
for token in testcase.Tokenize(separator: '|', escape: '^') {
    print(": \(token)")
}