func insert(tracks: [Track], track: Track, isGreater: (a: Track, b: Track) -> Bool?) -> Int {
    var high: Int = tracks.count - 1
    var low: Int = 0
    var index: Int
    while (true) {
        index = (high - low) / 2
        if (high - low) < 2 {
            return index
        }
        print(index)
        let result = isGreater(a: track, b: tracks[index])
        if result == true {
            low = index + 1
        }
        else if result == false {
            high = index - 1
        }
        else {
            return index
        }
    }
}