func binary_search(arr, value, low=0, high=arr.end) {
    high < low && return -1
    var middle = ((high+low) // 2)

    given (arr[middle]) { |item|
        case (value < item) {
            binary_search(arr, value, low, middle-1)
        }
        case (value > item) {
            binary_search(arr, value, middle+1, high)
        }
        case (value == item) {
            middle
        }
    }
}