func binary_search(a, i) {

    var l = 0
    var h = a.end

    while (l <= h) {
        var mid = (h+l / 2 -> int)
        a[mid] > i && (h = mid-1; next)
        a[mid] < i && (l = mid+1; next)
        return mid
    }

    return -1
}