Iterative/In-place merge sort for AutoHotkey_L

MergeSort(a)
{
    len := 1
    max := a.MaxIndex()
    loop
    {
        i := 0
        while i < max
        {   ; merge
            l := i + 1
            r := l + len
            i += len << 1
            If (i > max)
                i := max
            while l < r && r <= i
            {
                if a[r] < a[l]
                    a.Insert(l,a.Remove(r++))
                l++
            }
        }
        len <<= 1
    }
    until len >= max
    return a
}