local function reverse(a, s, e)
    for i = s, e / 2 do
        local counter_i = e - (i - 1)
        local tmp = a[i]
        a[i] = a[counter_i]
        a[counter_i] = tmp
    end
end

local a = {5, 3, 8, 1}
reverse(a, 1, #a)
print(table.unpack(a))