What you wrote is roughly equivalent to this in C:

  {
    const int x = 1;
    {
      const int x = 2;
    }
  }

which is to say, there are two different `x` in there, both immutable, one shadowing the other. You can observe this if you capture the one that is shadowed in a closure:

  iex(1)> x = 1
  1
  iex(2)> f = fn () -> x end
  #Function<43.113135111/0 in :erl_eval.expr/6>
  iex(3)> x = 2
  2
  iex(4)> f.()
  1