r.chr (f (Char.code x)))) b
let d1 = Domain.spawn (update b (fun x -&gt; x + 1))
let d2 = Domain.spawn (update b (fun x -&gt; 2 * x + 1))
let () = Domain.join d1; Domain.join d2
</pre><p>the bytes sequence <code class="code">b</code> may contain a non-deterministic mixture
    of <code class="code">'!'</code>, <code class="code">'A'</code>, <code class="code">'B'</code>, and <code class="code">'C'</code> values.</p>

<p>After executing this code, each byte of the sequence <code class="code">b</code> is eith