?&#8288;verbose_period:int <span class="keyword">&#8209;&gt;</span> ?&#8288;tos:(<span class="type-var">'a</span> <span class="keyword">&#8209;&gt;</span> string) <span class="keyword">&#8209;&gt;</span> len:int <span class="keyword">&#8209;&gt;</span> (<span class="type-var">'a</span> <span class="keyword">&#8209;&gt;</span> unit Lwt.t) <span class="keyword">&#8209;&gt;</span> unit Lwt.t</code></div><div class="doc"><p>Note that <code class="code">tester</code> does not comply with non-lwt exceptions: some