e-var">'err</span>)</span> <a href="index.html#type-validator_builder">validator_builder</a></span></code></dt><dd><p>Validate that a list is not empty</p><pre><code class="ml">let validator input =
  let open Validator in
  build build_valid
  |&gt; validate input.hobbies (list_is_not_empty &quot;Must have a hobby&quot;)</code></pre></dd></dl><dl><dt class="spec value" id="val-list_has_max_length"><a href="#val-list_has_max_length" class="anchor"></a><code><span class="keyword">val</span> list_has_max_leng