code class="ml">let validator input =
  let open Validator in
  build build_valid
  |&gt; validate input.age (int_min 13 &quot;Must be 13&quot;)
  |&gt; validate input.email (string_is_email &quot;Must be email&quot;)
  |&gt; keep input.message</code></pre></dd></dl><dl><dt class="spec value" id="val-compose"><a href="#val-compose" class="anchor"></a><code><span class="keyword">val</span> compose : <span><span>(<span class="type-var">'mid</span>, <span class="type-var">'o</span>, <span class="type-var">'e