valid
  |&gt; validate input.hobbies (list_every hobbie_validator)</code></pre></dd></dl><dl><dt class="spec value" id="val-option_is_some"><a href="#val-option_is_some" class="anchor"></a><code><span class="keyword">val</span> option_is_some : <span><span>(<span><span class="type-var">'a</span> option</span>, <span class="type-var">'a</span>, <span class="type-var">'err</span>)</span> <a href="index.html#type-validator_builder">validator_builder</a></span></code></dt><dd><p>Validate that a value is not N