d><p>A validator returns a result of:</p><ul><li>Ok output or</li><li>Error (err, err list)</li></ul></dd></dl><dl><dt class="spec type" id="type-validator"><a href="#type-validator" class="anchor"></a><code><span class="keyword">type</span> <span>('input, 'output, 'err) validator</span></code><code> = <span class="type-var">'input</span> <span>&#45;&gt;</span> <span><span>(<span class="type-var">'output</span>, <span class="type-var">'err</span>)</span> <a href="index.html#type-validator_result">validator