 the types need to satisfy. This succinct and hopeful more useful introduction is ideally all you will need to understand the core concepts and be productive.</p><p>You can try all of the examples here with <a href="https://opam.ocaml.org/packages/utop">utop</a>.</p><h4 id="functors"><a href="#functors" class="anchor"></a>Functors</h4><p>Functors generalize the notion of something that's <i>composably mappable</i>. You're probably already familiar with this concept from javascript's <a href="https://develop