viously you'll probably eventually run into a situation where you need to subtract everything in a <code>list</code> or <code>array</code> starting from some initial value, which is where magmas shine. Monoids will be exlpained more in the next section.</p><h4 id="monoidal-categories"><a href="#monoidal-categories" class="anchor"></a>Monoidal Categories</h4><p><i>- &quot;A monad is just a monoid in the category of endofunctors, what's the problem?&quot;</i></p><p>This quote is often cited in the FP communit