Author here. Slightly simplifying, a Kleisli arrow is just a function from `A` to `M&lt;B&gt;`, and which is composable, similar to function composition:<p><pre><code>    Kleisli&lt;M, A, B&gt; + Kleisli&lt;M, B, C&gt; = Kleisli&lt;M, A, C&gt;
</code></pre>
Although it is an important part of how the conduits work, it is not strictly necessary for using the library.<p>Would it help if I clarified that somewhere, or would you rather not read &quot;Kleisli&quot; anywhere in the docs?