ty = [1; 2; 3];;
val satisfies_identity_law : bool = true

# let satisfies_associative_law =
  List.append [1] (List.append [2; 3] [4]) = List.append (List.append [1] [2; 3]) [4];;
val satisfies_associative_law : bool = true</code></pre></li><li><p>The <a href="Bastet/Option/Plus/index.html"><code>Bastet.Option.Plus</code></a></p><pre><code class="ml"># let empty: [ `foo ] option = None;;
val empty : [ `foo ] option = None

# let append a b =
  match a, b with
  | Some x, _ -&gt; Some x
  | None, y -&gt; y;