k to this headline">¶</a></h2>
<p>The <code class="docutils literal"><span class="pre">fold</span></code> function adaptor uses a binary function to apply a
<a class="reference external" href="https://en.wikipedia.org/wiki/Fold_%28higher-order_function%29">fold</a>
operation to the arguments passed to the function. Additionally, an
optional initial state can be provided, otherwise the first argument is
used as the initial state.</p>
<p>The arguments to the binary function, take first the state and then the