 parameter does. For instance, if some variable <code>X</code> has a huge number of fields, the only terminal field of <code>X#field1</code> will be <code>X</code> itself.</p><p>If the summary is <code>None</code>, <code>f</code> will be called once with a var-only abstract cell.</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-fold_argument"><a href="#val-fold_argument" class="anchor"></a><code><span><span class="keyword">val</span> fold_argument : 
  <span><span><a href="#typ