over each. See <a href="#val-fold_both"><code>fold_both</code></a> for more usage details. Raises <a href="#exception-Non_blocking_io_expected"><code>Non_blocking_io_expected</code></a> if I/O is blocking.</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-fold_with_proc"><a href="#val-fold_with_proc" class="anchor"></a><code><span><span class="keyword">val</span> fold_with_proc : 
  <span><span class="optlabel">?sleep</span>:float <span class="arrow">&#45;&gt;</span></span>
  <s