a loop that does nothing.</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-fold"><a href="#val-fold" class="anchor"></a><code><span><span class="keyword">val</span> fold : 
  <span><span><span>(<span class="type-var">'stdin</span>, <a href="../Core/index.html#type-stdout">Core.stdout</a>, <span class="type-var">'stderr</span>)</span> <a href="../Core/Cmd/index.html#type-t">Core.Cmd.t</a></span> <span class="arrow">&#45;&gt;</span></span>
  <span><span class="label">f</span>:<sp