> <span class="arrow">&#45;&gt;</span></span>
  <span><span class="type-var">'b</span> <span class="arrow">&#45;&gt;</span></span>
  <span><a href="#type-t">t</a> <span class="arrow">&#45;&gt;</span></span>
  <span class="type-var">'b</span></span></code></div><div class="spec-doc"><p>Same function as <code>fold</code> but filters segments with the first argument</p></div></div><div class="odoc-spec"><div class="spec value" id="val-perimeter" class="anchored"><a href="#val-perimeter" class="anchor"></a><cod