"arrow">&#45;&gt;</span></span>
  <span><span>(<span><span class="type-var">'m</span> <span class="arrow">&#45;&gt;</span></span> <span><span class="type-var">'s</span> <span class="arrow">&#45;&gt;</span></span> <span class="type-var">'r</span> * <span class="type-var">'s</span>)</span> <span class="arrow">&#45;&gt;</span></span>
  <span><span class="optlabel">?call</span>:<span>(<span><a href="#type-pf">pf</a> <span class="arrow">&#45;&gt;</span></span> unit)</span> <span class="arrow">&#45;&gt;</span></s