options. <code>None</code> is used to for actuals that cannot be resolved to an address (eg local-rooted paths or arithmetic expressions).</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-pp_subst"><a href="#val-pp_subst" class="anchor"></a><code><span><span class="keyword">val</span> pp_subst : <span><span class="xref-unresolved">F</span>.formatter <span class="arrow">&#45;&gt;</span></span> <span><a href="#type-subst">subst</a> <span class="arrow">&#45;&gt;</span></span> unit