 * unit) =
      (unit * x) = x</code> holds.</p></dd></dl><dl><dt class="spec value" id="val-mconcat"><a href="#val-mconcat" class="anchor"></a><code><span class="keyword">val</span> mconcat : <span><a href="index.html#type-t">t</a> list</span> <span>&#45;&gt;</span> <a href="index.html#type-t">t</a></code></dt><dd><p><code>mconcat xs</code> is the concatenation of all elements in <code>xs</code> into a single value, derived by use of <code>op</code>.</p><p>This is equivalent to <code>List.fold_right op xs