ncat" class="anchor"></a><code>| </code><code><span class="constructor">Concat</span></code></td></tr></table></dt><dt class="spec type" id="type-exp"><a href="#type-exp" class="anchor"></a><code><span class="keyword">type</span> <span>('a, 'v, 'b, 'm) exp</span></code><code> = </code><table class="variant"><tr id="type-exp.Var" class="anchored"><td class="def constructor"><a href="#type-exp.Var" class="anchor"></a><code>| </code><code><span class="constructor">Var</span> <span class="keyword">of</span> <sp