><span>{</span></code><ol><li id="type-simple_expression.head" class="def record field anchored"><a href="#type-simple_expression.head" class="anchor"></a><code><span>head : <a href="#type-expression">expression</a>;</span></code></li><li id="type-simple_expression.tail" class="def record field anchored"><a href="#type-simple_expression.tail" class="anchor"></a><code><span>tail : <a href="#type-expression">expression</a>;</span></code></li></ol><code><span>}</span></code></li><li id="type-simple_expression.