href="#type-env">env</a> <span class="arrow">&#45;&gt;</span></span> <span><a href="Syntax/index.html#type-expr">Syntax.expr</a> <span class="arrow">&#45;&gt;</span></span> bool</span></code></div><div class="spec-doc"><p><code>eval_bool env e</code> should return the boolean value obtained by evaluating expression <code>e</code> in environment <code>env</code>. Should raise <a href="#exception-Illegal_expr"><code>Illegal_expr</code></a> if <code>e</code> does not denote a boolean value or in case of failur