span class="arrow">&#45;&gt;</span></span> <span><a href="#type-expr">expr</a> <span class="arrow">&#45;&gt;</span></span> <a href="#type-expr">expr</a></span></code></div><div class="spec-doc"><p><code>ppr_expr env e</code> should return the result of pre-processing expression <code>e</code> in env <code>env</code>. The optional argument <code>expected_type</code> can be used to perform type-dependent transformations. A typical usage is to rewrite <code>0</code> (resp <code>1</code>) as <code>false</code> 