>define</span> (delay-it exp env) (<span class="fu">list</span> <span class="qu">'thunk</span> exp env))
(<span class="kw">define</span> (thunk? obj) (tagged-list? obj <span class="qu">'thunk</span>))
(<span class="kw">define</span> (thunk-exp thunk) (<span class="fu">cadr</span> thunk))
(<span class="kw">define</span> (thunk-env thunk) (<span class="fu">caddr</span> thunk))</code></pre>
<ul>
<li>To memoize thunks, <code>force-it</code> becomes a bit more complicated.</li>
</ul>
<aside><h4>Exercises:</h4> <