sion creates an anonymous function that adds twice the first
argument to the second, and then calls that function with arguments 10 and 20.
This will return (10 + 10 + 20) = 40.
</p>
<p>There is a common macro <code class="mendoza-code">defn</code> that can be used for creating functions and
immediately binding them to a name. <code class="mendoza-code">defn</code> works as expected at both the
top level and inside another form. There is also the corresponding macro
<code class="mendoza-code">defmacro</code