rocedural approach, without
introducing any forward references:</p>

<blockquote><pre>
<span class="keyword">def</span> <span class="function-name">string_append</span>(s1, s2):
    buf = make_string(<span class="py-builtins">len</span>(s1) + <span class="py-builtins">len</span>(s2))
    idx = 0
    <span class="keyword">while</span> idx != <span class="py-builtins">len</span>(s1):
        buf[idx] = s1[idx]
        idx += 1
    length = <span class="py-builtins">len</span>(s1)
    <span class="keyword">whi