If <code>n</code> &lt= 0, the loop does not run any iterations.
</li>

<li>
For a function <code>f</code>, the iteration proceeds by calling <code>f</code>
with a new, synthesized <code>yield</code> function as its argument.
If <code>yield</code> is called before <code>f</code> returns,
the arguments to <code>yield</code> become the iteration values
for executing the loop body once.