For example, a compiler must not discard <code>i</code> and reload it
a second time from <code>*p</code> in this program:
</p>

<pre>
i := *p
if i &lt; 0 || i &gt;= len(funcs) {
	panic("invalid function index")
}
... complex code ...
// compiler must NOT reload i = *p here
funcs[i]()
</pre>

<p>
If the complex code needs many registers, a compiler for single-threaded programs

<p>
If <code>a</code> is not a map:
</p>
<ul>
	<li>the index <code>x</code> must be of integer type or an untyped constant</li>
	<li>a constant index must be non-negative and
	    <a href="#Representability">representable</a> by a value of type <code>int</code></li>
	<li>a constant index that is untyped is given type <code>int</code></li>
	<li>the index <code>x</code> is <i>in range</i> if <code>0 &lt;= x &lt; len(a)</code>,

eight bytes at the address specified in <code>R9</code>.
</p>

<p>
If a vector instruction takes a length or an index as an argument then it will be the
first argument.
For example, <code>VLEIF</code> <code>$1,</code> <code>$16,</code> <code>V2</code> will load
the value sixteen into index one of <code>V2</code>.
Care should be taken when using vector instructions to ensure that they are available at
runtime.

<a href="#Length_and_capacity"><code>len</code></a>; unlike with arrays it may change during
execution.  The elements can be addressed by integer <a href="#Index_expressions">indices</a>
0 through <code>len(s)-1</code>.  The slice index of a
given element may be less than the index of the same element in the
underlying array.
</p>
<p>
A slice, once initialized, is always associated with an underlying