element type, indexed by a set of unique <i>keys</i> of another type,
called the key type.
The value of an uninitialized map is <code>nil</code>.
</p>

<pre class="ebnf">
MapType     = "map" "[" KeyType "]" ElementType .
KeyType     = Type .
</pre>

<p>
The <a href="#Comparison_operators">comparison operators</a>
<code>==</code> and <code>!=</code> must be fully defined