type is <code>nil</code>.
</p>

<pre class="ebnf">
FunctionType  = "func" Signature .
Signature     = Parameters [ Result ] .
Result        = Parameters | Type .
Parameters    = "(" [ ParameterList [ "," ] ] ")" .
ParameterList = ParameterDecl { "," ParameterDecl } .
ParameterDecl = [ IdentifierList ] [ "..." ] Type .
</pre>

<p>
Within a list of parameters or results, the names (IdentifierList)