func()(x)        // function signature func() x
(func())(x)      // x is converted to func()
(func() int)(x)  // x is converted to func() int
func() int(x)    // x is converted to func() int (unambiguous)
</pre>

<p>
A <a href="#Constants">constant</a> value <code>x</code> can be converted to
type <code>T</code> if <code>x</code> is <a href="#Representability">representable</a>
by a value of <code>T</code>.