need some clarification on compile-time type vs. run-time type

[P T Withington]

On 2007-11-12, at 02:04 EST, Brendan Eich wrote:

>                                                 Imagine explicit
> parenthese (not allowed because they mean union type, but pretend)

I was just thinking how clever it was that parentheses meant both  
union type and expression grouping, because a union type of only one  
type is that type, so you could use parentheses here?

>   x is (like T)

What am I missing?