Unification and extension of compile-time reflection

[BCS]

Reply to Jarrett,

> The strange is(T U), is(T U : V), is(T U == V) forms.. I'm not sure
> what to do about those.
> 

#2 & 3 are to allow compact type pattern matching. IIRC there not that good 
at it, but are better than nothing.

It's more or less what you bring up in you last point.

Any solution here should include the ability to ask "does type T match pattern 
P if the symbols A B and C (that are part of P) are defined correctly? If 
so, declared A, B and C as needed". You sort of hint at that ability near 
the end, but it needs to be explicit in the design goals.