shape trait and Hash

In S02 it is writ, "The key type of a hash may be specified as a shape trait--see S09."

However, S09 is rather brief on hashes, and although it shows using a type inside the curlies, it never talks about shape traits or anything else.

Am I do understand that it pretty much does all the same stuff that Array does?

More globally, nothing is said much about parameters to types.  It shows an example like  Array[of=>T] but never discusses the syntax of defining parameterized types or anything.  Is there a paper or discussion on that I could read?

Thanks,
--John

• shape trait and Hash by John M. Dlugosz
• Re: shape trait and Hash by TSa