specifying the key Type for a Hash

[Abhijit Mahabal]

A6 included examples of syntax for specifying the type of the key for a 
hash:

my %pet is Hash(keytype => Str, returns => Cat)
None of the synopses have anything like this. S6 talks about the 
types of values, but not keys. Oversight, or is this syntax dead?

--abhijit
Abhijit Mahabal      http://www.cs.indiana.edu/~amahabal/