[plt-scheme] Typed Scheme: vector-length isn't bound in the typed-scheme language

> Subject says it all.

I'm still learning Typed Scheme, so hopefully someone can correct me if 
I'm going astray.  I see a set of environmental definitions in the 
private/base-env.ss file using Typed Scheme 1.5.

I added the following to the definition of the "initial-env" near the 
bottom:

        [vector-length (-poly (a) (-> (make-vec a) N))]

It probably doesn't matter where it goes as long as it's with the other 
type declarations, but I put this right next to the definitions of the 
types for vector->list and list->vector.  Afterwards, vector-length 
appeared to typecheck ok for me.


But "string-length" and "string-ref" also appears to be missing.  Would 
the following be correct types for those?

        [string-length (-String . -> . N)]
        [string-ref (-String N . -> . -Char)]


Best of wishes!