How to specify versions of ports?

[Max Brown]

> Do you have it still installed, but not activated?
> sudo port installed ghc

$ sudo port installed ghc
Port ghc is not installed.
No ports are installed.

(No ports are installed??? Actually, when I run "port installed", I
get a list of some stuff, ghc is just not on that list. Phew.)

How did I manage to break this? Are the files in my package directory
worthless now?