I'd like to start the discussion about feature request #166, "List instances for a type in GHCi".  In short, the idea is that we add a new command to GHCi, `:instances TYPE`, which given a type, will show the list of instances---for any class---that could be used with this type.

It seems like this could be a potentially handy thing to do, and it doesn't really interfere with anything else, so I recommend that we accept it.

Please let me know what you think.

-Iavor