Support all top-level declarations in GHCi
I thought we had a ticket for this, but I can't find it so I'm creating one.
In GHCi there's no reason in principle that we can't allow any declaration that you can write at the top-level of a source file, at the interactive prompt. Many people have asked for this over the years.
- data/type/newtype declarations
- class declarations
- instance declarations
- foreign declarations (exception foreign export)