Changes to Typeable

[Dominique Devriese]

Small note while I happen to be reading the list:

2012/10/3 Simon Peyton-Jones <simonpj at microsoft.com>:
>    Plan A (easy): make GHC derive Typeable for everything, deprecate
>             all uses of 'deriving Typeable'.  Small downside: some programs
>             that are currently rejected will be accepted.

Does this imply forbidding user-written instances of Typeable? If yes,
then I guess some currently accepted programs would also be rejected
(those with manual instances)?  If not, then wouldn't there be
duplicate instances? Or would manual instances somehow take priority?
Or be ignored?

Dominique