Add Applicative instances for MTL types

[Bas van Dijk]

Hello,

In a project of mine I needed an Applicative instance for Identity and
noticed it didn't exist. So I decided to add Applicative (and
Alternative instances where possible) for all MTL types.

When I was about to submit a library proposal I saw there already
existed one. So I added my patch to that ticket.

My patch I different in that my Applicative instances don't require a
Monad constraint. This also means that most Functor instances now also
depend on Applicative rather than on Monad.

See the ticket for the details:

http://hackage.haskell.org/trac/ghc/ticket/2316

Discussion period: 5 weeks (taking the holidays into account)

This is the old thread about this proposal:

http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9140/focus=9154

regards,

Bas