Add Functor/Applicative instances for all Monads in GHC

Simon Peyton-Jones simonpj at
Wed May 8 16:19:56 CEST 2013


As I understand this, it's a library issue, nothing to do with GHC per se.  As such you need to follow the library-submission process

Once the libraries folk are satisfied, we're quite happy to incorporate the library changes in the next revision of GHC.

We are seeing increasing resistance to un-forced library API changes, along the lines of "don't gratuitously break my code!".  The libraries list is the right place to have that debate.


| -----Original Message-----
| From: ghc-devs-bounces at [mailto:ghc-devs-bounces at]
| On Behalf Of David Luposchainsky
| Sent: 08 May 2013 12:50
| To: ghc-devs at
| Subject: Add Functor/Applicative instances for all Monads in GHC
| Hello GHC devs,
| due to the formation of the Haskell Prime Committee [1], I am motivated
| to propose another go at the "Applicative => Monad" issue. Regardless of
| the future of that proposal, I think some changes required by it are
| beneficial in any case, namely ensuring that all Monads defined in GHC
| get Applicative/Functor instances.
| I've successfully modified toy version of 7.6.3 to include these
| instances to see how it goes, and as you can imagine the changes are
| numerous but simple; I don't assume HEAD won't be much different in that
| respect.
| However, since this would by my first involvement in a project as large
| as GHC, I am not quite sure of the procedure to follow, even after
| reading the corresponding Trac/Wiki pages. I'm assuming the policy here
| is the same as for the libraries mailing list (hence this email), and
| upon positive feedback I can open a Trac issue, take ownership, clone,
| modify, send pull request etc. If there's anything wrong with that
| approach here please tell me.
| Greetings,
| David
| [1]
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