Re: The future of the haskell2010/haskell98 packages - AKA Trac #9590

Hi Malcolm, Withdrawing the packages from GHC's distribution is certainly a possibility. We did briefly raise that point when we talked yesterday too, but it wasn't discussed much. Perhaps some others feel the same, but I imagine more people would be OK with #2 above as opposed to eliminating it, since we already lightly break some things anyway. Hopefully we'll really find out soon. On Tue, Sep 30, 2014 at 4:00 PM, Malcolm Wallace wrote:

How about doing the honest thing, and withdrawing both packages in ghc-7.10? Haskell'98 is now 15 years old, and the 2010 standard was never really popular anyway.

Regards, Malcolm

On 30 Sep 2014, at 21:21, Austin Seipp wrote:

Hello developers, users, friends,

I'd like you all to weigh in on something - a GHC bug report, that has happened as a result of making Applicative a superclass of Monad:

https://ghc.haskell.org/trac/ghc/ticket/9590

The very condensed version is this: because haskell2010/haskell98 packages try to be fairly strictly conforming, they do not have modules like Control.Applicative.

Unfortunately, due to the way these packages are structured, many things are simply re-exported from base, like `Monad`. But `Applicative` is not, and cannot be imported if you use -XHaskell2010 and the haskell2010 package.

The net result here is that haskell98/haskell2010 are hopelessly broken in the current state: it's impossible to define an instance of `Monad`, because you cannot define an instance of `Applicative`, because you can't import it in the first place!

This leaves us in quite a pickle.

So I ask: Friends, what do you think we should do? I am particularly interested in users/developers of current Haskell2010 packages - not just code that may *be* standard Haskell - code that implies a dependency on it.

There was a short discussion between me and Simon Marlow about this in the morning, and again on IRC this morning between me, Duncan, Edward K, and Herbert.

Basically, I only see one of two options:

- We could make GHC support both: a version of `Monad` without `Applicative`, and one with it. This creates some complication in the desugarer, where GHC takes care of `do` syntax (and thus needs to be aware of `Monad`'s definition and location). But it is, perhaps, quite doable.

- We change both packages to export `Applicative` and follow the API changes in `base` accordingly.

Note that #1 above is contingent on three things:

1) There is interest in this actually happening, and these separate APIs being supported. If there is not significant interest in maintaining this, it's unclear if we should go for it.

2) It's not overly monstrously complex (I don't think it necessarily will be, but it might be.)

3) You can't like `haskell2010` packages and `base` packages together in the general case, but, AFAIK, this wasn't the case before either.

I'd really appreciate your thoughts. This must be sorted out for 7.10 somehow; the current situation is hopelessly busted.

-- Regards,

Austin Seipp, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/ _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://www.haskell.org/mailman/listinfo/ghc-devs

-- Regards, Austin Seipp, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/