Re: Proposal: Add (<$>) to Prelude as part of the AMP in GHC 7.10-RC3

This is a tough call for me. This change will be very annoying, I think. When updating for 7.10, I was quite surprised that I still needed to import Control.Applicative for <$>, and put in the CPP to do so. Now I'll have to remove that from quite a few modules. Given that we plan only a week for RC3, there are a lot of modules in the ecosystem that will have to be updated within that week! Of course, an author who doesn't update (by removing the now-redundant import of <$>) just gets a warning, but it's still annoying. In my opinion, little changes like this, made right before the deadline, make Haskell feel more like a little research language than something meant to support industrial work. All that said, I desperately miss having <$> in the Prelude in 7.10. Hence the tough call. 0 from me, then. Richard On Feb 24, 2015, at 10:47 AM, Christopher Reichert wrote:

+1 on <$>. Indifferent on <$.

-Christopher

On Tue, Feb 24 2015, Edward Kmett wrote:

...

We have a couple of weeks until the third release candidate for GHC 7.10 goes out the door.

Along the way with the last couple of release candidates folks have found some problems with the way we implemented the AMP. [1][2]

Most notably, we failed to include (<$>) in the Prelude, so the standard idiom of

foo <$> bar <*> baz <*> quux

doesn't work out of the box!

I'd like to include (<$>) in the Prelude in RC3.

I'd also like to invite discussion about whether folks believe we should include (<$) out of the box.

(<$) has been a member of Functor for a long time, which is only visible if you import it from Data.Functor or bring in Control.Applicative. There is an idiom that you use (<*) and (<$) to point to the parts of the structure that you want to keep the answers from when building longer such Applicative chains.

Discussion Period: 2 weeks

Thank you, -Edward Kmett

[1] http://www.reddit.com/r/haskell/comments/2wzixa/shouldnt_be_in_prelude/ [2] https://plus.google.com/115504368969270249241/posts/URzeDWd7qMp _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

-- Christopher Reichert irc: creichert gpg: C81D 18C8 862A 3618 1376 FFA5 6BFC A992 9955 929B _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries