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

[Adam Bergmark]

+1 for <$>, 0 on <$, I rarely use it.



On Tue, Feb 24, 2015 at 7:25 PM, Conor McBride <conor at strictlypositive.org>
wrote:

>
> On 24 Feb 2015, at 15:39, Edward Kmett <ekmett at gmail.com> 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.
>
> For more on this idiom (indeed), let me shamelessly plug
>
>   http://stackoverflow.com/a/15124278/828361
>
> and advise that the two travel together.
>
> I won’t vote. While we are still in the situation that progress breaks
> code which has been
> engineered to work around the prior lack of progress, making progress is
> simultaneously
> a good and bad idea. We should think about how to adapt our language of
> imports to
> accept the only too obvious reality that libraries change over time, so
> that we might be
> allowed to program defensively against sudden outbreaks of common sense.
>
> Apologetically
>
> Conor
>
> >
> > 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
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