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

Twan van Laarhoven twanvl at gmail.com
Tue Feb 24 16:14:45 UTC 2015


(+1) to both.

On 2015-02-24 16:39, 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
>
>
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