rfc: include bimap into Data.Either

[Andreas Abel]

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+1 to all three amendments.

On 20.04.2014 19:20, Dominique Devriese wrote:
> First, here is a link to a post by Andreas in a previous discussion
> on this list about the same topic 
> http://www.haskell.org/pipermail/libraries/2013-August/020549.html
> 
> Speaking only for myself, I would happily support a generalisation 
> like "mapEither is just a special case of Bifunctor.fmapBoth". 
> However, I'm unsatisfied with "mapEither is just a special case of 
> Control.Arrow.(+++)". The reason is that when I need, e.g., the 
> mapEither function, I'm looking for a function of type "(a -> b) ->
> (c -> d) -> Either a c -> Either b d".  To find such a function, I
> focus on the Eithers in this signature and start looking for a
> function related to the Either data type, or some generalisation of
> it.  I would naturally expect to find such a function in
> Data.Either or Data.Bifunctor or similar places. However, in order
> to find Control.Arrow.(+++), I would instead have to focus on the
> (->)s in the signature and look for a function that works on a
> generalisation of the (->)s, i.e. Arrow.  For me, and I expect also
> for beginners and people unacquainted with arrows, I think this is
> *not* an obvious generalisation.
> 
> As for a concrete counter-proposal, I would propose to amend
> Tobias' original proposal with three bikeshedding modifications
> (partially overlapping with other people's suggestion in this
> thread and the one from 2013): * rename bimap to mapEither (or
> perhaps mapBoth) * implement the functions as renames when
> possible: "mapEither = Control.Arrow.(+++)" and similarly. * also
> add "mapRight :: (a -> b) -> Either c a -> Either c b"
> 
> Regards, Dominique
> 
> 2014-04-20 17:52 GMT+02:00 Herbert Valerio Riedel <hvr at gnu.org>:
>> On 2014-04-20 at 17:29:39 +0200, Dominique Devriese wrote:
>>> 2014-04-20 14:29 GMT+02:00 Andreas Abel
>>> <andreas.abel at ifi.lmu.de>:
>>>> On 20.04.2014 07:16, João Cristóvão wrote:
>>>>>> given arrowchoice, i withdraw my proposal. thank you for
>>>>>> pointing me
>>>>> there.
>>>>> 
>>>>> Please don't.
>>>> 
>>>> +1
>>>> 
>>>> Stuff like this belongs in Data.Either, not in Control.Arrow.
>>>> We had the same issue for Data.Tuple vs. Control.Arrow a
>>>> while ago.
>>> 
>>> +1
>> 
>> I'm slightly confused, what are you exactly voting for? For
>> augmenting the documentation in Data.Either to mentioning e.g.
>> Control.Arrows (or even Bifunctor), or rather for adding new
>> functions to Data.Either?
> 


- -- 
Andreas Abel  <><      Du bist der geliebte Mensch.

Department of Computer Science and Engineering
Chalmers and Gothenburg University, Sweden

andreas.abel at gu.se
http://www2.tcs.ifi.lmu.de/~abel/
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