Proposal: add fromRight and fromLeft to Data.Either

Christopher Allen cma at bitemyapp.com
Sat May 21 13:09:28 UTC 2016


I think Edward meant fromJust given the context.

Sent from my iPhone

> On May 21, 2016, at 6:58 AM, David Feuer <david.feuer at gmail.com> wrote:
> 
> No one wants to remove fromMaybe. In fact, it could serve as a template for total fromLeft and fromRight:
> 
> fromLeft :: b -> (a -> b) -> Either a x -> b
> fromRight :: b -> (a -> b) -> Either x a -> b
> 
> On May 21, 2016 8:55 AM, "Edward Kmett" <ekmett at gmail.com> wrote:
> I'm personally -1 on this. 
> 
> A large portion of the community is vehemently against adding new partial functions, and they have to share base with the rest of us. I'd say more people want to remove fromMaybe, head, tail, etc. than want to double down on the pattern at this time.
> 
> -Edward
> 
>> On Fri, May 20, 2016 at 4:08 PM, Anton Felix Lorenzen <anfelor at posteo.de> wrote:
>> When working with Either,
>> I am often missing two simple functions:
>> fromRight :: Either a b -> b
>> fromLeft  :: Either a b -> a
>> 
>> It has been implemented a couple of times:
>> http://hayoo.fh-wedel.de/?query=fromRight
>> 
>> But I don't want to depend on yet another library
>> for such a basic function.
>> 
>> Could it be added?
>> 
>> Anton
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> 
> 
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