Proposal: Add isLeft/isRight to Data.Either

[Edward Kmett]

You can add lens to the list of packages that had to define their own (for
doctest purposes). ;)

On Fri, Nov 30, 2012 at 6:02 PM, Edward Kmett <ekmett at gmail.com> wrote:

> +1
>
> On Fri, Nov 30, 2012 at 3:38 PM, Simon Hengel <sol at typeful.net> wrote:
>
>> Hi,
>> I propose to add isLeft/isRight to Data.Either, with the obvious
>> definitions:
>>
>>     isLeft :: Either a b -> Bool
>>     isLeft (Left  _) = True
>>     isLeft (Right _) = False
>>
>>     isRight :: Either a b -> Bool
>>     isRight (Left  _) = False
>>     isRight (Right _) = True
>>
>> There has been a discussion on that before [1].  While I agree that
>> fromLeft/fromRight are moot, I don't see issues with isLeft/isRight.
>>
>> Personally I care mostly about isLeft, but for orthogonality I propose
>> to add both isLeft and isRight.
>>
>> Here is a (possibly incomplete) list of packages that come with their
>> own definition of isLeft:
>>
>>     snap-core, multifocal, PriorityChansConverger, tamarin-prover-utils,
>>     Agda, PCLT, cmdtheline, scyther-proof, xmlhtml, hspec-expectations,
>>     Glob, language-glsl, Craft3e, hledger-lib, narc, nemesis,
>>     type-settheory, PCLT-DB, RJson, bio, errors, rss2irc, heist
>>
>> Discussion period: 2 Weeks
>>
>> Cheers,
>> Simon
>>
>> [1] http://www.haskell.org/pipermail/libraries/2006-October/006098.html
>>
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>>
>
>
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