Re: Proposal: Add isLeft/isRight to Data.Either

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 wrote:

+1

On Fri, Nov 30, 2012 at 3:38 PM, Simon Hengel 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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