Proposal: Add isLeft/isRight to Data.Either

[Andreas Abel]

On 04.12.12 5:02 PM, Herbert Valerio Riedel wrote:
> Simon Hengel <sol at typeful.net> writes:
>
>> 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.
>
> +1
>
> btw, what I've been missing even more than isLeft/isRight is something
> like
>
> 	leftMaybe :: Either a b -> Maybe a
> 	leftMaybe (Left x) = Just x
> 	leftMaybe _        = Nothing
> 	
> 	rightMaybe :: Either a b -> Maybe b
> 	rightMaybe (Right x) = Just x
> 	rightMaybe _         = Nothing

I have not been missing these, but +1.

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

Theoretical Computer Science, University of Munich
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