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

On 04.12.12 5:02 PM, Herbert Valerio Riedel wrote:

Simon Hengel 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 Oettingenstr. 67, D-80538 Munich, GERMANY andreas.abel@ifi.lmu.de http://www2.tcs.ifi.lmu.de/~abel/