Proposal: Add isLeft/isRight to Data.Either

[Andreas Abel]

+1 for Herberts proposal.

On 06.12.12 6:41 AM, Herbert Valerio Riedel wrote:
>
>   - from{Left,Right} are useful when working in the 'Maybe' monad or
>     applicative functor for converting 'Either'-typed values (this also
>     applies to the dual case of working in the 'Either' monad/app-functor
>     and having to deal with 'Maybe' values)
>
>   - IMHO, 'maybeRight' has better readability than inlining 'either
>     (const Nothing) Just' - for me it's not so much about typing less, as
>     more about having code that is easier to read out loud.
>
>   - I often use the 'when'-like combinator 'whenJust' in monadic code:
>
>      whenJust :: Monad m => Maybe a -> (a -> m ()) -> m ()
>      whenJust (Just x) a = a x
>      whenJust _        _ = return ()

+1. whenJust is defined also in Agda.Utils.Monad, should also added to 
Control.Monad.

>   - As the types in Data.Either and Data.Maybe are part of the Haskell
>     standard library, and IMHO basic primitives such as maybe{Left,Right}
>     should be located in those modules as well.

+1

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