darcs patch: Adding isLeft, isRight, fromLeft, fromRight, splitEithers

Bulat Ziganshin bulat.ziganshin at gmail.com
Tue Oct 31 06:20:04 EST 2006

Hello Ross,

Tuesday, October 31, 2006, 11:59:56 AM, you wrote:

> splitEithers (the Either counterpart of catMaybes) is a great idea.
> (Except maybe for the name; all these split's are getting confusing.)
> See also mapEither (the counterpart of mapMaybe) in Data.Map.

> I'm not so keen on isLeft, isRight, fromLeft and fromRight.  Pattern
> matching is clearer and safer: at the point you make the decision, the
> type system has the extra information about the branch you've chosen.
> It also pushes the programmer to put the decision and the use of the data
> together, another good thing.  The isJust/fromJust combination is already
> a rich source of bugs; we don't need more.  (Same goes for null/head/tail,
> of course.)

nevertheless, we want to use them all :)   "don't teach me a life,
just give some money :)"

Best regards,
 Bulat                            mailto:Bulat.Ziganshin at gmail.com

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