Re: Proposal: merge Data.Functor.Coproduct into transformers

On Tue, 11 Dec 2012, Mario Blazevic wrote:

On Tue, Dec 11, 2012 at 5:29 AM, Edward Kmett wrote:

...

I'm not wedded to its current behavior of wrapping an Either. It was kind of nice that converting to and from Either was a no-op on GHC, but that could change.

I agree that I wouldn't want to add functions named 'left' and 'right', so moving to a data type rather than a newtype seems reasonable.

Perhaps

data Coproduct f g a = LeftF (f a) | RightF (g a)

would be a nice color for the bikeshed?

Nah, those constructor names are dumb. I prefer Shaun's

...

data Sum f g a = SumLeft (f a) | SumRight (g a)

If we're going with Sum, of course.

Please stop emulating qualification with custom prefixes or suffixes. We have real qualification! (On the other hand you can throw in that 'transformers' is already designed for unqualified import.) I find the analogies to algebraic sums and products appealing, thus I would prefer Sum to Coproduct. But I would also be very happy with Either(Left, Right) plus qualification.