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

On 11.12.12 1:48 PM, Gábor Lehel wrote:

On Tue, Dec 11, 2012 at 1:42 PM, wren ng thornton wrote:

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On 12/11/12 7:27 AM, Mario Blazevic wrote:

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

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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?

+1.

I hesitate to suggest another alternative, but if folks are displeased with those names, there's always the tried and true InL/InR or InjL/InjR. But given the precedent of Either, I think LeftF/RightF have a nice ring to them.

Another possibility is

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

But +1 to the proposal no matter the names, +1 to LeftF/RightF, +0 to any particular type name (including this one).

That sounds better to me than Coproduct or Sum which smell too much of theory. An alternative would be data Either1 f g a = Left1 (f a) | Right1 (g a) to indicate the arity of the functor. (The current Either is Either0.) One can go on this way and have bifunctors data Either2 f g a b = Left2 (f a b) | Right2 (g a b) and so on... -- 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/