Proposal: merge Data.Functor.Coproduct into transformers

wren ng thornton wren at
Tue Dec 11 13:42:03 CET 2012

On 12/11/12 7:27 AM, Mario Blazevic wrote:
> On Tue, Dec 11, 2012 at 5:29 AM, Edward Kmett <ekmett at> 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?


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.

> Nah, those constructor names are dumb. I prefer Shaun's
>> data Sum f g a = SumLeft (f a) | SumRight (g a)

-1. What happened to the vaunted brevity? I type out the names of data 
constructors far more often than the names of type constructors. And 
those data constructor names are obnoxiously long for something as basic 
as a functor coproduct.

Live well,

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