Proposal: merge Data.Functor.Coproduct into transformers

Gábor Lehel illissius at
Tue Dec 11 13:48:44 CET 2012

On Tue, Dec 11, 2012 at 1:42 PM, wren ng thornton <wren at> wrote:
> 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?
> +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).

Your ship was destroyed in a monadic eruption.

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