So far we have a consensus on the proposal (yay!), but no firm agreement on the naming. Of the two alternatives I've suggested, Sum appears to have edged ahead of Coproduct. Let me know if I misrepresented anybody's position: Edward Coproduct (LeftF | RightF) Erik Sum Wren Coproduct (InL | InR) Gábor ? (LeftF | RightF) Andreas Either1 (Left1 | Right1) Sean Sum (InL | InR) Henning Sum no prefixes Unfortunately, there seems to be a preference for a new data type instead of a newtype wrapping for Either, which gives us three bike sheds to paint instead of one. I'm going to list some of the suggested alternatives here:
data Coproduct f g a = LeftF (f a) | RightF (g a) data Sum f g a = InL (f a) | InR (g a) data Either1 f g a = Left1 (f a) | Right1 (g a) data Either f g a = Left (f a) | Right (g a) -- use qualification
I like the Either1 naming, but only if it's a start of a new trend. In other words, that's a good choice only if it gains a consensus so that other higher-order types switch to the scheme in the future. If that doesn't happen, my second choice would be Sum (InL, InR).