So basically the idea here is that you want to have TS-style untagged unions, but instead they're also tagged, but still unify and compose the way they do in TS

So basically the idea here is that you want to have TS-style untagged unions, but instead they're also tagged, but still unify and compose the way they do in TS? Then why couldn't you just do `{ tag: A, data: … } | { tag: B, … } | { tag: C, … }`? Wouldn't it solve your problem? We didn't start with composability as a requirement but you're right in that if it's a goal then nesting Either's is a rather poor solution. A better fit would be variants based on row polymorphism as I described in the reply to the other poster. It wouldn't be a 1:1 mapping to your first example though, if your union is ultimately closed (as in your first example) then you'd still need to have one extra no-op function call to unify the types. Not a big deal but row-polymorphic variants lose here. On the other hand, IMO the possibility of having them open as well is the killer feature. Ultimately though, I don't like this style of type unification as the one happening in your first example. Shaped by the languages I'm working with, I simply don't end up in situations where I'd need something like this. I just approach the problems differently. But this is more of a subjective territory here.