Gus

@Lanayx you are right, I used your code (with the extension) to test it, but now I tested with the latest 10 preview and it runs as expected. I still...

There's already an implementation for both `Map.union` and `Map.unionWith` [here in F#+](https://github.com/fsprojects/FSharpPlus/blob/6170f01537224c69d2f8fd5146a91b7978b6381f/src/FSharpPlus/Extensions.fs#L373-L378). Also for Dictionaries and ReadOnlyDictionaries. I prefer to leave the name `merge` for the applicative operation.

I think `choose` is not exactly a `filter` or a `Where`. It's a kind of flatten for a Collection of options (or something that maps to option). Having said that,...

A possible specification would be a function equivalent to: `let concat x = x |>> map result |>> sum |> join` which could be further simplified to `let concat x...

@Happypig375 I don't think that #8443 render this unneeded. I think this is a good suggestion and it's very helpful to quickly test regressions. @cartermp > It's complicated mostly because...

Would it be the same way as it is in C#?