Maybe.concat and Maybe.concatMap

[FRosner]

Problem

Elm does not have a generic implementation of higher order collection functions like map, filter, flatten/concat, etc. While this is not a problem per se it is useful to have the individual APIs available in a consistent way. This way you can generalize the API in your head when using it.

While, e.g., List.concat and List.concatMap exists, there is no Maybe.concat and Maybe.concatMap available.

Solution

Implement Maybe.concat and Maybe.concatMap in order to have a consistent API of both functions between List and Maybe.

Note

I read that you are strict about extending the core API and new functions should be proposed to *-extra first. While this makes sense for contributions that introduce additional concepts, this contribution adds already existing functionality to a place where it is missing. I think that having a consistent collection API is a strong feature and useful to have in the core API.

Anyway, ❤️ Elm.

[process-bot]

Thanks for the pull request! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[process-bot]

Thanks for the pull request! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[lukewestby]

Some quick thoughts I have:
concatMap and andThen are the same function, and concat can be derived from it as andThen identity. So the value here would be mostly in the names of the functions for consistency across List and Maybe rather than in previously unavailable functionality.

In any case, @FRosner, these kind of changes need to be discussed on the mailing list before any code gets accepted. Can you bring this up on elm-dev and get some feedback from other folks?

[lukewestby]

Some quick thoughts I have:
concatMap and andThen are the same function, and concat can be derived from it as andThen identity. So the value here would be mostly in the names of the functions for consistency across List and Maybe rather than in previously unavailable functionality.

In any case, @FRosner, these kind of changes need to be discussed on the mailing list before any code gets accepted. Can you bring this up on elm-dev and get some feedback from other folks?

[FRosner]

You are totally right @lukewestby ¬_¬

So I guess I'll have to bring this up to the mailing list in terms of the consistency discussions (flatMap being called concatMap in List and andThen in Maybe).

Thanks for the comment.

[FRosner]

You are totally right @lukewestby ¬_¬

So I guess I'll have to bring this up to the mailing list in terms of the consistency discussions (flatMap being called concatMap in List and andThen in Maybe).

Thanks for the comment.

[richardhaven]

Emerson

As these methods do different things, rather than the same things on different objects, it is almost confusing that they have the same names.

[richardhaven]

Emerson

As these methods do different things, rather than the same things on different objects, it is almost confusing that they have the same names.