Update for 0.19

[mattjbray]

Thanks @stoeffel for the initial work on this.

Needs some changes in elm-export for 0.19.

[FranklinChen]

Any more on this?

[FranklinChen]

Should I pick up where this was left off since it hasn't been finished yet?

[mattjbray]

@FranklinChen I think this is all that is needed in servant-elm - in theory this PR is ready to go. But it looks like elm-export needs some changes for 0.19 - e.g. decode has been removed from elm-json-decode-pipeline. There might be others.

[domenkozar]

@mattjbray maybe we should revisit the decision of keeping elm-export and move to elm-bridge, which seems superior in terms of features and it's already Elm 0.19 ready. I think supporting two backends wouldn't yield many benefits and would have maintenance overhead.

My 2c, thanks for this PR. There is some work on Elm 0.19 in this branch: https://github.com/matsubara0507/elm-export/commits/elm-0.19

[domenkozar]

@mattjbray this PR breaks my codebase because it doesn't support newtypes anymore for encoding parts of the url. Could newtypes around strings be easily supported or maybe allow to manually define toString for them.

[domenkozar]

Something like http://blog.stermon.com/articles/2018/04/09/elm-stringeable-types-library-for-elm-019.html would allow compile-time check and one would have to implement those manually.

On second thought, having those inpuits as String would also work for now.

[domenkozar]

Would also cover https://github.com/mattjbray/servant-elm/issues/35

[FranklinChen]

What's the current status of elm-export use?

[domenkozar]

elm-export PR: https://github.com/krisajenkins/elm-export/pull/54

[saurabhnanda]

Apologies for butting into this PR.

I'm working on API code-gen for Elm 0.19 based off elm-bridge and am looking at servant-elm for inspiration. If I look at the Elm docs for Http it seems that it is no longer possible to return an Http.Response a from any function in that module. You are forced to return a Cmd Msg. Have I understood this correctly?

I tried loading the one of the generated sample Elm file from this branch - https://github.com/mattjbray/servant-elm/blob/f665ddd5cefac26b3e56981f3516772d3987a6f3/examples/books/elm/Generated/BooksApi.elm - and got a bunch of these errors:

> import BooksApi
-- NAMING ERROR ----------------------------------------------- src/BooksApi.elm

I cannot find a `Http.Request` type:

70| getBooksByBookId : Int -> Http.Request (Book)
                              ^^^^^^^^^^^^
The `Http` module does not expose a `Request` type. These names seem close
though:

    Http.Expect
    Http.Header
    Http.Progress
    Http.Response

Hint: Read <https://elm-lang.org/0.19.0/imports> to see how `import`
declarations work in Elm.

Does this mean that ElmOptions will have to evolve to include an "API-endpoint <> Elm-message mapping"? Another solution could be to have a Servant-level type-combinator, say ElmMessage to achieve the same, eg.:

type Api = "books" :> Capture "bookId" Int :> ElmMessage "BookReceived" :> Get '[JSON] Book

If I have understood this correctly, isn't this a big spanner thrown by Elm 0.19 wrt API code-generation?

[saurabhnanda]

Another solution could be to generate functions that take a Msg as one of the arguments, eg:

type Msg = BookReceived (Result Http.Error Book)

getBookById : Msg -> Int -> Cmd Msg
getBookById msg bookId = Http.get
  { url = "/books/" ++ (String.fromInt bookId)
  , expect = Http.expectJson msg Book.decode
  }

This might not be a bad idea after all. One might want to emit different messages for different call-sites of getBooksById. This brings down the "alarm level" from my side for sure 😄

[domenkozar]

I have hit the same issue and it's possible to use generics, but as soon as there is a manual instance in Haskell, something like http://blog.stermon.com/articles/2018/04/09/elm-stringeable-types-library-for-elm-019.html would work.

[saurabhnanda]

@domenkozar didn't understand your comment completely. Does https://github.com/mattjbray/servant-elm/pull/45#issuecomment-446224280 not solve the problem? I've taken a stab at a POC at https://github.com/agrafix/elm-bridge/issues/40#issuecomment-446240811

[domenkozar]

@saurabhnanda sorry, wrong thread :)

[AesaKamar]

Were there any additional conclusions that've come out of this regarding next steps to be taken to support Elm 0.19?

[szg251]

I forked this repo and made it compatible with 0.19 but it needs elm-export to be updated too. I think this PR should be alright, but seems to be abandoned.

Here's my repo: https://github.com/gege251/servant-elm Since the elm-export package is referenced by a git url I'm not sure if I should create a new PR.

[k-bx]

Reposting here since this place is more relevant than an elm-export PR:

I've made another fork. I've replaced elm-export with elm-bridge, but overall code quality is pretty alpha.

https://github.com/k-bx/servant-elm

Example CRUD I'm using as a basis: https://github.com/k-bx/servant-elm-generically

[domenkozar]

Maybe we could maintain this at https://github.com/haskell-servant/servant-elm as a community?

[k-bx]

Would be happy to, would you kick-off the process? Also, any thoughts on moving to elm-bridge?

[domenkozar]

@k-bx see https://github.com/mattjbray/servant-elm/pull/43 - I'm for it. Since 0.19 breaks backwards compatibility it seems like a good time to use elm-bridge.

@alpmestan @mattjbray - what do you think about moving servant-elm to haskell-servant?

[alpmestan]

I personally wouldn't mind, as long as some people volunteer to maintain it, since @phadej and I have quite a lot on our plates already =)

[domenkozar]

I can help with maintenance, but we'd need another 1-2 co-maintainers.

[k-bx]

I could definitely co-maintain. I've started using my fork in my side-project yesterday, while it already unveiled few substantial problems, it's working ok with few hacks, and I later plan to use it on my main work project (which is much bigger and needs better lib quality).

[k-bx]

FYI, I've also just migrated my open-source side-project from pure elm-bridge to my fork to generate the Api.elm https://gitlab.com/k-bx/meetup/commit/a91c6fcc3ee6a8c900a265fc09a3cf99eecbbeb9

I think it could be a good project to use for our "real-world usage" purposes as we go. Website is at https://meetup.events, code at https://gitlab.com/k-bx/meetup

[mattjbray]

@domenkozar I'm happy to transfer this repo to haskell-servant. In the meantime I've added you to this repo. Unfortunately I've not had a lot of Haskell projects recently so I haven't been giving servant-elm the attention it deserves :)

Feel free to take the 0.19 update and migration to elm-bridge forward.

[k-bx]

@mattjbray more importantely, please add @domenkozar as a library maintainer on Hackage (feel free to add me as well, my nick is k_bx)

[mattjbray]

@k-bx Done.

@domenkozar @alpmestan let me know about moving the repo to haskell-servant.

[alpmestan]

Where is it again that we can move projects to other orgs, isn't it in this project's settings?

Let me know if there's anything I need to do on the "haskell-servant side".

[szg251]

@domenkozar I am also happy to help if I can.

[domenkozar]

Thanks all :) I'll add @mattjbray, @gege251, @k-bx and me as maintainers and to the README once we do the transfer.

[domenkozar]

Superseded by https://github.com/haskell-servant/servant-elm/pull/49