Just this morning I upgraded a 3500 line Elm 0.17 project to Elm 0.18. I
wrote down my experience that I will share at a later date but I wanted to
share a suggestion.
My app makes a handful of Http requests. For example I have a user model
and Msgs for when the user logs in or out.
type alias Model =
{ username : String
, fullName : String
, password : String
, email : String
}
type Msg =
| Login
| LoginSucceed Model
| LoginFail Http.Error
| Logout
| LogoutSucceed
| LogoutFail Http.Error
A typical 0.18 Http requests looks like this
performLogin : Model -> Cmd Msg
performLogin user =
let
request =
Http.request
{ method = "POST"
, headers = []
, url = "http://mydomain/login";
, body = Http.jsonBody (userEncoder user)
, expect = Http.expectJson userDecoder
, timeout = Nothing
, withCredentials = False
}
in
Http.send
(\result ->
case result of
Ok user ->
LoginSucceed user
Err err ->
LoginFail err
)
request
The `case result of` part in the Http.send argument is a lot of boilerplate
that I don't like seeing copy/pasted in all of my Http Cmds.
Additionally, in most cases my success Msg takes a payload which is the
model that was decoded from the response and my fail Msg takes the Result's
Http.Error.
I have since created a helper function that looks like this
resultToMsg : (x -> b) -> (a -> b) -> Result x a -> b
resultToMsg errMsg okMsg result =
case result of
Ok a ->
okMsg a
Err err ->
errMsg err
With that helper function my Http Cmds now look like this
performLogin : Model -> Cmd Msg
performLogin user =
let
request =
Http.request
{ method = "POST"
, headers = []
, url = "http://mydomain/login";
, body = Http.jsonBody (userEncoder user)
, expect = Http.expectJson userDecoder
, timeout = Nothing
, withCredentials = False
}
in
Http.send
(resultToMsg LoginFail LoginSucceed)
request
Which results in 4 fewer lines of boilerplate (5 including the whitespace).
I'm terrible at naming things but I propose adding a helper function to
elm-lang/core Result with basically the implementation above but with a
more appropriate name than resultToMsg.
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