Question

如何在Test API模块中对Cmd msg进行模式匹配？

我有一个Test API，可以替代Web服务。

sources : Id -> (Result Http.Error (List Source) -> msg) -> Cmd msg
sources profileId msg =
    [ { platform = "WordPress", username = "bizmonger", linksFound = 0 }
    , { platform = "YouTube", username = "bizmonger", linksFound = 0 }
    , { platform = "StackOverflow", username = "scott-nimrod", linksFound = 0 }
    ]
        |> Result.Ok
        |> msg
        |> Task.succeed
        |> Task.perform identity

问题：

我收到以下代码的编译错误：

addSource : Id -> Source -> (Result Http.Error (List Source) -> msg) -> Cmd msg
addSource profileId source msg =
    let
        result =
            sources profileId msg
    in
        case result of
            Ok sources ->
                (source :: sources)
                    |> Result.Ok
                    |> msg
                    |> Task.succeed
                    |> Task.perform identity

            Err _ ->
                Cmd.none

Ok来源 - ＆gt; ^^^^^^^^^^模式匹配类型的东西：
Result error value
但它实际上要匹配的值是：
Cmd msg

注意：

据我所知，这些函数返回一个Cmd msg，我需要在Cmd msg上进行模式匹配。但是，此代码位于TestAPI模块中，而不是典型的UI模块。因此，我认为我不应该为依赖于此TestAPI模块的UI客户端中已定义的各种消息定义一个有区别的联合。

附录

type alias Source =
    { platform : String, username : String, linksFound : Int }

Answer 1

因为这是关于＆＃34;嘲笑＆＃34;一个API端点，如果你没有触发副作用，我会在命令中不要使用我常用的数据盒数据＆＃34;高谈阔论。

相反，让我建议拆分您的sources功能：

sourceData : List Source
sourceData =
    [ { platform = "WordPress", username = "bizmonger", linksFound = 0 }
    , { platform = "YouTube", username = "bizmonger", linksFound = 0 }
    , { platform = "StackOverflow", username = "scott-nimrod", linksFound = 0 }
    ]


mockResponse : a -> (Result Http.Error a -> msg) -> Cmd msg
mockResponse data tagger =
    Result.Ok data
        |> Task.succeed
        |> Task.perform tagger


sources : Id -> (Result Http.Error (List Source) -> msg) -> Cmd msg
sources profileId msg =
    mockResponse sourceData msg

现在，实现addSource函数变成了一个相当简单的调用：

addSource : Id -> Source -> (Result Http.Error (List Source) -> msg) -> Cmd msg
addSource profileId source msg 
    mockResponse (source :: sourceData) msg

Answer 2

我意识到我还在进行函数式编程。因此，为什么不从核心要素到更多参与者一起组成功能。

因此，我做了以下事情：

addSourceBase : Id -> Source -> List Source
addSourceBase profileId source =
    source :: (profileId |> sourcesBase)


addSource : Id -> Source -> (Result Http.Error (List Source) -> msg) -> Cmd msg
addSource profileId source msg =
    source
        |> addSourceBase profileId
        |> Result.Ok
        |> msg
        |> Task.succeed
        |> Task.perform identity

如何在Test API模块内的Cmd msg上进行模式匹配？

2 个答案: