Elm：如何在嵌套列表上应用 List.map

Question

这是我用简单的 List Float 完成的基本工作

renderCoordinates : List Float -> Html Msg
renderCoordinates coordinates =
    ol [ type_ "A"]
        (List.map (\coordinate -> li [] [text (String.fromFloat coordinate)]) coordinates)

当谈到 List (List(List Float)) 时，我被卡住了。我想知道我是否可以这样做？

renderCoordinates : List (List(List Float)) -> Html Msg
renderCoordinates coordinates =
    ol [ type_ "A"]
        (List.map (List.map (\coordinate -> li [] [text (String.fromFloat coordinate)]) ) coordinates)

-- List.map (List.map (List.map (\coordinate -> li [] [text (String.fromFloat coordinate)]) ) ) coordinates doesnt work as well

基本上我希望显示 List (List(List Float)) 列表中的每个项目... 感谢您的帮助！

更新

在@Simon 的帮助下我对代码进行了一些修改，使其工作方式如下：

renderCoordinates : List (List (List Float)) -> Html Msg
renderCoordinates coordinates =
    let
        map1 : List (List (List Float)) -> List (Html Msg) 
        map1 lists =
            List.concatMap map2 lists

        map2 : List (List Float) -> List (Html Msg)
        map2 floats =
            List.map (\coordinate -> li [] [ text (Debug.toString coordinate) ]) floats
    in
    ol [ type_ "A" ]
        (map1 coordinates)

这将打印 A: [X, Y]

Answer 1

你需要分部分进行，并在每个阶段连接结果

renderCoordinates : List (List (List Float)) -> Html Msg
renderCoordinates coordinates =
    let
        map1 : List (List Float) -> List (Html Msg)
        map1 lists =
            L.concatMap map2 lists

        map2 : List Float -> List (Html Msg)
        map2 floats =
            List.map (\coordinate -> li [] [ text (String.fromFloat coordinate) ]) floats
    in
    ol [ type_ "A" ]
        (List.concatMap map1 coordinates)

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