在Elm中输入推断

Question

我刚刚开始学习Elm而且我遇到了类型注释问题。

此代码有效：

viewInput : String -> Html msg
viewInput myText =
    div [ style [("color","red")] ] [ text myText ]

这会引发编译器异常：

viewInput : String -> Html msg
viewInput myText =
    input [ type' "text", placeholder myText ]

错误是

-- TYPE MISMATCH ------------------------------------------------------ form.elm

The type annotation for `viewInput` does not match its definition.

62| viewInput : String -> Html msg
                ^^^^^^^^^^^^^^^^^^
The type annotation is saying:

    String -> Html a

But I am inferring that the definition has this type:

    String -> List (Html a) -> Html a

Detected errors in 1 module.

Answer 1

我认为你最后只是遗漏了一些括号......

您的代码应为

viewInput : String -> Html msg
viewInput myText =
    input [ type' "text", placeholder myText ] []

这是因为input函数，div确实需要输入两个列表，一个用于属性，一个用于包含的其他Html件