CODEWITHSUNDEEP
typestype-inferenceelm
pietro909
pietro909

Reputation: 1861

Type inference in Elm

I just began learning Elm and I got stuck with type annotation issue.

This code works:

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

This one raises a compiler exception:

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

The error is

-- 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.

Upvotes: 0

Views: 265

Answers (1)

marcosh
marcosh

Reputation: 9008

I think you are just missing some brackets at the end...

Your code should be 

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

This is because the input function, as div does, wants in input two lists, one for the attributes, one for the other Html pieces it contains

Upvotes: 2

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