将JSON元组解码为Elm元组

Question

我的JSON如下所示

{ "resp":
    [ [1, "things"]
    , [2, "more things"]
    , [3, "even more things"]
    ]
}

问题是我无法将JSON元组解析为Elm元组:

decodeThings : Decoder (List (Int, String))
decodeThings = field "resp" <| list <| map2 (,) int string

它编译,但运行时,它会抛出

BadPayload "Expecting an Int at _.resp[2] but instead got [3, \"even more things\"]

由于某种原因,它只读取[3, "even more things"]一件事而不是JSON格式的元组.
我怎样才能将我的JSON解析成List (Int, String)？

Answer 1

import Json.Decode as Decode

decodeTuple = 
    Decode.map2 Tuple.pair 
        (Decode.index 0 Decode.int) 
        (Decode.index 1 Decode.string)

最简单的是

Decode.list decodeTuple

然后,正如您所说,列表

import Json.Decode as Decode

decodeTuple = 
    Decode.map2 Tuple.pair 
        (Decode.index 0 Decode.int) 
        (Decode.index 1 Decode.string)

Answer 2

你需要一个解码器,将大小为2的javascript数组转换为大小为2的Elm元组.这是一个示例解码器:

arrayAsTuple2 : Decoder a -> Decoder b -> Decoder (a, b)
arrayAsTuple2 a b =
    index 0 a
        |> andThen (\aVal -> index 1 b
        |> andThen (\bVal -> Json.Decode.succeed (aVal, bVal)))

然后,您可以修改原始示例,如下所示:

decodeThings : Decoder (List (Int, String))
decodeThings = field "resp" <| list <| arrayAsTuple2 int string

(注意,如果有两个以上的元素,我的示例解码器不会失败,但它应该让你指向正确的方向)