Example for JSON decoders

[MattiaVerticchio]

Hi, and thanks for making elm-codegen! 😁

If I understood correctly, one of its goals is boilerplate or repetitive code generation, such as JSON codecs or encoders-decoders. However, It isn’t clear how to use regular Elm types to generate an encoder or decoder, and it would be really helpful to have this common use case in the docs.

Is it possible to add an example to the README.md?

[simonh1000]

Seconded I've been trying a couple of hours and got to

renderFile =
    let
        anonFn : Expression -> Expression
        anonFn _ =
            Elm.fn ( "name", Nothing )
                (\firstArgument -> Elm.record [ ( "name", firstArgument ) ])

        setter =
            Elm.Declare.value "decodeHighlight"
                (Gen.Json.Decode.map anonFn Gen.Json.Decode.string)
    in
    Elm.file [ "MyFile" ]
        [ setter.declaration
        ]

but that generates

decodeHighlight : Json.Decode.Decoder (name -> { name : name })
decodeHighlight =
    Json.Decode.map (\mapUnpack -> \name -> { name = name }) Json.Decode.string

which is \mapUnpack -> too much