Support decoding and encoding Dicts

[polux]

It would be great if, when fed with a type alias aliasing to a Dict, the tool would produce decoders and encoders that make use of Json.Decode.dict and Json.Encode.object.

[eeue56]

Work involved here:

Dict a b should translate to

convertToTypedDict : Decoder a -> Dict String b -> Dict a b
convertToTypedDict decoder dict =
  Dict.toList dict 
    |> List.filterMap (\(x, y) -> (Json.Decode.decodeString decoder x |> Result.toMaybe, y))
    |> Dict.fromList

decodeDict : Decoder (Dict a b)
decodeDict =
  Json.Decode.dict b
    |> (flip Json.Decode.andThen) (convertToTypedDict)

encodeDict = (b -> Json.Encode.value) -> Dict a b -> Json.Encode.value
encodeDict encoder dict =
  Dict.toList dict 
    |> List.map (\(x, y) -> (toString x, encoder y))
    |> Json.Enocde.object

Might be a bit much since technically in JSON you're only allow strings as names.

[Erudition]

Simply use the one in Json.Encode. Extra!