Conditional JSON decoder with optional fields

Learn
2

This is a classic case for Json.Decode.andthen

e.g. (untested)

import Json.Decode exposing (...)

decodeRecordType : Decoder RecordType
decodeRecordType =
  (at ["type", "name"] string)
    |> andThen decodeRecordTypeDetails

decodeRecordTypeDetails : String -> Decoder RecordType
decodeRecordTypeDetails name =
  case name of
    "bed" -> decodeBed
    "chair" -> decodeChair
    "stool" -> succeed Stool
    _ -> fail ("unknown record type: " ++ name)
2 Likes