Consider adding Tagged instance about elm-bridge HOT 9 CLOSED

type alias User  =
   { name: String
   , email: String
   }

jsonDecUser : Json.Decode.Decoder ( User )
jsonDecUser =
   ("name" := Json.Decode.string) >>= \pname ->
   ("email" := Json.Decode.string) >>= \pemail ->
   Json.Decode.succeed {name = pname, email = pemail}

type alias Email = String
type alias User  =
   { name: String
   , email: Email
   }

jsonDecEmail : Json.Decode.Decoder String
jsonDecEmail = Json.Decode.string

jsonDecUser : Json.Decode.Decoder ( User )
jsonDecUser =
   ("name" := Json.Decode.string) >>= \pname ->
   ("email" := jsonDecEmail) >>= \pemail ->
   Json.Decode.succeed {name = pname, email = pemail}

type alias User1  =
   { name1: String
   , email1: String
   }

jsonDecUser1 : Json.Decode.Decoder ( User1 )
jsonDecUser1 =
   ("name1" := Json.Decode.string) >>= \pname1 ->
   ("email1" := Json.Decode.string) >>= \pemail1 ->
   Json.Decode.succeed {name1 = pname1, email1 = pemail1}

jsonEncUser1 : User1 -> Value
jsonEncUser1  val =
   Json.Encode.object
   [ ("name1", Json.Encode.string val.name1)
   , ("email1", Json.Encode.string val.email1)
   ]

type alias User2  =
   { name2: String
   , email2: Email
   }

jsonDecUser2 : Json.Decode.Decoder ( User2 )
jsonDecUser2 =
   ("name2" := Json.Decode.string) >>= \pname2 ->
   ("email2" := jsonDecEmail) >>= \pemail2 ->
   Json.Decode.succeed {name2 = pname2, email2 = pemail2}

jsonEncUser2 : User2 -> Value
jsonEncUser2  val =
   Json.Encode.object
   [ ("name2", Json.Encode.string val.name2)
   , ("email2", jsonEncEmail val.email2)
   ]