This is bad elm code I wrote.

Main.elm

import StartApp.Simple as StartApp
import Html exposing (..)
import Html.Attributes exposing (..)
import Html.Events exposing (..)
import Signal exposing (Address)
import Json.Decode as Json

main =
  StartApp.start { model = model, view = view, update = update }


model = 
  {
    naughtyField = "",
    niceField = "",
    naughty = ["Joe"],
    nice = ["Merrick"]
  }

person item = 
  div []
    [text item] 

people list =
  div []
    (List.map person list)

xmaslist address field list title action updateAction =
  div []
    [ h1 [] [text title]
    , input 
       [
        type' "text"
        , value field
        , onEnter address action field 
        , onInput address updateAction
       ] []
    , people list
    ]

onEnter address value field =
  on "keydown"
    (Json.customDecoder keyCode is13)
    (\_ -> Signal.message address (value field))

onInput address value =
  on "input" targetValue (\str -> Signal.message address (value str))

is13 code =
  if code == 13 then Ok () else Err "not the right key code"

view address model = 
  div []
    [xmaslist address model.naughtyField model.naughty "Naughty" AddToNaughty UpdateNaughtyField, xmaslist address model.niceField model.nice "Nice" AddToNice UpdateNiceField]

type Action 
  = AddToNaughty String
  | AddToNice String
  | UpdateNiceField String
  | UpdateNaughtyField String

update action model =
  case action of
    AddToNice name -> 
      { model | 
        niceField = "",
        nice = model.nice ++ [name]
      }
    AddToNaughty name -> 
      { model | 
        naughtyField = "",
        naughty = model.naughty ++ [name]
      }
    UpdateNiceField name ->
      { model | 
        niceField = name
      }
    UpdateNaughtyField name ->
      {
        model |
        naughtyField = name
      }