todolist-update.elm

type Action = Add
            | InputText String -- New!

update : Action -> Model -> Model
update action model =
  case action of
    Add ->
      let newTodo = ( model.nextID, Todo.init model.addText )
          newTodos = model.todos ++ [ newTodo ]
      in
          { model |
              todos = newTodos,
              nextID = model.nextID + 1
          }
    InputText str -> -- New!
      { model |
          addText = str
      }