User.elm

-- when someone wants to use our widget
-- they don't need to know any facts about anything!

import Update (step)
import Model (initialize)
import View (view)

-- nothing gives access to any details, and things
-- will work as they need to. One trick here is to
-- make sure the view function takes a (Handle Action)
-- as an argument such that it can be wired up later.

WidgetModel.elm

module Model (initialize) where

import UnderlyingModel (..)

initialize : Int -> ... -> State

noop : Action

WidgetUnderlyingModel.elm

module UnderlyingModel where

type State = { count:Int, ... }
data Action = ...

WidgetUpdate.elm

module Update (step) where

import UnderlyingModel (..)

step : Action -> State -> State

WidgetView.elm

module View (view) where

import UnderlyingModel (..)

view : Handle Action -> State -> Element