A way to handle cross-pages shared actions in Elm

Main.elm

module Main exposing (main)

import Model exposing (Model, initialModel)
import Html exposing (Html, div, text, button)
import Html.Events exposing (onClick)
import Shared
import Page

import Debug

-- Update

type Msg
  = SharedMsg Shared.Msg
  | PageMsg Page.Msg

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
  case msg of
    -- To modularize, delegate this to Shared's own update function
    SharedMsg msg ->
      let
          log =
            Debug.log "Shared msg" msg
      in
          ( model, Cmd.none )
          
    -- To modularize, delegate this to Page's own update function
    PageMsg msg ->
      let
          log =
            Debug.log "Page msg" msg
      in
          case msg of
            Page.SharedMsg sharedMsg ->
              update ( SharedMsg sharedMsg ) model
              -- shared messages are sent back to be handled by Shared's update function

            Page.PageSpecificAction ->
              ( model, Cmd.none )

-- View

view : Model -> Html Msg
view model =
  div []
  [ button [ onClick ( SharedMsg Shared.SharedAction ) ] [ text "Shared action from main view" ]
  , Html.map PageMsg ( Page.view model )
  ]


-- Subscriptions

subscriptions : Model -> Sub Msg
subscriptions model =
  Sub.none

-- Main

main : Program Never Model Msg
main =
  Html.program
    { init = init
    , update = update
    , subscriptions = subscriptions
    , view = view
    }

init : ( Model, Cmd Msg )
init =
  ( initialModel, Cmd.none )

Model.elm

module Model exposing (..)

type alias Model =
  {}

initialModel : Model
initialModel =
  {}

Page.elm

module Page exposing (..)

import Html exposing (Html, div, text, button)
import Html.Events exposing (onClick)
import Model exposing (Model)

import Shared

-- Update

type Msg
  = PageSpecificAction
  | SharedMsg Shared.Msg


-- View

view : Model -> Html Msg
view model =
  div []
    [ button [ onClick ( SharedMsg Shared.SharedAction ) ] [ text "Shared action from page view" ]
    , button [ onClick ( PageSpecificAction ) ] [ text "Page action from page view" ]
    ]

Shared.elm

module Shared exposing (..)

-- Update

type Msg
  = SharedAction