This example will tie together a few different ideas. We’ll start with a chat subsite, which allows us to embed a chat widget on any page. We’ll use the HTML5 event source API to handle sending events from the server to the client.

-- @Chat.hs
{-# LANGUAGE OverloadedStrings, TypeFamilies, QuasiQuotes,
             TemplateHaskell, FlexibleInstances, MultiParamTypeClasses,
             FlexibleContexts
  #-}
-- | This module defines a subsite that allows you to insert a chat box on
-- any page of your site. It uses eventsource for sending the messages from
-- the server to the browser.
module Chat where

import Yesod
import Control.Concurrent.Chan (Chan, dupChan, writeChan