Servant, powered by a free monad with cookies handled in a cross cutting way.

servant-cookie.hs

type Cookie = Maybe Text

-- 'myAppExecutor' is the brains of the server where all the magic happens.
serverMonadToHandler' :: ServerResources -> Cookie -> forall a. ServerMonad a -> Handler a
serverMonadToHandler' resources cookie serverMonad = foldFree (myAppExecutor resources cookie) serverMonad

serverMonadToHandler :: ServerResources -> Cookie -> ServerMonad :~> Handler
serverMonadToHandler resources cookie = Nat $ serverMonadToHandler' resources cookie

-- 'MyAppApi' is the type that represents the endpoints handled by this server.
type ApiWithCookie = Header "Cookie" Text :> MyAppApi

apiWithCookieProxy :: Proxy ApiWithCookie
apiWithCookieProxy = Proxy

myAppServerT :: ServerT MyAppApi ServerMonad
myAppServerT  = homepageHandler
              :<|> searchHandler
              :<|> searchPageHandler

myAppServer :: ServerResources -> Server ApiWithCookie
myAppServer resources cookie = enter (serverMonadToHandler resources cookie) myAppServerT

myAppApplication :: ServerResources -> Application
myAppApplication resources = serve apiWithCookieProxy (myAppServer resources)