Nework.Wai.Application Semigroup type class instance

WaiSemigroup.hs

   {-# LANGUAGE InstanceSigs #-}
   module Wai.Network.Middleware.WaiSemigroup (WaiApp(..)) where
   import Data.Coerce (coerce)
   import Network.HTTP.Types.Status (status404)
   import Network.Wai (Application, responseStatus)

   newtype WaiApp = WaiApp Application

   instance Semigroup WaiApp where
     (<>) :: WaiApp -> WaiApp -> WaiApp
     (<>) app0 app1 = WaiApp $ \req respond ->
       coerce
         app0
         req
         ( \res ->
             if responseStatus res == status404
               then coerce app1 req respond
               else respond res
         )