does it work?

src/Application.hs

@@ -43,6 +43,7 @@ import System.Log.FastLogger                (defaultBufSize, newStdoutLoggerSet,
 import Handler.Common
 import Handler.Home
 import Handler.Station
+import Handler.Ad
 
 -- This line actually creates our YesodDispatch instance. It is the second half
 -- of the call to mkYesodData which occurs in Foundation.hs. Please see the

src/Foundation.hs

@@ -146,8 +146,10 @@ instance Yesod App where
         -- value passed to hamletToRepHtml cannot be a widget, this allows
         -- you to use normal widget features in default-layout.
 
+        -- randomAddNumber <- liftIO $ getStdRandom (randomR (0,4))
+
         pc <- widgetToPageContent $ do
-            addStylesheet $ StaticR css_bootstrap_css
+            -- addStylesheet $ StaticR css_bootstrap_css
                                     -- ^ generated from @Settings/StaticFiles.hs@
             $(widgetFile "default-layout")
         withUrlRenderer $(hamletFile "templates/default-layout-wrapper.hamlet")

src/Handler/Ad.hs

@@ -0,0 +1,15 @@
+{-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeApplications #-}
+module Handler.Ad where
+
+import Import
+
+getAdR :: Handler Html
+getAdR = do
+  basePath <- getsYesod (appAdFilePath . appSettings)
+  number <- applyAtomicGen (randomR (0 :: Int ,4)) globalStdGen
+  sendFile typePng $ basePath <> "image" <> show number <> ".png"

src/Handler/Station.hs

@@ -19,7 +19,8 @@ checkStation stationIdentifier = do
     Nothing -> notFound
     Just m  -> return m
 
-repsertBy :: (MonadIO m, PersistUniqueRead backend, PersistRecordBackend record backend, AtLeastOneUniqueKey record, SafeToInsert record)  => record -> ReaderT backend m ()
+-- TODO works without the type annotation, but I don't know why this one is wrong. No time to find out now
+-- repsertBy :: (MonadIO m, PersistUniqueRead backend, PersistRecordBackend record backend, AtLeastOneUniqueKey record, SafeToInsert record)  => record -> ReaderT backend m ()
 repsertBy val = do
   valM <- getByValue val
   case valM of

src/Import/NoFoundation.hs

@@ -10,3 +10,5 @@ import Settings.StaticFiles  as Import
 import Yesod.Auth            as Import
 import Yesod.Core.Types      as Import (loggerSet)
 import Yesod.Default.Config2 as Import
+import System.Random         as Import
+import System.Random.Stateful as Import

src/Settings.hs

@@ -71,6 +71,7 @@ data AppSettings = AppSettings
     -- ^ Copyright text to appear in the footer of the page
 
     , appStations :: Map Text Text
+    , appAdFilePath :: String
     }
 
 instance FromJSON AppSettings where
@@ -98,6 +99,7 @@ instance FromJSON AppSettings where
 
         appCopyright              <- o .:  "copyright"
         appStations               <- M.fromList . map (\x -> (stationId x, stationName x)) <$> o .:  "stations"
+        appAdFilePath             <- o .: "ad-files"
 
         return AppSettings {..}