How to log to terminal using scotty with Intellij (Haskell plugin)?

Question

So I'm having something odd happen. Here's an illustrative code example:

main :: IO ()
main
 = do
     scotty 8000 $ do
       get "/" serve
 where
  serve :: ActionM ()
  serve = do
    liftIO $ print "I'm about to serve a request!"

My message should print to the IntelliJ console whenever I type in "localhost:8000/", but it doesn't. Yet when I comment out the scotty stuff and just have:

main :: IO ()
main
 = do print "Hello World!"

IntelliJ has no problem printing this out. What am I doing wrong? When I use the Windows command prompt to run the executable (e.g. ghc --make to create it, then running it), everything works fine - "I'm about to serve a request!" prints to the command prompt terminal everytime I Type in "localhost:8000/"

Is something in the scotty stack redirecting stdout? Maybe capturing it for logging and emitting it on stderr? I'm not familiar with intellij — jberryman, Jun 03 '17 at 17:00
You were right, it was. Just answered my own question. So annoying... — Enis, Jun 03 '17 at 17:29

score 0 · Accepted Answer · answered Jun 03 '17 at 17:28

Figured it out. Needed to make a logger as follows:

 logger <- mkRequestLogger def {
   outputFormat = CustomOutputFormat (\_ _ _ _ -> "")
   }

so that the resulting code would look like:

main :: IO ()
main
 = do
     logger <- mkRequestLogger def {
       outputFormat = CustomOutputFormat (\_ _ _ _ -> "")
       }
     scotty 8000 $ do
       middleware logger
       -- do stuff here

The CustomOutputFormat ignores all other incoming information, focusing only on what you want to print to the console.

How to log to terminal using scotty with Intellij (Haskell plugin)?

1 Answers1