-- hints found in tests/find.hs
warn = length a `seq` return a ==> listM' a
warn = not (null a) ==> notNull a
warn = not (isLeft a) ==> isRight a
warn
  = unsafePerformIO
      (do putStrLn a
          exitWith (ExitFailure 1))
      ==> exitMessage a
warn = knownExtensions \\ badExtensions ==> defaultExtensions