Hello, To analyse, test, and debug my system I use a WriterT for logging. The log file created can be quite large and a lot of 'Log' is created in memory, too. I thought, that maybe I can (ab)use the compiler to switch logging on and off as needed before compiling. I tried to either always return an empty Log when running the WriterT, or just always ignore logging depending on a constant and hoped GHC to optimize the logging away. _NOLOGGING = True runWT :: (Monad m) => (WriterT Log m a) -> m (a, Log) runWT m | _NOLOGGING = runWriterT m empty >>= \(a,_) -> return (a,emptyLog ) | otherwise = runWriterT m emptyLog logging :: Message -> WriterT Log m () logging msg = if _NOLOGGING then return () else tell msg However, according to the heap profile there is still a lot of 'Log' in the memory. So, is this possible this way at all and if not, is there another (apart from removing all logging by hand). Thanks