Haskell High Performance Programming

Logging in Haskell

A final thing we'll consider is more related to I/O than streaming: logging in Haskell applications. Logging is important in any sufficiently important application.

In a small scale, a list- or DList-based WriterT monad is often all that is needed: it's simple and potentially pure (if the underlying monad is pure). However, on a bigger scale it doesn't make sense to store messages in an internal pure data structure. Instead, it's most efficient to write them to disk (or over a network) immediately (likely still using a buffer, though).

Furthermore, it would be nice if the logging functionality could be decoupled from other application code, even reused between different applications.

A popular solution which provides just that ...