Simple, high performance logger. The design choice of this logger is biased towards simplicity instead of generlization:

• All log functions lives in IO.
• A logger connected to stderr, setStdLogger are always available.
• Each logging thread are responsible for building log Builders into a small Bytes with line buffer instead of leaving all Builders to the flushing thread so that:
• We won't keep garbage for too long simply because they're referenced by log's Builder.
• Each logging thread only need perform a CAS to prepend log Bytes into a list, which reduces contention.
• Each log is atomic, Logging order is preserved under concurrent settings.

Flushing is automatic and throttled for debug, info, warn to boost performance, while a fatal log always flush logger's buffer, This also lead to a problem that if main thread exits too early logs may missed, to add a flushing when program exits, use withLogger like:

import Std.IO.Logger

main :: IO ()
main = withStdLogger $ do
    ....