See also https://pvp.haskell.org/faq

1.3.1.0 (minor)

• Evaluate message before taking lock in simple handler (#49)
• Define Typeable, Data, Generic and NFData instances for System.Log.Priority (#43)

1.3.0.0 (major)

• [semantic change] Messages are encoded as UTF-8 (previously the encoding was locale dependent) for the Syslog and Growl backends
• Add support for network-3.0; remove redundant dependency on directory and process