Hello Everyone, mtl-2.3 has been released. This release marks the first major version for the library in a long time, and addresses some longstanding issues that have taken years to fix. As a result, this will be a *breaking update* for many. Please review the following changelog notes: * Added instances for Control.Monad.Trans.Writer.CPS and Control.Monad.Trans.RWS.CPS from transformers 0.5.6 and add Control.Monad.Writer.CPS and Control.Monad.RWS.CPS. * Control.Monad.Cont now re-exports evalCont and evalContT. * Add tryError , withError , handleError , and mapError to Control.Monad.Error.Class , and re-export from Control.Monad.Except. * Remove Control.Monad.List and Control.Monad.Error. * Remove instances of deprecated ListT and ErrorT. * Remove re-exports of Error. * Add instances for Control.Monad.Trans.Accum and Control.Monad.Trans.Select ( http://control.monad.trans.select/ ). * Require GHC 8.6 or higher, and cabal-install 3.0 or higher. * Require transformers-0.5.6 or higher. * Add Control.Monad.Accum for the MonadAccum type class, as well as the LiftingAccum deriving helper. * Add Control.Monad.Select ( http://control.monad.select/ ) for the MonadSelect type class, as well as the LiftingSelect deriving helper. A big thank you to all contributors and commentators, and a special thanks to Koz for picking up maintenance so swiftly. Happy hacking, Emily