@hackage mtl-compat0.1.1

This package backports the Control.Monad.Except module (if using mtl-2.2.0.1 or earlier) and monad class instances for ExceptT from transformers-compat (if using mtl-2.1.3.1 or earlier).

Note that unlike how mtl-2.2 or later works, the Control.Monad.Except module defined in this package exports all of ExceptT's monad class instances. Therefore, you may have to declare import Control.Monad.Except () at the top of your file to get all of the ExceptT instances in scope.