devel/hs-mtl-compat - The NetBSD Packages Collection

This package backports the Control.Monad.Except module from mtl (if using
mtl-2.2.0.1 or earlier), which reexports the ExceptT monad transformer and
the MonadError class.

This package should only be used if there is a need to use the
Control.Monad.Except module specifically. If you just want the mtl class
instances for ExceptT, use transformers-compat instead, since mtl-compat
does nothing but reexport the instances from that package.

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.