This package backports the "Control.Monad.Except" module from @mtl@ (if using @mtl-220.127.116.11@ 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.