I'm about to be away from the internet for ten days, and am happy with this. One question though: isn't it already possible to do what hoist does simply by defining a new RunClient instance for the monad?

@jkarni Maybe, yeah, except that a typeclass instance has to be provided for each target monad, and I think you're pretty much stuck with just one transformation per monad (you'd define the instance for TargetMonad as transformations over the instance of SourceMonad) so it's static. While with hoistClient you get to pick the transformation, and it can be dynamic: partially applying some arguments from some context first and finally transforming the return type of clients.

Not sure whether you were suggesting to refactor the PR in terms of RunClient instead or not, but I'm failing to see the advantages so I'm thinking probably not and that you were just curious. =) (or I might be overlooking something?)

No other feedback? Should we merge?