Add MonadTrans

[treeowl]

I don't see anything for MonadTrans. I recommend using this base monad for testing it:

data TestF a = TestF !Int [a]
  deriving (Functor, Eq, Show)
newtype TestM a = TestM (Free TestF a)

where it's easier to define a Free monad locally (with lots of StandaloneDeriving) than to do the Show1, Eq1, etc., gunk needed to use the one in Free.

[treeowl]

Of course, you could also unpack TestF into the free monad for efficiency. Dunno if it's worth the loss of clarity.

[andrewthad]

I'm fine with this if anyone wants to implement it. I'm not terribly concerned about efficiency or even about the particular implementation, as long as it works.

[treeowl]

I can try, though I'm not really familiar with the way things are done in this package. MonadTrans properties are really just the most basic one might want for lift. I have much less of a clue about how one might effectively test that it lifts MonadReader, MonadError, etc., properties correctly.