iterM analog for FreeT

[ekmett]

iterM analog for FreeT

[fizruk]

Apparantly, forall m. Monad m => t m a gives way more flexibility than MFunctor t => t Identity a.
The reason is that ContT is not actually MFunctor (because m r in (a -> m r) -> m r is in both positive and negative positions), so one cannot turn ContT Identity a into a ContT m a, unless m is isomorphic to Identity.

[fizruk]

After thinking a bit more on this, I've managed to avoid MFunctor and foralled iterM in my code.

This is what I use now:

transform :: (Functor f, Monad m, MonadTrans t, Monad (t m))
    => (f (t m a) -> t m a) -> FreeT f m a -> t m a
transform phi = iterT phi . hoistIterT lift

runT :: (Functor f, MonadFree f m, MonadTrans t, Monad (t m))
    => FreeT f (t m) a -> t m a
runT = iterT wrapT

[fizruk]

transform is now merged in #42 as iterTM, so I close this issue.