Convenient ways to work with mtl stack

[chshersh]

It's very inconvenient to use flip runReaderT r or (runReaderT r) to run monads from mtl stack because first argument of such functions is monad, not environment. I propose to add next functions:

usingReaderT :: r -> ReaderT r m a -> m a
usingReader  :: r -> Reader r a -> a

usingStateT :: s -> StateT s m a -> m a
usingState  :: s -> State s a -> a

Maybe it's better to somehow force introduction of such functions directly inside mtl.

[gromakovsky]

usingStateT :: s -> StateT s m a -> m a

It's questionable what this function should return. It can be analogue of runStateT, execStateT, evalStateT.

[chshersh]

@gromakovsky Agree. But by our convention (also works good with ReaderT) it returns m a. And in that case we need to introduce new nice names.

[gromakovsky]

Well, this convention is not obvious, another possible convention can be that using is flip run. I can't say that one is better than another one though.