Suppose I have the following class of monad transformers:
class (Monad m, Monad (t m)) => MonadT t m where
lift :: m a -> t m a
and several instances of the class:
instance MonadT MT1 where ...
instance MonadT MT2 where ...
. . .
instance MonadT MTn where ...
I obtain a new monad composing monad transformers through the IO monad:
type MyMonad = MT1 (MT2 (... (MTn IO)))
And now, if I want to lift "putStrLn" I must write:
myPutStrLn = lift . lift . ... lift . putStrLn
This works but looks ugly.
The question is:
Is there a way that the system could detect how many
lifts are necessary to select the right function?
Another problem is when some of the monad transformers provide the same
functions, for example, if MTi also provides "putStrLn", How could I tell
the system to select the first "putStrLn" found, or the last?
Thanks, Jose Labra
