Answers

1. A monad is a type constructor m with an instance of the Monad type class:

   class Applicative m => Monad m where
     (>>=) :: m a -> (a -> m b) -> m b
     return :: a -> m a
     return = pure
     (>>) :: m a -> m b -> m b
     p >> q = p *> q

   It is subject to three laws:

   return x >>= f = f x
   p >>= return = p
   (p >>= q) >>= r = p >>= (\x -> q x >>= r)

...

Effect	Monad	Primitive Operations
No effect, pure	Identity	-
Failure	Maybe	-
Exceptions, errors	Either e	throwError, catchError
State