Monad Transformer - Definition

Definition

A monad transformer consists of:

  1. A type constructor t of kind (* -> *) -> * -> *
  2. Monad operations return and bind (or an equivalent formulation) for all t m where m is a monad, satisfying the monad laws
  3. An additional operation, lift :: m a -> t m a, satisfying the following laws: (the notation `bind` below indicates infix application):
    1. lift . return = return
    2. lift (m `bind` k) = (lift m) `bind` (lift . k)

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