-- | This module defines the `MonadTrans` type class of _monad transformers_.

module Control.Monad.Trans.Class where

import Prelude (class Monad)

-- | The `MonadTrans` type class represents _monad transformers_.
-- |
-- | A monad transformer is a type constructor of kind `(* -> *) -> * -> *`, which
-- | takes a `Monad` as its first argument, and returns another `Monad`.
-- |
-- | This allows us to add additional effects to an existing monad. By iterating this
-- | process, we create monad transformer _stacks_, which contain all of the effects
-- | required for a particular computation.
-- |
-- | The laws state that `lift` is a `Monad` morphism.
-- |
-- | Laws:
-- |
-- | - `lift (pure a) = pure a`
-- | - `lift (do { x <- m ; y }) = do { x <- lift m ; lift y }`
class MonadTrans t where
  lift :: forall m a. Monad m => m a -> t m a