Class.hs

-- This module provides two interface MonadReadable and MonadStateful, unlike MonadReader
-- and MonadState, these interfaces do not have functional dependencies, allowing for
-- simple and extensible state and read effects.
module Control.Monad.RS.Class where

-- | A class for monads that can read a value of type 'r'.
-- without the functional dependencies, so you can read different types of values
class Monad m => MonadReadable r m where
  {-# MINIMAL query, local #-}
  -- | Query the monad for a value of type 'r'.
  query :: m r

  -- | Transform the result of a query using a function.
  queries :: (r -> r') -> m r'
  queries f = f <$> query
  {-# INLINE queries #-}

  local :: (r -> r) -> m a -> m a

-- | A class for monads that can maintain a state of type 's'.
-- without the functional dependencies, so you can have different types of states
class Monad m => MonadStateful s m where
  {-# MINIMAL get, put #-}
  -- | Get the current state.
  get :: m s

  gets :: (s -> a) -> m a
  gets f = f <$> get
  {-# INLINE gets #-}

  -- | Set the state to a new value.
  put :: s -> m ()

  -- | Modify the current state using a function.
  modify :: (s -> s) -> m ()
  modify f = do
    s <- get
    put (f s)
  {-# INLINE modify #-}