Copyright	(C) 2008-2013 Edward Kmett
License	BSD-style (see the file LICENSE)
Maintainer	Edward Kmett <ekmett@gmail.com>
Stability	provisional
Portability	portable
Safe Haskell	Safe
Language	Haskell2010

Control.Comonad.Trans.Env

Contents

The strict environment comonad
The strict environment comonad transformer
Combinators

Description

The environment comonad holds a value along with some retrievable context.

This module specifies the environment comonad transformer (aka coreader), which is left adjoint to the reader comonad.

The following sets up an experiment that retains its initial value in the background:

>>> let initial = env 0 0

Extract simply retrieves the value:

>>> extract initial
0

Play around with the value, in our case producing a negative value:

>>> let experiment = fmap (+ 10) initial
>>> extract experiment
10

Oh noes, something went wrong, 10 isn't very negative! Better restore the initial value using the default:

>>> let initialRestored = experiment =>> ask
>>> extract initialRestored
0

Synopsis

The strict environment comonad

type Env e = EnvT e Identity #

env :: e -> a -> Env e a #

Create an Env using an environment and a value

runEnv :: Env e a -> (e, a) #

The strict environment comonad transformer

data EnvT e w a #

Constructors

EnvT e (w a)

Instances

Comonad w => ComonadEnv e (EnvT e w) #
Methods ask :: EnvT e w a -> e #
ComonadStore s w => ComonadStore s (EnvT e w) #
Methods pos :: EnvT e w a -> s # peek :: s -> EnvT e w a -> a # peeks :: (s -> s) -> EnvT e w a -> a # seek :: s -> EnvT e w a -> EnvT e w a # seeks :: (s -> s) -> EnvT e w a -> EnvT e w a # experiment :: Functor f => (s -> f s) -> EnvT e w a -> f a #
ComonadTraced m w => ComonadTraced m (EnvT e w) #
Methods trace :: m -> EnvT e w a -> a #
ComonadHoist (EnvT e) #
Methods cohoist :: (Comonad w, Comonad v) => (forall x. w x -> v x) -> EnvT e w a -> EnvT e v a #
ComonadTrans (EnvT e) #
Methods lower :: Comonad w => EnvT e w a -> w a #
Functor w => Functor (EnvT e w) #
Methods fmap :: (a -> b) -> EnvT e w a -> EnvT e w b # (<$) :: a -> EnvT e w b -> EnvT e w a #
(Monoid e, Applicative m) => Applicative (EnvT e m) #
Methods pure :: a -> EnvT e m a # (<>) :: EnvT e m (a -> b) -> EnvT e m a -> EnvT e m b # (>) :: EnvT e m a -> EnvT e m b -> EnvT e m b # (<*) :: EnvT e m a -> EnvT e m b -> EnvT e m a #
Foldable w => Foldable (EnvT e w) #
Methods fold :: Monoid m => EnvT e w m -> m # foldMap :: Monoid m => (a -> m) -> EnvT e w a -> m # foldr :: (a -> b -> b) -> b -> EnvT e w a -> b # foldr' :: (a -> b -> b) -> b -> EnvT e w a -> b # foldl :: (b -> a -> b) -> b -> EnvT e w a -> b # foldl' :: (b -> a -> b) -> b -> EnvT e w a -> b # foldr1 :: (a -> a -> a) -> EnvT e w a -> a # foldl1 :: (a -> a -> a) -> EnvT e w a -> a # toList :: EnvT e w a -> [a] # null :: EnvT e w a -> Bool # length :: EnvT e w a -> Int # elem :: Eq a => a -> EnvT e w a -> Bool # maximum :: Ord a => EnvT e w a -> a # minimum :: Ord a => EnvT e w a -> a # sum :: Num a => EnvT e w a -> a # product :: Num a => EnvT e w a -> a #
Traversable w => Traversable (EnvT e w) #
Methods traverse :: Applicative f => (a -> f b) -> EnvT e w a -> f (EnvT e w b) # sequenceA :: Applicative f => EnvT e w (f a) -> f (EnvT e w a) # mapM :: Monad m => (a -> m b) -> EnvT e w a -> m (EnvT e w b) # sequence :: Monad m => EnvT e w (m a) -> m (EnvT e w a) #
(Semigroup e, ComonadApply w) => ComonadApply (EnvT e w) #
Methods (<@>) :: EnvT e w (a -> b) -> EnvT e w a -> EnvT e w b # (@>) :: EnvT e w a -> EnvT e w b -> EnvT e w b # (<@) :: EnvT e w a -> EnvT e w b -> EnvT e w a #
Comonad w => Comonad (EnvT e w) #
Methods extract :: EnvT e w a -> a # duplicate :: EnvT e w a -> EnvT e w (EnvT e w a) # extend :: (EnvT e w a -> b) -> EnvT e w a -> EnvT e w b #
(Data e, Typeable (* -> *) w, Data (w a), Data a) => Data (EnvT e w a) #
Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> EnvT e w a -> c (EnvT e w a) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (EnvT e w a) # toConstr :: EnvT e w a -> Constr # dataTypeOf :: EnvT e w a -> DataType # dataCast1 :: Typeable (* -> ) t => (forall d. Data d => c (t d)) -> Maybe (c (EnvT e w a)) # dataCast2 :: Typeable ( -> * -> *) t => (forall d b. (Data d, Data b) => c (t d b)) -> Maybe (c (EnvT e w a)) # gmapT :: (forall b. Data b => b -> b) -> EnvT e w a -> EnvT e w a # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> EnvT e w a -> r # gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> EnvT e w a -> r # gmapQ :: (forall d. Data d => d -> u) -> EnvT e w a -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> EnvT e w a -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> EnvT e w a -> m (EnvT e w a) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> EnvT e w a -> m (EnvT e w a) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> EnvT e w a -> m (EnvT e w a) #

runEnvT :: EnvT e w a -> (e, w a) #

lowerEnvT :: EnvT e w a -> w a #

Gets rid of the environment. This differs from extract in that it will not continue extracting the value from the contained comonad.

Combinators

ask :: EnvT e w a -> e #

Retrieves the environment.

asks :: (e -> f) -> EnvT e w a -> f #

Like ask, but modifies the resulting value with a function.

asks = f . ask

local :: (e -> e') -> EnvT e w a -> EnvT e' w a #

Modifies the environment using the specified function.