Control.Comonad.Trans.Env

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

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

ComonadTraced m w => ComonadTraced m (EnvT e w)

Defined in Control.Comonad.Traced.Class

Methods

trace :: m -> EnvT e w a -> a

ComonadStore s w => ComonadStore s (EnvT e w)

Defined in Control.Comonad.Store.Class

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

Comonad w => ComonadEnv e (EnvT e w)

Defined in Control.Comonad.Env.Class

Methods

ask :: EnvT e w a -> e

ComonadHoist (EnvT e)

Defined in Control.Comonad.Trans.Env

Methods

cohoist :: (Comonad w, Comonad v) => (forall x. w x -> v x) -> EnvT e w a -> EnvT e v a

ComonadTrans (EnvT e)

Defined in Control.Comonad.Trans.Env

Methods

lower :: Comonad w => EnvT e w a -> w a

Functor w => Functor (EnvT e w)

Defined in Control.Comonad.Trans.Env

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)

Defined in Control.Comonad.Trans.Env

Methods

pure :: a -> EnvT e m a

(<*>) :: EnvT e m (a -> b) -> EnvT e m a -> EnvT e m b

liftA2 :: (a -> b -> c) -> EnvT e m a -> EnvT e m b -> EnvT e m c

(*>) :: 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)

Defined in Control.Comonad.Trans.Env

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)

Defined in Control.Comonad.Trans.Env

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)

Defined in Control.Comonad.Trans.Env

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)

Defined in Control.Comonad.Trans.Env

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)

Defined in Control.Comonad.Trans.Env

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 e0. (Data d, Data e0) => c (t d e0)) -> 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.