Control.Comonad.Env

type Env e = EnvT e Identity

The Env comonad is a synonym for the EnvT comonad transformer, applied to the Identity monad.

runEnv :: forall a e. Env e a -> Tuple e a

Unwrap a value in the Env comonad.

withEnv :: forall a e2 e1. (e1 -> e2) -> Env e1 a -> Env e2 a

Change the environment type in an Env computation.

mapEnv :: forall b a e. (a -> b) -> Env e a -> Env e b

Change the data type in an Env computation.

env :: forall a e. e -> a -> Env e a

Create a value in context in the Env comonad.

class (ComonadAsk e w) <= ComonadEnv e w | w -> e where

The ComonadEnv type class extends ComonadAsk with a function local f x that allows the value of the local context to be modified for the duration of the execution of action x.

An implementation is provided for EnvT.

Laws:

• ask (local f x) = f (ask x)
• extract (local _ x) = extract a
• extend g (local f x) = extend (g <<< local f) x

Members

• local :: forall a. (e -> e) -> w a -> w a

Instances

• ComonadEnv e (Tuple e)
• (Comonad w) => ComonadEnv e (EnvT e w)

ask :: forall e w a. ComonadAsk e w => w a -> e

asks :: forall w e2 e1. ComonadEnv e1 w => (e1 -> e2) -> w e1 -> e2

Get a value which depends on the environment.

newtype EnvT e w a

The environment comonad transformer.

This comonad transformer extends the context of a value in the base comonad with a global environment of type e.

The ComonadEnv type class describes the operations supported by this comonad.

Constructors

• EnvT (Tuple e (w a))

Instances

• Newtype (EnvT e w a) _
• (Functor w) => Functor (EnvT e w)
• (Extend w) => Extend (EnvT e w)
• (Comonad w) => Comonad (EnvT e w)
• ComonadTrans (EnvT e)

withEnvT :: forall a w e2 e1. (e1 -> e2) -> EnvT e1 w a -> EnvT e2 w a

Change the environment type in an EnvT context.

runEnvT :: forall a w e. EnvT e w a -> Tuple e (w a)

Unwrap a value in the EnvT comonad.

mapEnvT :: forall b a w2 w1 e. (w1 a -> w2 b) -> EnvT e w1 a -> EnvT e w2 b

Change the underlying comonad and data type in an EnvT context.