Control.Comonad.Context

category-extras-0.1: Various modules and constructs inspired by category theory.

Portability	portable
Stability	experimental
Maintainer	dan.doel@gmail.com

Description

Defines the state-in-context comonad, which is dual to the state monad. Each operation in the context comonad runs in a context determined by later operations. (Observe, for example, experiment, which runs the preceeding operations multiple times in different contexts and returns a list of results.)

Synopsis

data Context c a = Context (c -> a) c

get :: Context c a -> c

modify :: (c -> c) -> Context c a -> a

experiment :: [c -> c] -> Context c a -> [a]

liftCtx :: (a -> b) -> Context c a -> b

Documentation

data Context c a

Source

Constructors

Context (c -> a) c

Instances

Functor (Context c)

Comonad (Context c)

get :: Context c a -> c

Source

Returns the context

modify :: (c -> c) -> Context c a -> a

Source

Returns the result of the preceeding operations running in a modified context

experiment :: [c -> c] -> Context c a -> [a]

Source

Returns a list of results created by running prior operations in modified contexts created by the list of context-modifiers.

liftCtx :: (a -> b) -> Context c a -> b

Source

Lifts an operation into the context comonad. Syntactic sugar for fmap when chaining comonad operations.

  liftCtx         == extract . fmap f
  w =>> liftCtx f == fmap f w

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