Control.Comonad.Store.Pointer

The array-backed store (state-in-context/costate) comonad transformer is subject to the laws:

 x = seek (pos x) x
 y = pos (seek y x)
 seek y x = seek y (seek z x)

Thanks go to Russell O'Connor and Daniel Peebles for their help formulating and proving the laws for this comonad transformer.

This basic version of this transformer first appeared on Dan Piponi's blog at http://blog.sigfpe.com/2008/03/comonadic-arrays.html.

Since this module relies on the non-Haskell 98 arrays package, it is located here instead of in comonad-transformers.

NB: attempting to seek or peek out of bounds will yield an error.

The Pointer comonad

type Pointer i = PointerT i Identity

pointer :: Array i a -> i -> Pointer i a

runPointer :: Pointer i a -> (Array i a, i)

The Pointer comonad transformer

data PointerT i w a

Constructors

PointerT (w (Array i a)) i

Instances

(ComonadEnv m w, Ix i) => ComonadEnv m (PointerT i w)

(Comonad w, Ix i) => ComonadStore i (PointerT i w)

(ComonadTraced m w, Ix i) => ComonadTraced m (PointerT i w)

Ix i => ComonadHoist (PointerT i)

Ix i => ComonadTrans (PointerT i)

(Functor w, Ix i) => Functor (PointerT i w)

(Typeable i, Typeable1 w) => Typeable1 (PointerT i w)

(Comonad w, Ix i) => Comonad (PointerT i w)

(Comonad w, Ix i) => Extend (PointerT i w)

(Typeable i, Typeable1 w, Typeable a) => Typeable (PointerT i w a)

runPointerT :: PointerT i w a -> (w (Array i a), i)

pointerBounds :: (Comonad w, Ix i) => PointerT i w a -> (i, i)

Extract the bounds of the currently focused array

module Control.Comonad.Store.Class