Control.Comonad.Trans.Store.Memo

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

 x = put (get x) x
 y = get (put y x)
 put y x = put y (put z x)

This version of the transformer lazily memoizes the result of applying the comonad to the current state. This can be useful for avoiding redundant computation if you reuse the same StoreT object multiple times.

The Store comonad

type Store s = StoreT s Identity

store :: (s -> a) -> s -> Store s a

runStore :: Store s a -> (s -> a, s)

The Store comonad transformer

data StoreT s w a

Instances

ComonadTrans (StoreT s)

ComonadHoist (StoreT s)

Functor w => Functor (StoreT s w)

(Typeable s, Typeable1 w) => Typeable1 (StoreT s w)

Comonad w => Comonad (StoreT s w)

Extend w => Extend (StoreT s w)

(Typeable s, Typeable1 w, Typeable a) => Typeable (StoreT s w a)

storeT :: Functor w => w (s -> a) -> s -> StoreT s w a

runStoreT :: StoreT s w a -> (w (s -> a), s)

Operations

get :: StoreT s w a -> s

put :: Comonad w => s -> StoreT s w a -> a

modify :: Comonad w => (s -> s) -> StoreT s w a -> a

experiment :: (Comonad w, Functor f) => f (s -> s) -> StoreT s w a -> f a