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| data Store s a = Store (s -> a) s | |
| instance Comonad (Store s) where | |
| extract :: Store s a -> a | |
| extract (Store f s) = f s | |
| -- "replacing all values with containers, and then consuming those containers again" | |
| extend :: Store s a -> (Store s a -> b) -> Store s b | |
| extend s f = fmap f $ duplicate s | |
| -- verbose: Store (\x -> f' $ Store f x) s | |
| duplicate :: Store s a -> Store s (Store s a) | |
| duplicate (Store f s) = Store (\x -> Store f x) s | |
| -- Read out the store at some specific position | |
| peek :: s -> Store s a -> a | |
| peek s (Store f _) = f s | |
| -- Modify the current focus, and read the store using the new focus. | |
| peeks :: (s -> s) -> Store s a -> a | |
| peeks f (Store f' s) = f' (f s) | |
| -- Set the current focus | |
| seek :: s -> Store s a -> Store s a | |
| seek s (Store f _) = Store f s | |
| -- Modify the current focus | |
| seeks :: (s -> s) -> Store s a -> Store s a | |
| seeks f (Store f' s) = Store f' (f s) | |
| -- Run an experiment in the store. | |
| experiment :: Functor f => (s -> f s) -> Store s a -> f a | |
| experiment f (Store s a) = fmap s (f a) |
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