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(.module:
[lux #*
[control
["F" functor]
comonad]
[type
implicit]])
(type: #export (Store s a)
{#cursor s
#peek (-> s a)})
(def: (extend f wa)
(All [s a b] (-> (-> (Store s a) b) (Store s a) (Store s b)))
{#cursor (get@ #cursor wa)
#peek (function (_ s) (f (set@ #cursor s wa)))})
(structure: #export Functor<Store> (All [s] (F.Functor (Store s)))
(def: (map f fa)
(extend (function (_ store)
(f (:: store peek (:: store cursor))))
fa)))
(structure: #export CoMonad<Store> (All [s] (CoMonad (Store s)))
(def: functor Functor<Store>)
(def: (unwrap wa) (::: peek (::: cursor)))
(def: split (extend id)))
(def: #export (peeks trans store)
(All [s a] (-> (-> s s) (Store s a) a))
(|> (::: cursor) trans (::: peek)))
(def: #export (seek cursor store)
(All [s a] (-> s (Store s a) (Store s a)))
(:: (::: split store) peek cursor))
(def: #export (seeks change store)
(All [s a] (-> (-> s s) (Store s a) (Store s a)))
(|> store (::: split) (peeks change)))
(def: #export (experiment Functor<f> change store)
(All [f s a] (-> (F.Functor f) (-> s (f s)) (Store s a) (f a)))
(:: Functor<f> map (::: peek) (change (::: cursor))))
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