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(.module:
[lux #*
[abstract
["." functor (#+ Functor)]
[apply (#+ Apply)]
["." monad (#+ Monad do)]]])
(type: #export (Reader r a)
{#.doc "Computations that have access to some environmental value."}
(-> r a))
(def: #export ask
{#.doc "Get the environment."}
(All [r] (Reader r r))
(function (_ env) env))
(def: #export (local change proc)
{#.doc "Run computation with a locally-modified environment."}
(All [r a] (-> (-> r r) (Reader r a) (Reader r a)))
(|>> change proc))
(def: #export (run env proc)
(All [r a] (-> r (Reader r a) a))
(proc env))
(implementation: #export functor
(All [r] (Functor (Reader r)))
(def: (map f fa)
(function (_ env)
(f (fa env)))))
(implementation: #export apply
(All [r] (Apply (Reader r)))
(def: &functor ..functor)
(def: (apply ff fa)
(function (_ env)
((ff env) (fa env)))))
(implementation: #export monad
(All [r] (Monad (Reader r)))
(def: &functor ..functor)
(def: (wrap x)
(function (_ env) x))
(def: (join mma)
(function (_ env)
(mma env env))))
(implementation: #export (with monad)
{#.doc "Monad transformer for Reader."}
(All [M] (-> (Monad M) (All [e] (Monad (All [a] (Reader e (M a)))))))
(def: &functor (functor.compose ..functor (get@ #monad.&functor monad)))
(def: wrap (|>> (\ monad wrap) (\ ..monad wrap)))
(def: (join eMeMa)
(function (_ env)
(do monad
[eMa (run env eMeMa)]
(run env eMa)))))
(def: #export lift
{#.doc "Lift monadic values to the Reader wrapper."}
(All [M e a] (-> (M a) (Reader e (M a))))
(\ ..monad wrap))
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