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(;module:
lux
(lux (control ["F" functor]
["A" applicative]
[monad #+ do Monad])))
## [Types]
(type: #export (Reader r a)
{#;doc "Computations that have access to some environmental value."}
(-> r a))
## [Structures]
(struct: #export Functor<Reader> (All [r] (F;Functor (Reader r)))
(def: (map f fa)
(function [env]
(f (fa env)))))
(struct: #export Applicative<Reader> (All [r] (A;Applicative (Reader r)))
(def: functor Functor<Reader>)
(def: (wrap x)
(function [env] x))
(def: (apply ff fa)
(function [env]
((ff env) (fa env)))))
(struct: #export Monad<Reader> (All [r] (Monad (Reader r)))
(def: applicative Applicative<Reader>)
(def: (join mma)
(function [env]
(mma env env))))
## [Values]
(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))
(struct: #export (ReaderT Monad<M>)
{#;doc "Monad transformer for Reader."}
(All [M] (-> (Monad M) (All [e] (Monad (All [a] (Reader e (M a)))))))
(def: applicative (A;compose Applicative<Reader> (get@ #monad;applicative Monad<M>)))
(def: (join eMeMa)
(function [env]
(do Monad<M>
[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<Reader> wrap))
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