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(;module:
lux
(lux (data ["R" result])
(control functor
applicative
monad
["ex" exception #+ Exception])
(concurrency ["P" promise])
[macro]
(macro ["s" syntax #+ syntax: Syntax])
))
(type: #export (Task a)
(P;Promise (R;Result a)))
(def: #export (fail error)
(All [a] (-> Text (Task a)))
(:: P;Applicative<Promise> wrap (#R;Error error)))
(def: #export (throw exception message)
(All [a] (-> Exception Text (Task a)))
(fail (exception message)))
(def: #export (return value)
(All [a] (-> a (Task a)))
(:: P;Applicative<Promise> wrap (#R;Success value)))
(def: #export (try computation)
(All [a] (-> (Task a) (Task (R;Result a))))
(:: P;Functor<Promise> map (|>. #R;Success) computation))
(struct: #export _ (Functor Task)
(def: (map f fa)
(:: P;Functor<Promise> map
(function [fa']
(case fa'
(#R;Error error)
(#R;Error error)
(#R;Success a)
(#R;Success (f a))))
fa)))
(struct: #export _ (Applicative Task)
(def: functor Functor<Task>)
(def: wrap return)
(def: (apply ff fa)
(do P;Monad<Promise>
[ff' ff
fa' fa]
(wrap (do R;Monad<Result>
[f ff'
a fa']
(wrap (f a)))))))
(struct: #export _ (Monad Task)
(def: applicative Applicative<Task>)
(def: (join mma)
(do P;Monad<Promise>
[mma' mma]
(case mma'
(#R;Error error)
(wrap (#R;Error error))
(#R;Success ma)
ma))))
(syntax: #export (task [type s;any])
{#;doc (doc "Makes an uninitialized Task (in this example, of Unit)."
(task Unit))}
(wrap (list (` (: (;;Task (~ type))
(P;promise' #;None))))))
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