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(;module:
lux
(lux (data (coll [list #* "" Functor<List>])
number
text/format)
[io #- run]
function
(control ["F" functor]
["A" applicative]
["M" monad #+ do Monad]
["p" parser])
[macro]
(macro ["s" syntax #+ syntax: Syntax])
(concurrency [atom #+ Atom atom])
))
(def: #export concurrency-level
Nat
("lux process concurrency-level"))
(type: (Promise-State a)
{#value (Maybe a)
#observers (List (-> a (IO Top)))})
(type: #export (Promise a)
{#;doc "Represents values produced by asynchronous computations (unlike IO, which is synchronous)."}
(Atom (Promise-State a)))
(def: #hidden (promise' ?value)
(All [a] (-> (Maybe a) (Promise a)))
(atom {#value ?value
#observers (list)}))
(syntax: #export (promise [type s;any])
{#;doc (doc "Makes an uninitialized Promise (in this example, of Unit)."
(promise Unit))}
(wrap (list (` (: (Promise (~ type))
(promise' #;None))))))
(def: #export (poll promise)
{#;doc "Polls a Promise's value."}
(All [a] (-> (Promise a) (Maybe a)))
(|> (atom;read promise)
io;run
(get@ #value)))
(def: #export (resolved? promise)
{#;doc "Checks whether a Promise's value has already been resolved."}
(All [a] (-> (Promise a) Bool))
(case (poll promise)
#;None
false
(#;Some _)
true))
(def: #export (resolve value promise)
{#;doc "Sets an Promise's value if it has not been done yet."}
(All [a] (-> a (Promise a) (IO Bool)))
(do Monad<IO>
[old (atom;read promise)]
(case (get@ #value old)
(#;Some _)
(wrap false)
#;None
(do @
[#let [new (set@ #value (#;Some value) old)]
succeeded? (atom;compare-and-swap old new promise)]
(if succeeded?
(do @
[_ (M;map @ (function [f] (f value))
(get@ #observers old))]
(wrap true))
(resolve value promise))))))
(def: #export (await f promise)
(All [a] (-> (-> a (IO Top)) (Promise a) Top))
(let [old (io;run (atom;read promise))]
(case (get@ #value old)
(#;Some value)
(io;run (f value))
#;None
(let [new (update@ #observers (|>> (#;Cons f)) old)]
(if (io;run (atom;compare-and-swap old new promise))
[]
(await f promise))))))
(struct: #export _ (F;Functor Promise)
(def: (map f fa)
(let [fb (promise ($ +1))
## fb (promise' #;None)
]
(exec (await (function [a] (resolve (f a) fb))
fa)
fb))))
(struct: #export _ (A;Applicative Promise)
(def: functor Functor<Promise>)
(def: (wrap a)
(atom {#value (#;Some a)
#observers (list)}))
(def: (apply ff fa)
(let [fb (promise ($ +1))
## fb (promise' #;None)
]
(exec (await (function [f]
(io (await (function [a] (resolve (f a) fb))
fa)))
ff)
fb))
))
(struct: #export _ (Monad Promise)
(def: applicative Applicative<Promise>)
(def: (join mma)
(let [ma (promise ($ +0))
## ma (promise' #;None)
]
(exec (await (function [ma']
(io (await (function [a'] (resolve a' ma))
ma')))
mma)
ma))))
(def: #export (seq left right)
{#;doc "Sequencing combinator."}
(All [a b] (-> (Promise a) (Promise b) (Promise [a b])))
(do Monad<Promise>
[a left
b right]
(wrap [a b])))
(def: #export (alt left right)
{#;doc "Heterogeneous alternative combinator."}
(All [a b] (-> (Promise a) (Promise b) (Promise (| a b))))
(let [a|b (promise (| ($ +0) ($ +1)))
## a|b (promise' #;None)
]
(with-expansions
[<sides> (do-template [<promise> <tag>]
[(await (function [value] (resolve (<tag> value) a|b))
<promise>)]
[left #;Left]
[right #;Right]
)]
(exec <sides>
a|b))))
(def: #export (either left right)
{#;doc "Homogeneous alternative combinator."}
(All [a] (-> (Promise a) (Promise a) (Promise a)))
(let [left||right (promise ($ +0))
## left||right (promise' #;None)
]
(`` (exec (~~ (do-template [<promise>]
[(await (function [value] (resolve value left||right))
<promise>)]
[left]
[right]))
left||right))))
(def: #export (future computation)
{#;doc "Runs an I/O computation on its own process and returns an Promise that will eventually host its result."}
(All [a] (-> (IO a) (Promise a)))
(let [!out (promise ($ +0))
## !out (promise' #;None)
]
(exec ("lux process future" (io (io;run (resolve (io;run computation)
!out))))
!out)))
(def: #export (wait time)
{#;doc "Returns a Promise that will be resolved after the specified amount of milliseconds."}
(-> Nat (Promise Unit))
(let [!out (promise Unit)]
(exec ("lux process schedule" time (resolve [] !out))
!out)))
(def: #export (time-out time promise)
{#;doc "Wait for a Promise to be resolved within the specified amount of milliseconds."}
(All [a] (-> Nat (Promise a) (Promise (Maybe a))))
(alt (wait time) promise))
(def: #export (delay time value)
{#;doc "Delivers a value after a certain period has passed."}
(All [a] (-> Nat a (Promise a)))
(:: Functor<Promise> map (const value) (wait time)))
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