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(.module:
lux
(lux [io #+ IO io]
[function]
(control [functor #+ Functor]
[apply #+ Apply]
[monad #+ do Monad])
(data [product])
(concurrency [atom #+ Atom atom])
(type abstract)))
(def: #export parallelism
Nat
("lux process parallelism"))
(abstract: #export (Promise a)
{#.doc "Represents values produced by asynchronous computations (unlike IO, which is synchronous)."}
(Atom [(Maybe a) (List (-> a (IO Top)))])
(def: #export (promise ?value)
(All [a] (-> (Maybe a) (Promise a)))
(@abstraction (atom [?value (list)])))
(def: #export (poll (^@representation promise))
{#.doc "Polls a promise's value."}
(All [a] (-> (Promise a) (Maybe a)))
(|> (atom.read promise)
io.run
product.left))
(def: #export (resolve value (^@representation promise))
{#.doc "Sets an promise's value if it has not been done yet."}
(All [a] (-> a (Promise a) (IO Bool)))
(do io.Monad<IO>
[(^@ old [_value _observers]) (atom.read promise)]
(case _value
(#.Some _)
(wrap false)
#.None
(do @
[#let [new [(#.Some value) #.None]]
succeeded? (atom.compare-and-swap old new promise)]
(if succeeded?
(do @
[_ (monad.map @ (function (_ f) (f value))
_observers)]
(wrap true))
(resolve value (@abstraction promise)))))))
(def: #export (await f (^@representation promise))
(All [a] (-> (-> a (IO Top)) (Promise a) Top))
(let [(^@ old [_value _observers]) (io.run (atom.read promise))]
(case _value
(#.Some value)
(io.run (f value))
#.None
(let [new [_value (#.Cons f _observers)]]
(if (io.run (atom.compare-and-swap old new promise))
[]
(await f (@abstraction promise)))))))
)
(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))
(struct: #export _ (Functor Promise)
(def: (map f fa)
(let [fb (promise #.None)]
(exec (await (function (_ a) (resolve (f a) fb))
fa)
fb))))
(struct: #export _ (Apply Promise)
(def: functor Functor<Promise>)
(def: (apply ff fa)
(let [fb (promise #.None)]
(exec (await (function (_ f)
(io (await (function (_ a) (resolve (f a) fb))
fa)))
ff)
fb))))
(struct: #export _ (Monad Promise)
(def: functor Functor<Promise>)
(def: (wrap a)
(promise (#.Some a)))
(def: (join mma)
(let [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 #.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 #.None)]
(`` (exec (~~ (do-template [<promise>]
[(await (function (_ value) (resolve value left||right))
<promise>)]
[left]
[right]))
left||right))))
(def: #export (schedule millis-delay computation)
{#.doc "Runs an I/O computation on its own process (after a specified delay) and returns a Promise that will eventually host its result."}
(All [a] (-> Nat (IO a) (Promise a)))
(let [!out (promise #.None)]
(exec ("lux process schedule" millis-delay
(io (io.run (resolve (io.run computation)
!out))))
!out)))
(def: #export future
{#.doc "Runs an I/O computation on its own process and returns a Promise that will eventually host its result."}
(All [a] (-> (IO a) (Promise a)))
(schedule +0))
(def: #export (delay time-millis value)
{#.doc "Delivers a value after a certain period has passed."}
(All [a] (-> Nat a (Promise a)))
(schedule time-millis (io value)))
(def: #export (wait time-millis)
{#.doc "Returns a promise that will be resolved after the specified amount of milliseconds."}
(-> Nat (Promise Top))
(delay time-millis []))
(def: #export (time-out time-millis 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-millis) promise))
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