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(.module:
[library
[lux (#- and or)
[abstract
[functor (#+ Functor)]
[apply (#+ Apply)]
["." monad (#+ Monad do)]]
[control
[pipe (#+ case>)]
["." function]
["." io (#+ IO io)]]
[data
["." product]]
[type (#+ :sharing)
abstract]]]
[//
["." thread]
["." atom (#+ Atom atom)]])
(abstract: #export (Async a)
(Atom [(Maybe a) (List (-> a (IO Any)))])
{#.doc "Represents values produced by asynchronous computations (unlike IO, which is synchronous)."}
(type: #export (Resolver a)
{#.doc (doc "The function used to give a value to an async."
"Will signal 'true' if the async has been resolved for the 1st time, 'false' otherwise.")}
(-> a (IO Bit)))
(def: (resolver async)
{#.doc "Sets an async's value if it has not been done yet."}
(All [a] (-> (Async a) (Resolver a)))
(function (resolve value)
(let [async (:representation async)]
(do {! io.monad}
[(^@ old [_value _observers]) (atom.read async)]
(case _value
(#.Some _)
(in #0)
#.None
(do !
[#let [new [(#.Some value) #.None]]
succeeded? (atom.compare_and_swap old new async)]
(if succeeded?
(do !
[_ (monad.map ! (function (_ f) (f value))
_observers)]
(in #1))
(resolve value))))))))
(def: #export (resolved value)
{#.doc (doc "Produces an async that has already been resolved to the given value.")}
(All [a] (-> a (Async a)))
(:abstraction (atom [(#.Some value) (list)])))
(def: #export (async _)
{#.doc (doc "Creates a fresh async that has not been resolved yet.")}
(All [a] (-> Any [(Async a) (Resolver a)]))
(let [async (:abstraction (atom [#.None (list)]))]
[async (..resolver async)]))
(def: #export poll
{#.doc "Polls an async for its value."}
(All [a] (-> (Async a) (IO (Maybe a))))
(|>> :representation
atom.read
(\ io.functor map product.left)))
(def: #export (await f async)
{#.doc (doc "Executes the given function as soon as the async has been resolved.")}
(All [a] (-> (-> a (IO Any)) (Async a) (IO Any)))
(do {! io.monad}
[#let [async (:representation async)]
(^@ old [_value _observers]) (atom.read async)]
(case _value
(#.Some value)
(f value)
#.None
(let [new [_value (#.Item f _observers)]]
(do !
[swapped? (atom.compare_and_swap old new async)]
(if swapped?
(in [])
(await f (:abstraction async))))))))
)
(def: #export resolved?
{#.doc "Checks whether an async's value has already been resolved."}
(All [a] (-> (Async a) (IO Bit)))
(|>> ..poll
(\ io.functor map
(|>> (case> #.None
#0
(#.Some _)
#1)))))
(implementation: #export functor
(Functor Async)
(def: (map f fa)
(let [[fb resolve] (..async [])]
(exec (io.run (..await (|>> f resolve) fa))
fb))))
(implementation: #export apply
(Apply Async)
(def: &functor ..functor)
(def: (apply ff fa)
(let [[fb resolve] (..async [])]
(exec (io.run (..await (function (_ f)
(..await (|>> f resolve) fa))
ff))
fb))))
(implementation: #export monad
(Monad Async)
(def: &functor ..functor)
(def: in ..resolved)
(def: (join mma)
(let [[ma resolve] (async [])]
(exec (io.run (..await (..await resolve) mma))
ma))))
(def: #export (and left right)
{#.doc (doc "Combines the results of both asyncs, in-order.")}
(All [a b] (-> (Async a) (Async b) (Async [a b])))
(let [[read! write!] (:sharing [a b]
[(Async a) (Async b)]
[left right]
[(Async [a b])
(Resolver [a b])]
(..async []))
_ (io.run (..await (function (_ left)
(..await (function (_ right)
(write! [left right]))
right))
left))]
read!))
(def: #export (or left right)
{#.doc (doc "Yields the results of whichever async gets resolved first."
"You can tell which one was resolved first through pattern-matching.")}
(All [a b] (-> (Async a) (Async b) (Async (Or a b))))
(let [[a|b resolve] (..async [])]
(with_expansions
[<sides> (template [<async> <tag>]
[(io.run (await (|>> <tag> resolve) <async>))]
[left #.Left]
[right #.Right]
)]
(exec <sides>
a|b))))
(def: #export (either left right)
{#.doc (doc "Yields the results of whichever async gets resolved first."
"You cannot tell which one was resolved first.")}
(All [a] (-> (Async a) (Async a) (Async a)))
(let [[left||right resolve] (..async [])]
(`` (exec (~~ (template [<async>]
[(io.run (await resolve <async>))]
[left]
[right]))
left||right))))
(def: #export (schedule millis_delay computation)
{#.doc (doc "Runs an I/O computation on its own thread (after a specified delay)."
"Returns a aromise that will eventually host its result.")}
(All [a] (-> Nat (IO a) (Async a)))
(let [[!out resolve] (..async [])]
(exec (|> (do io.monad
[value computation]
(resolve value))
(thread.schedule millis_delay)
io.run)
!out)))
(def: #export future
{#.doc (doc "Runs an I/O computation on its own thread."
"Returns an async that will eventually host its result.")}
(All [a] (-> (IO a) (Async a)))
(..schedule 0))
(def: #export (delay time_millis value)
{#.doc "Delivers a value after a certain period has passed."}
(All [a] (-> Nat a (Async a)))
(..schedule time_millis (io value)))
(def: #export (wait time_millis)
{#.doc "Returns an async that will be resolved after the specified amount of milliseconds."}
(-> Nat (Async Any))
(..delay time_millis []))
(def: #export (time_out time_millis async)
{#.doc "Wait for an async to be resolved within the specified amount of milliseconds."}
(All [a] (-> Nat (Async a) (Async (Maybe a))))
(..or (wait time_millis) async))
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