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(.module:
[library
[lux #*
[abstract
[equivalence (#+ Equivalence)]
[functor (#+ Functor)]
[apply (#+ Apply)]
["." monad (#+ Monad do)]]
[control
["." try (#+ Try)]
["." exception (#+ exception:)]
["." io (#+ IO io)]]
[data
["." maybe ("#\." functor)]]
[type (#+ :sharing)
abstract]]]
[//
["." atom (#+ Atom)]
["." async (#+ Async) ("#\." functor)]])
(type: #export (Channel a)
{#.doc "An asynchronous channel to distribute values."}
(Async (Maybe [a (Channel a)])))
(exception: #export channel_is_already_closed)
(interface: #export (Sink a)
{#.doc (doc "The tail-end of a channel, which can be written-to to fee the channel.")}
(: (IO (Try Any))
close)
(: (-> a (IO (Try Any)))
feed))
(def: (sink resolve)
(All [a]
(-> (async.Resolver (Maybe [a (Channel a)]))
(Sink a)))
(let [sink (atom.atom resolve)]
(implementation
(def: close
(loop [_ []]
(do {! io.monad}
[current (atom.read sink)
stopped? (current #.None)]
(if stopped?
## I closed the sink.
(in (exception.return []))
## Someone else interacted with the sink.
(do !
[latter (atom.read sink)]
(if (is? current latter)
## Someone else closed the sink.
(in (exception.except ..channel_is_already_closed []))
## Someone else fed the sink while I was closing it.
(recur [])))))))
(def: (feed value)
(loop [_ []]
(do {! io.monad}
[current (atom.read sink)
#let [[next resolve_next] (:sharing [a]
(async.Resolver (Maybe [a (Channel a)]))
current
[(Async (Maybe [a (Channel a)]))
(async.Resolver (Maybe [a (Channel a)]))]
(async.async []))]
fed? (current (#.Some [value next]))]
(if fed?
## I fed the sink.
(do !
[_ (atom.compare_and_swap current resolve_next sink)]
(in (exception.return [])))
## Someone else interacted with the sink.
(do !
[latter (atom.read sink)]
(if (is? current latter)
## Someone else closed the sink while I was feeding it.
(in (exception.except ..channel_is_already_closed []))
## Someone else fed the sink.
(recur []))))))))))
(def: #export (channel _)
{#.doc (doc "Creates a brand-new channel and hands it over, along with the sink to write to it.")}
(All [a] (-> Any [(Channel a) (Sink a)]))
(let [[async resolve] (async.async [])]
[async (..sink resolve)]))
(implementation: #export functor
(Functor Channel)
(def: (map f)
(async\map
(maybe\map
(function (_ [head tail])
[(f head) (map f tail)])))))
(implementation: #export apply
(Apply Channel)
(def: &functor ..functor)
(def: (apply ff fa)
(do async.monad
[item_f ff
item_a fa]
(case [item_f item_a]
[(#.Some [head_f tail_f]) (#.Some [head_a tail_a])]
(in (#.Some [(head_f head_a) (apply tail_f tail_a)]))
_
(in #.None)))))
(def: empty
Channel
(async.resolved #.None))
(implementation: #export monad
(Monad Channel)
(def: &functor ..functor)
(def: (in a)
(async.resolved (#.Some [a ..empty])))
(def: (join mma)
(let [[output sink] (channel [])]
(exec (: (Async Any)
(loop [mma mma]
(do {! async.monad}
[?mma mma]
(case ?mma
(#.Some [ma mma'])
(do !
[_ (loop [ma ma]
(do !
[?ma ma]
(case ?ma
(#.Some [a ma'])
(exec (io.run (\ sink feed a))
(recur ma'))
#.None
(in []))))]
(recur mma'))
#.None
(in (: Any (io.run (\ sink close))))))))
output))))
(type: #export (Subscriber a)
{#.doc (doc "A function that can receive every value fed into a channel.")}
(-> a (IO (Maybe Any))))
(def: #export (subscribe subscriber channel)
(All [a] (-> (Subscriber a) (Channel a) (IO Any)))
(io (exec (: (Async Any)
(loop [channel channel]
(do async.monad
[item channel]
(case item
(#.Some [head tail])
(case (io.run (subscriber head))
(#.Some _)
(recur tail)
#.None
(in []))
#.None
(in [])))))
[])))
(def: #export (only pass? channel)
{#.doc (doc "Produces a new channel based on the old one, only with values"
"that pass the test.")}
(All [a] (-> (-> a Bit) (Channel a) (Channel a)))
(do async.monad
[item channel]
(case item
(#.Some [head tail])
(let [tail' (only pass? tail)]
(if (pass? head)
(in (#.Some [head tail']))
tail'))
#.None
(in #.None))))
(def: #export (of_async async)
{#.doc (doc "A one-element channel containing the output from an async.")}
(All [a] (-> (Async a) (Channel a)))
(async\map (function (_ value)
(#.Some [value ..empty]))
async))
(def: #export (fold f init channel)
{#.doc "Asynchronous fold over channels."}
(All [a b]
(-> (-> b a (Async a)) a (Channel b)
(Async a)))
(do {! async.monad}
[item channel]
(case item
#.None
(in init)
(#.Some [head tail])
(do !
[init' (f head init)]
(fold f init' tail)))))
(def: #export (folds f init channel)
(All [a b]
(-> (-> b a (Async a)) a (Channel b)
(Channel a)))
(do {! async.monad}
[item channel]
(case item
#.None
(in (#.Some [init (in #.None)]))
(#.Some [head tail])
(do !
[init' (f head init)]
(in (#.Some [init (folds f init' tail)]))))))
(def: #export (poll milli_seconds action)
(All [a]
(-> Nat (IO a) [(Channel a) (Sink a)]))
(let [[output sink] (channel [])]
(exec (io.run (loop [_ []]
(do io.monad
[value action
_ (\ sink feed value)]
(async.await recur (async.wait milli_seconds)))))
[output sink])))
(def: #export (periodic milli_seconds)
(-> Nat [(Channel Any) (Sink Any)])
(..poll milli_seconds (io [])))
(def: #export (iterate f init)
(All [s o] (-> (-> s (Async (Maybe [s o]))) s (Channel o)))
(do async.monad
[?next (f init)]
(case ?next
(#.Some [state output])
(in (#.Some [output (iterate f state)]))
#.None
(in #.None))))
(def: (distinct' equivalence previous channel)
(All [a] (-> (Equivalence a) a (Channel a) (Channel a)))
(do async.monad
[item channel]
(case item
(#.Some [head tail])
(if (\ equivalence = previous head)
(distinct' equivalence previous tail)
(in (#.Some [head (distinct' equivalence head tail)])))
#.None
(in #.None))))
(def: #export (distinct equivalence channel)
(All [a] (-> (Equivalence a) (Channel a) (Channel a)))
(do async.monad
[item channel]
(case item
(#.Some [head tail])
(in (#.Some [head (distinct' equivalence head tail)]))
#.None
(in #.None))))
(def: #export (consume channel)
(All [a] (-> (Channel a) (Async (List a))))
(do {! async.monad}
[item channel]
(case item
(#.Some [head tail])
(\ ! map (|>> (#.Item head))
(consume tail))
#.None
(in #.End))))
(def: #export (sequential milli_seconds values)
{#.doc (doc "Transforms the given list into a channel with the same elements.")}
(All [a] (-> Nat (List a) (Channel a)))
(case values
#.End
..empty
(#.Item head tail)
(async.resolved (#.Some [head (do async.monad
[_ (async.wait milli_seconds)]
(sequential milli_seconds tail))]))))
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