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(.module:
[lux #*
[abstract
[predicate (#+ Predicate)]
[equivalence (#+ Equivalence)]
[functor (#+ Functor)]
[apply (#+ Apply)]
["." monad (#+ Monad do)]]
[control
["." try (#+ Try)]
["ex" exception (#+ exception:)]
["." io (#+ IO io)]]
[data
["." maybe ("#@." functor)]
[collection
["." list ("#@." monoid)]]]
[type (#+ :share)
abstract]]
[//
["." atom (#+ Atom)]
["." promise (#+ Promise) ("#@." functor)]])
(type: #export (Channel a)
{#.doc "An asynchronous channel to distribute values."}
(Promise (Maybe [a (Channel a)])))
(exception: #export channel-is-already-closed)
(signature: #export (Sink a)
(: (IO (Try Any))
close)
(: (-> a (IO (Try Any)))
feed))
(def: (sink resolve)
(All [a]
(-> (promise.Resolver (Maybe [a (Channel a)]))
(Sink a)))
(let [sink (atom.atom resolve)]
(structure
(def: close
(loop [_ []]
(do io.monad
[current (atom.read sink)
stopped? (current #.None)]
(if stopped?
## I closed the sink.
(wrap (ex.return []))
## Someone else interacted with the sink.
(do @
[latter (atom.read sink)]
(if (is? current latter)
## Someone else closed the sink.
(wrap (ex.throw 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] (:share [a]
{(promise.Resolver (Maybe [a (Channel a)]))
current}
{[(Promise (Maybe [a (Channel a)]))
(promise.Resolver (Maybe [a (Channel a)]))]
(promise.promise [])})]
fed? (current (#.Some [value next]))]
(if fed?
## I fed the sink.
(do @
[_ (atom.compare-and-swap current resolve-next sink)]
(wrap (ex.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.
(wrap (ex.throw channel-is-already-closed []))
## Someone else fed the sink.
(recur []))))))))))
(def: #export (channel _)
(All [a] (-> Any [(Channel a) (Sink a)]))
(let [[promise resolve] (promise.promise [])]
[promise (..sink resolve)]))
(structure: #export functor (Functor Channel)
(def: (map f)
(promise@map
(maybe@map
(function (_ [head tail])
[(f head) (map f tail)])))))
(structure: #export apply (Apply Channel)
(def: &functor ..functor)
(def: (apply ff fa)
(do promise.monad
[cons-f ff
cons-a fa]
(case [cons-f cons-a]
[(#.Some [head-f tail-f]) (#.Some [head-a tail-a])]
(wrap (#.Some [(head-f head-a) (apply tail-f tail-a)]))
_
(wrap #.None)))))
(def: empty Channel (promise.resolved #.None))
(structure: #export monad (Monad Channel)
(def: &functor ..functor)
(def: (wrap a)
(promise.resolved (#.Some [a ..empty])))
(def: (join mma)
(let [[output sink] (channel [])]
(exec (: (Promise Any)
(loop [mma mma]
(do promise.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
(wrap []))))]
(recur mma'))
#.None
(wrap (: Any (io.run (:: sink close))))))))
output))))
(def: #export (listen listener channel)
(All [a] (-> (-> a (IO Any)) (Channel a) (IO Any)))
(io (exec (: (Promise Any)
(loop [channel channel]
(do promise.monad
[cons channel]
(case cons
(#.Some [head tail])
(exec (io.run (listener head))
(recur tail))
#.None
(wrap [])))))
[])))
(def: #export (filter pass? channel)
(All [a] (-> (Predicate a) (Channel a) (Channel a)))
(do promise.monad
[cons channel]
(case cons
(#.Some [head tail])
(let [tail' (filter pass? tail)]
(if (pass? head)
(wrap (#.Some [head tail']))
tail'))
#.None
(wrap #.None))))
(def: #export (from-promise promise)
(All [a] (-> (Promise a) (Channel a)))
(promise@map (function (_ value)
(#.Some [value ..empty]))
promise))
(def: #export (fold f init channel)
{#.doc "Asynchronous fold over channels."}
(All [a b]
(-> (-> b a (Promise a)) a (Channel b)
(Promise a)))
(do promise.monad
[cons channel]
(case cons
#.None
(wrap init)
(#.Some [head tail])
(do @
[init' (f head init)]
(fold f init' tail)))))
(def: #export (folds f init channel)
{#.doc "A channel of folds."}
(All [a b]
(-> (-> b a (Promise a)) a (Channel b)
(Channel a)))
(do promise.monad
[cons channel]
(case cons
#.None
(wrap (#.Some [init (wrap #.None)]))
(#.Some [head tail])
(do @
[init' (f head init)]
(folds f init' tail)))))
(def: #export (poll milli-seconds action)
(All [a] (-> Nat (IO a) (Channel a)))
(let [[output sink] (channel [])]
(exec (io.run (loop [_ []]
(do io.monad
[value action
_ (:: sink feed value)]
(promise.await recur (promise.wait milli-seconds)))))
output)))
(def: #export (periodic milli-seconds)
(-> Nat (Channel Any))
(poll milli-seconds (io [])))
(def: #export (iterate f init)
(All [a] (-> (-> a (Promise (Maybe a))) a (Channel a)))
(do promise.monad
[?next (f init)]
(case ?next
(#.Some next)
(wrap (#.Some [init (iterate f next)]))
#.None
(wrap (#.Some [init (wrap #.None)])))))
(def: (distinct' equivalence previous channel)
(All [a] (-> (Equivalence a) a (Channel a) (Channel a)))
(do promise.monad
[cons channel]
(case cons
(#.Some [head tail])
(if (:: equivalence = previous head)
(distinct' equivalence previous tail)
(wrap (#.Some [head (distinct' equivalence head tail)])))
#.None
(wrap #.None))))
(def: #export (distinct equivalence channel)
(All [a] (-> (Equivalence a) (Channel a) (Channel a)))
(do promise.monad
[cons channel]
(case cons
(#.Some [head tail])
(wrap (#.Some [head (distinct' equivalence head tail)]))
#.None
(wrap #.None))))
(def: #export (consume channel)
{#.doc "Reads the entirety of a channel's content and returns it as a list."}
(All [a] (-> (Channel a) (Promise (List a))))
(do promise.monad
[cons channel]
(case cons
(#.Some [head tail])
(:: @ map (|>> (#.Cons head))
(consume tail))
#.None
(wrap #.Nil))))
(def: #export (sequential milli-seconds values)
(All [a] (-> Nat (List a) (Channel a)))
(case values
#.Nil
..empty
(#.Cons head tail)
(promise.resolved (#.Some [head (do promise.monad
[_ (promise.wait milli-seconds)]
(sequential milli-seconds tail))]))))
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