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## Copyright (c) Eduardo Julian. All rights reserved.
## This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
## If a copy of the MPL was not distributed with this file,
## You can obtain one at http://mozilla.org/MPL/2.0/.
(;module:
lux
(lux (control functor
applicative
monad
eq)
(codata [io #- run]
function)
(data (struct [list])
text/format)
[compiler]
(macro ["s" syntax #+ syntax: Syntax]))
(.. ["&" promise]))
## [Types]
(type: #export (Chan a)
{#;doc "An asynchronous channel of values which may be closed.
Reading from a channel does not remove the read piece of data, as it can still be accessed if you have an earlier node of the channel."}
(&;Promise (Maybe [a (Chan a)])))
## [Syntax]
(syntax: #export (chan [?type (s;opt s;any)])
{#;doc (doc "Makes an uninitialized Chan (in this case, of Unit)."
(chan Unit)
"The type is optional."
(chan))}
(case ?type
(#;Some type)
(wrap (list (` (: (Chan (~ type))
(&;promise)))))
#;None
(wrap (list (` (&;promise))))))
## [Values]
(def: #export (filter p xs)
(All [a] (-> (-> a Bool) (Chan a) (Chan a)))
(do &;Monad<Promise>
[?x+xs xs]
(case ?x+xs
#;None (wrap #;None)
(#;Some [x xs']) (if (p x)
(wrap (#;Some [x (filter p xs')]))
(filter p xs')))))
(def: #export (write value chan)
{#;doc "Write to a channel, so long as it's still open."}
(All [a] (-> a (Chan a) (IO (Maybe (Chan a)))))
(case (&;poll chan)
(^template [<case> <chan-to-write>]
<case>
(do Monad<IO>
[#let [new-tail (&;promise)]
done? (&;resolve (#;Some [value new-tail]) <chan-to-write>)]
(if done?
(wrap (#;Some new-tail))
(write value <chan-to-write>))))
([#;None chan]
[(#;Some (#;Some [_ chan'])) chan'])
_
(:: Monad<IO> wrap #;None)
))
(def: #export (close chan)
(All [a] (-> (Chan a) (IO Bool)))
(case (&;poll chan)
(^template [<case> <chan-to-write>]
<case>
(do Monad<IO>
[done? (&;resolve #;None <chan-to-write>)]
(if done?
(wrap true)
(close <chan-to-write>))))
([#;None chan]
[(#;Some (#;Some [_ chan'])) chan'])
_
(:: Monad<IO> wrap false)
))
(def: (pipe' input output)
(All [a] (-> (Chan a) (Chan a) (&;Promise Unit)))
(do &;Monad<Promise>
[?x+xs input]
(case ?x+xs
#;None (wrap [])
(#;Some [x input']) (case (io;run (write x output))
#;None
(wrap [])
(#;Some output')
(pipe' input' output')))))
(def: #export (pipe input output)
{#;doc "Copy/pipe the contents of a channel on to another."}
(All [a] (-> (Chan a) (Chan a) (&;Promise Unit)))
(do &;Monad<Promise>
[_ (pipe' input output)]
(exec (io;run (close output))
(wrap []))))
(def: #export (merge xss)
{#;doc "Fuse all the elements in a list of channels by piping them onto a new output channel."}
(All [a] (-> (List (Chan a)) (Chan a)))
(let [output (chan ($ +0))]
(exec (do &;Monad<Promise>
[_ (mapM @ (lambda [input] (pipe' input output)) xss)]
(exec (io;run (close output))
(wrap [])))
output)))
(def: #export (fold f init xs)
{#;doc "Asynchronous fold over channels."}
(All [a b] (-> (-> b a (&;Promise a)) a (Chan b) (&;Promise a)))
(do &;Monad<Promise>
[?x+xs xs]
(case ?x+xs
#;None (wrap init)
(#;Some [x xs']) (do @
[init' (f x init)]
(fold f init' xs')))))
(def: (no-dups' eq last-one xs)
(All [a] (-> (Eq a) a (Chan a) (Chan a)))
(let [(^open) eq]
(do &;Monad<Promise>
[?x+xs xs]
(case ?x+xs
#;None (wrap #;None)
(#;Some [x xs']) (if (= x last-one)
(no-dups' eq last-one xs')
(wrap (#;Some [x (no-dups' eq x xs')])))))))
(def: #export (no-dups eq xs)
{#;doc "Multiple consecutive equal values in the input channel will just be single value in the output channel."}
(All [a] (-> (Eq a) (Chan a) (Chan a)))
(let [(^open) eq]
(do &;Monad<Promise>
[?x+xs xs]
(case ?x+xs
#;None (wrap #;None)
(#;Some [x xs']) (wrap (#;Some [x (no-dups' eq x xs')]))))))
(def: #export (consume xs)
{#;doc "Reads the entirety of a channel's contents and returns them as a list."}
(All [a] (-> (Chan a) (&;Promise (List a))))
(do &;Monad<Promise>
[?x+xs' xs]
(case ?x+xs'
#;None
(wrap #;Nil)
(#;Some [x xs'])
(do @
[=xs (consume xs')]
(wrap (#;Cons x =xs))))))
(def: #export (as-chan p)
(All [a] (-> (&;Promise a) (Chan a)))
(do &;Monad<Promise>
[x p]
(wrap (#;Some [x (wrap #;None)]))))
## [Structures]
(struct: #export _ (Functor Chan)
(def: (map f xs)
(:: &;Functor<Promise> map
(lambda [?x+xs]
(case ?x+xs
#;None #;None
(#;Some [x xs']) (#;Some [(f x) (map f xs')])))
xs)))
(struct: #export _ (Applicative Chan)
(def: functor Functor<Chan>)
(def: (wrap a)
(let [(^open) &;Monad<Promise>]
(wrap (#;Some [a (wrap #;None)]))))
(def: (apply ff fa)
(let [fb (chan ($ +1))]
(exec (let [(^open) Functor<Chan>]
(map (lambda [f] (pipe (map f fa) fb))
ff))
fb))))
(struct: #export _ (Monad Chan)
(def: applicative Applicative<Chan>)
(def: (join mma)
(let [output (chan ($ +0))]
(exec (let [(^open) Functor<Chan>]
(map (lambda [ma]
(pipe ma output))
mma))
output))))
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