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(;module: {#;doc "The actor model of concurrency."}
lux
(lux (control monad)
[io #- run]
(codata function)
(data [error #- fail]
text/format
(coll [list "List/" Monoid<List> Monad<List>])
[product]
[number "Nat/" Codec<Text,Nat>])
[compiler #+ with-gensyms]
(macro [ast]
["s" syntax #+ syntax: Syntax]
(syntax [common]))
[type])
(.. ["P" promise #+ Monad<Promise>]
[stm #+ Monad<STM>]
[frp]))
## [Types]
(type: #export (Actor s m)
{#;doc "An actor, defined as all the necessities it requires."}
{#mailbox (stm;Var m)
#kill-signal (P;Promise Unit)
#obituary (P;Promise [(Maybe Text) s (List m)])})
(type: #export (Behavior s m)
{#;doc "An actor's behavior when messages are received."}
{#step (-> (Actor s m) (-> m s (P;Promise (Error s))))
#end (-> (Maybe Text) s (P;Promise Unit))})
## [Values]
(def: #export (spawn init behavior)
{#;doc "Given a behavior and initial state, spawns an actor and returns it."}
(All [s m] (-> s (Behavior s m) (IO (Actor s m))))
(io (let [[step on-death] behavior
mailbox (stm;var (:! ($ +1) []))
kill-signal (P;promise Unit)
obituary (P;promise [(Maybe Text) ($ +0) (List ($ +1))])
self {#mailbox mailbox
#kill-signal kill-signal
#obituary obituary}
mailbox-chan (io;run (stm;follow "\tmailbox\t" mailbox))
step (step self)
|mailbox| (stm;var mailbox-chan)
_ (:: Monad<Promise> map
(lambda [_]
(io;run (do Monad<IO>
[mb (stm;read! |mailbox|)]
(frp;close mb))))
kill-signal)
process (loop [state init
messages mailbox-chan]
(do Monad<Promise>
[?messages+ messages]
(case ?messages+
## No kill-signal so far, so I may proceed...
(#;Some [message messages'])
(do Monad<Promise>
[#let [_ (io;run (stm;write! messages' |mailbox|))]
?state' (step message state)]
(case ?state'
(#;Left error)
(do @
[#let [_ (io;run (P;resolve [] kill-signal))
_ (io;run (frp;close messages'))
death-message (#;Some error)]
_ (on-death death-message state)
remaining-messages (frp;consume messages')]
(wrap [death-message state (#;Cons message remaining-messages)]))
(#;Right state')
(recur state' messages')))
## Otherwise, clean-up and return current state.
#;None
(do Monad<Promise>
[#let [_ (io;run (frp;close messages))
death-message #;None]
_ (on-death death-message state)]
(wrap [death-message state (list)])))))]
self)))
(def: #export poison
{#;doc "Immediately kills the given actor (if it's not already dead)."}
(All [s m] (-> (Actor s m) (io;IO Bool)))
(|>. (get@ #kill-signal) (P;resolve [])))
(def: #export (alive? actor)
(All [s m] (-> (Actor s m) Bool))
(case [(P;poll (get@ #kill-signal actor))
(P;poll (get@ #obituary actor))]
[#;None #;None]
true
_
false))
(def: #export (send message actor)
{#;doc "Communicate with an actor through message passing."}
(All [s m] (-> m (Actor s m) (P;Promise Bool)))
(if (alive? actor)
(exec (io;run (stm;write! message (get@ #mailbox actor)))
(:: Monad<Promise> wrap true))
(:: Monad<Promise> wrap false)))
(def: #export (keep-alive init behavior)
{#;doc "Given initial-state and a behavior, spawns an actor that will reboot if it dies of errors.
However, if it is killed, it won't re-spawn."}
(All [s m] (-> s (Behavior s m) (IO (Actor s m))))
(io (let [ka-actor (: (Actor (Actor ($ +0) ($ +1)) ($ +1))
(io;run (spawn (io;run (spawn init behavior))
{#step (lambda [*self* message server]
(do Monad<Promise>
[was-sent? (send message server)]
(if was-sent?
(wrap (#;Right server))
(do @
[[?cause state unprocessed-messages] (get@ #obituary server)]
(exec (log! (format "ACTOR DIED:" "\n"
(default "" ?cause) "\n"
"RESTARTING" "\n"))
(do @
[#let [new-server (io;run (spawn state behavior))
mailbox (get@ #mailbox new-server)]
_ (P;future (mapM io;Monad<IO> ((flip stm;write!) mailbox) (#;Cons message unprocessed-messages)))]
(wrap (#;Right new-server))))
))))
#end (lambda [_ server] (exec (io;run (poison server))
(:: Monad<Promise> wrap [])))})))]
(update@ #obituary (: (-> (P;Promise [(Maybe Text) (Actor ($ +0) ($ +1)) (List ($ +1))])
(P;Promise [(Maybe Text) ($ +0) (List ($ +1))]))
(lambda [process]
(do Monad<Promise>
[[_ server unprocessed-messages-0] process
[cause state unprocessed-messages-1] (get@ #obituary server)]
(wrap [cause state (List/append unprocessed-messages-0 unprocessed-messages-1)]))))
ka-actor))))
## [Syntax]
(type: Method
{#name Text
#vars (List Text)
#args (List [Text AST])
#return AST
#body AST})
(def: method^
(Syntax Method)
(s;form (do s;Monad<Syntax>
[_ (s;this! (' method:))
vars (s;default (list) (s;tuple (s;some s;local-symbol)))
[name args] (s;form ($_ s;seq
s;local-symbol
(s;many common;typed-arg)
))
return s;any
body s;any]
(wrap {#name name
#vars vars
#args args
#return return
#body body}))))
(def: stop^
(Syntax AST)
(s;form (do s;Monad<Syntax>
[_ (s;this! (' stop:))]
s;any)))
(def: actor-decl^
(Syntax [(List Text) Text (List [Text AST])])
(s;seq (s;default (list) (s;tuple (s;some s;local-symbol)))
(s;either (s;form (s;seq s;local-symbol (s;many common;typed-arg)))
(s;seq s;local-symbol (:: s;Monad<Syntax> wrap (list))))))
(def: (actor-def-decl [_vars _name _args] return-type)
(-> [(List Text) Text (List [Text AST])] AST (List AST))
(let [decl (` ((~ (ast;symbol ["" (format _name "//new")])) (~@ (List/map (|>. product;left [""] ast;symbol) _args))))
base-type (` (-> (~@ (List/map product;right _args))
(~ return-type)))
type (case _vars
#;Nil
base-type
_
(` (All [(~@ (List/map (|>. [""] ast;symbol) _vars))]
(~ base-type))))]
(list decl
type)))
(syntax: #export (actor: [_ex-lev common;export-level]
[(^@ decl [_vars _name _args]) actor-decl^]
state-type
[methods (s;many method^)]
[?stop (s;opt stop^)])
{#;doc (doc "Allows defining an actor, with a pice of state and a set of methods that can be called on it."
"A method can access the actor's state through the *state* variable."
"A method can also access the actor itself through the *self* variable."
"A method may succeed or fail (in case of failure, the actor dies). This is handled through the Either type."
"A method's output must be a promise containing a 2-tuple with the updated state and a return value."
"All methods are run implicitly within the Promise monad."
(actor: #export Adder
Int
(method: (count! [to-add Int])
[Int Int]
(if (i.>= 0 to-add)
(let [new-state (i.+ to-add *state*)]
(wrap (#;Right [new-state [*state* new-state]])))
(wrap (#;Left "Can't add negative numbers!"))))
))}
(with-gensyms [g!message g!error g!return g!error g!output]
(let [g!state-name (ast;symbol ["" (format _name "//STATE")])
g!protocol-name (ast;symbol ["" (format _name "//PROTOCOL")])
g!self (ast;symbol ["" "*self*"])
g!state (ast;symbol ["" "*state*"])
g!cause (ast;symbol ["" "*cause*"])
g!stop-body (default (` (:: P;Monad<Promise> (~' wrap) [])) ?stop)
protocol (List/map (lambda [(^slots [#name #vars #args #return #body])]
(` ((~ (ast;tag ["" name])) [(~@ (List/map product;right args))] (P;Promise (~ return)))))
methods)
protocol-pm (List/map (: (-> Method [AST AST])
(lambda [(^slots [#name #vars #args #return #body])]
(let [arg-names (|> (list;size args) (list;n.range +1) (List/map (|>. Nat/encode [""] ast;symbol)))
body-func (` (: (-> (~ g!state-name) (~@ (List/map product;right args)) (P;Promise (Error [(~ g!state-name) (~ return)])))
(lambda (~ (ast;symbol ["" _name])) [(~ g!state) (~@ (List/map (|>. product;left [""] ast;symbol) args))]
(do P;Monad<Promise>
[]
(~ body)))))]
[(` [[(~@ arg-names)] (~ g!return)])
(` (do P;Monad<Promise>
[(~ g!output) ((~ body-func) (~ g!state) (~@ arg-names))]
(case (~ g!output)
(#;Right [(~ g!state) (~ g!output)])
(exec (io;run (P;resolve (~ g!output) (~ g!return)))
((~' wrap) (#;Right (~ g!state))))
(#;Left (~ g!error))
((~' wrap) (#;Left (~ g!error))))
))])))
methods)
g!behavior (` {#step (lambda [(~ g!self) (~ g!message) (~ g!state)]
(case (~ g!message)
(~@ (if (n.= +1 (list;size protocol-pm))
(List/join (List/map (lambda [[pattern clause]]
(list pattern clause))
protocol-pm))
(List/join (List/map (lambda [[method [pattern clause]]]
(list (` ((~ (ast;tag ["" (get@ #name method)])) (~ pattern)))
clause))
(list;zip2 methods protocol-pm)))))
))
#end (lambda [(~ g!cause) (~ g!state)]
(do P;Monad<Promise>
[]
(~ g!stop-body)))})
g!actor-name (ast;symbol ["" _name])
g!methods (List/map (: (-> Method AST)
(lambda [(^slots [#name #vars #args #return #body])]
(let [arg-names (|> (list;size args) (list;n.range +1) (List/map (|>. Nat/encode [""] ast;symbol)))
type (` (-> (~@ (List/map product;right args))
(~ g!actor-name)
(P;Promise (~ return))))]
(` (def: (~@ (common;gen-export-level _ex-lev)) ((~ (ast;symbol ["" name])) (~@ arg-names) (~ g!self))
(~ type)
(let [(~ g!output) (P;promise (~ return))]
(exec (send ((~ (ast;tag ["" name])) [[(~@ arg-names)] (~ g!output)]) (~ g!self))
(~ g!output))))))))
methods)]
(wrap (list& (` (type: (~@ (common;gen-export-level _ex-lev)) (~ g!state-name) (~ state-type)))
(` (type: (~@ (common;gen-export-level _ex-lev)) (~ g!protocol-name) (~@ protocol)))
(` (type: (~@ (common;gen-export-level _ex-lev)) (~ g!actor-name) (Actor (~ g!state-name) (~ g!protocol-name))))
(` (def: (~@ (common;gen-export-level _ex-lev)) (~@ (actor-def-decl decl (` (Behavior (~ g!state-name) (~ g!protocol-name)))))
(~ g!behavior)))
g!methods))
)))
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