From b47835644a16f43155b44333c0218293bcaf20a6 Mon Sep 17 00:00:00 2001
From: Eduardo Julian
Date: Sun, 9 Dec 2018 17:12:33 -0400
Subject: Basic implementation for sessions.

---
 lux-mode/lux-mode.el                         |   2 +-
 stdlib/source/lux/concurrency/session.lux    | 211 +++++++++++++++++++++++++++
 stdlib/source/lux/macro/syntax.lux           |  10 +-
 stdlib/test/test/lux/concurrency/session.lux |  78 ++++++++++
 4 files changed, 297 insertions(+), 4 deletions(-)
 create mode 100644 stdlib/source/lux/concurrency/session.lux
 create mode 100644 stdlib/test/test/lux/concurrency/session.lux

diff --git a/lux-mode/lux-mode.el b/lux-mode/lux-mode.el
index 45fbb75ec..1f2805a30 100644
--- a/lux-mode/lux-mode.el
+++ b/lux-mode/lux-mode.el
@@ -295,7 +295,7 @@ Called by `imenu--generic-function'."
                     function-application
                     ;;;;;;;;;;;;;;;;;;;;;;;;
                     "\\.module:"
-                    "def:" "type:" "program:" "context:"
+                    "def:" "type:" "program:" "context:" "choice:"
                     "macro:" "syntax:"
                     "with-expansions"
                     "exception:"
diff --git a/stdlib/source/lux/concurrency/session.lux b/stdlib/source/lux/concurrency/session.lux
new file mode 100644
index 000000000..9214860ca
--- /dev/null
+++ b/stdlib/source/lux/concurrency/session.lux
@@ -0,0 +1,211 @@
+(.module:
+  [lux #*
+   [control
+    ["." monad (#+ do)]
+    ["p" parser]]
+   [data
+    [text
+     format]
+    [collection
+     ["." list ("list/." Functor<List>)]]]
+   ["." io]
+   [type (#+ :share)]
+   ["." macro
+    ["." code]
+    ["s" syntax (#+ syntax:)
+     [common
+      ["." reader]
+      ["." writer]]]]]
+  [//
+   ["." promise (#+ Promise)]])
+
+(type: #export (Read value next)
+  {#.doc (doc "A reading step.")}
+  (Promise [value next]))
+
+(type: #export (Write value next)
+  {#.doc (doc "A writing step.")}
+  (-> value (Promise next)))
+
+(type: #export (Fork left right)
+  {#.doc (doc "A forking step, that allows choosing which path to take.")}
+  (All [next]
+    (-> (| (-> left next)
+           (-> right next))
+        (Promise next))))
+
+(type: #export (Join left right)
+  {#.doc (doc "A joining step, which communicates which path was taken.")}
+  (Promise (| left right)))
+
+(type: #export End
+  {#.doc (doc "Represents the end of a protocol.")}
+  [])
+
+(def: #export end
+  {#.doc (doc "The last step in a session.")}
+  [End End]
+  [[] []])
+
+(template: (!write <read> <write>)
+  (function (_ value)
+    (exec (io.run (promise.resolve [value <read>] channel))
+      (promise.promise (#.Some <write>)))))
+
+(def: #export receive
+  {#.doc (doc "A Read step for 'me', and a Write step for 'you'.")}
+  (All [value mine yours]
+    (-> [mine yours] [(Read value mine) (Write value yours)]))
+  (function (_ [mine yours])
+    (let [channel (promise.promise #.None)]
+      [channel
+       (!write mine yours)])))
+
+(def: #export send
+  {#.doc (doc "A Write step for 'me', and a Read step for 'you'.")}
+  (All [value mine yours]
+    (-> [mine yours] [(Write value mine) (Read value yours)]))
+  (function (_ [mine yours])
+    (let [channel (promise.promise #.None)]
+      [(!write yours mine)
+       channel])))
+
+(def: #export (fork left right)
+  {#.doc (doc "A Fork step for 'me', and a Join step for 'you'.")}
+  (All [myL yourL myR yourR]
+    (-> [myL yourL] [myR yourR]
+        [(Fork myL myR) (Join yourL yourR)]))
+  (let [[myL yourL] left
+        [myR yourR] right
+        channel (:share [yourL yourR]
+                        {[yourL yourR]
+                         [yourL yourR]}
+                        {(Join yourL yourR)
+                         (promise.promise #.None)})]
+    [(function (_ signal)
+       (case signal
+         (#.Left go)
+         (exec (io.run (promise.resolve (#.Left yourL) channel))
+           (promise.promise (#.Some (go myL))))
+         
+         (#.Right go)
+         (exec (io.run (promise.resolve (#.Right yourR) channel))
+           (promise.promise (#.Some (go myR))))))
+     channel]))
+
+(def: #export (join left right)
+  {#.doc (doc "A Join step for 'me', and a Fork step for 'you'.")}
+  (All [myL yourL myR yourR]
+    (-> [myL yourL] [myR yourR]
+        [(Join myL myR) (Fork yourL yourR)]))
+  (let [[myL yourL] left
+        [myR yourR] right
+        channel (:share [myL myR]
+                        {[myL myR]
+                         [myL myR]}
+                        {(Join myL myR)
+                         (promise.promise #.None)})]
+    [channel
+     (function (_ signal)
+       (case signal
+         (#.Left go)
+         (exec (io.run (promise.resolve (#.Left myL) channel))
+           (promise.promise (#.Some (go yourL))))
+         
+         (#.Right go)
+         (exec (io.run (promise.resolve (#.Right myR) channel))
+           (promise.promise (#.Some (go yourR))))))]))
+
+(do-template [<name> <side> <doc>]
+  [(def: #export (<name> session)
+     {#.doc (doc <doc>)}
+     (All [mine yours] (-> [mine yours] <side>))
+     (let [[mine yours] session]
+       <side>))]
+
+  [my   mine
+   "'My' side of the session."]
+  [your yours
+   "'Your' side of the session."]
+  )
+
+(type: #export Session
+  {#.doc (doc "A pair of types, for 'me' and 'you'."
+              "They describe each side in a session protocol.")}
+  [Type Type])
+
+(def: counterpart-doc
+  (-> Name Code)
+  (|>> %name (format "The session/type counterpart to ") code.text))
+
+(do-template [<name> <alias> <me> <you> <counterpart>]
+  [(def: #export (<name> value [mine yours])
+     {#.doc (doc (counterpart-doc (name-of <counterpart>)))}
+     (-> Type Session Session)
+     [(type (<me> value mine)) (type (<you> value yours))])
+
+   (def: #export <alias>
+     {#.doc (doc <doc>)}
+     <name>)]
+
+  [$receive ?? Read  Write ..receive]
+  [$send    !! Write Read  ..send]
+  )
+
+(def: #export $end
+  {#.doc (doc (counterpart-doc (name-of ..end)))}
+  Session
+  [End End])
+
+(def: #export >>
+  {#.doc (doc (counterpart-doc (name-of ..end)))}
+  $end)
+
+(do-template [<name> <alias> <+> <-> <counterpart>]
+  [(def: #export (<name> [myL yourL] [myR yourR])
+     {#.doc (doc (counterpart-doc (name-of <counterpart>)))}
+     (-> Session Session Session)
+     [(type (<+> myL myR)) (type (<-> yourL yourR))])
+
+   (def: #export <alias>
+     {#.doc (doc (counterpart-doc (name-of <counterpart>)))}
+     <name>)]
+
+  [$join /\ Join Fork ..join]
+  [$fork \/ Fork Join ..fork]
+  )
+
+(def: #export ($session [mine yours])
+  {#.doc (doc "Create an actual type from a session.")}
+  (-> Session Type)
+  (type [mine yours]))
+
+(def: #export <<
+  {#.doc (doc "Create an actual type from a session.")}
+  $session)
+
+(do-template [<name> <alias> <side> <counterpart>]
+  [(def: #export (<name> [mine yours])
+     {#.doc (doc (counterpart-doc (name-of <counterpart>)))}
+     (-> Session Type)
+     <side>)
+
+   (def: #export <alias> <name>)]
+
+  [$my   +<< mine  ..my]
+  [$your -<< yours ..your]
+  )
+
+(syntax: #export (choice: {export reader.export}
+                   {name s.local-identifier}
+                   {tags (s.tuple (p.many s.local-tag))})
+  {#.doc (doc "Defines tags to be used for fork/join branching in sessions.")}
+  (do @
+    [g!vars (monad.map @ macro.gensym
+                       (list.repeat (list.size tags) "var"))
+     #let [cases (list/map (function (_ [tag g!var])
+                             (` ((~ (code.local-tag tag)) (~ g!var))))
+                           (list.zip2 tags g!vars))]]
+    (wrap (list (` (type: (~+ (writer.export export)) ((~ (code.local-identifier name))
+                                                       (~+ g!vars))
+                     (~+ cases)))))))
diff --git a/stdlib/source/lux/macro/syntax.lux b/stdlib/source/lux/macro/syntax.lux
index 07b0a4b9e..edee25af3 100644
--- a/stdlib/source/lux/macro/syntax.lux
+++ b/stdlib/source/lux/macro/syntax.lux
@@ -107,7 +107,7 @@
          (#error.Error ($_ text/compose "Cannot parse local " <desc> (remaining-inputs tokens))))))]
 
   [local-identifier #.Identifier "identifier"]
-  [   local-tag #.Tag    "tag"]
+  [   local-tag     #.Tag        "tag"]
   )
 
 (do-template [<name> <tag> <desc>]
@@ -195,6 +195,10 @@
       (wrap [real value]))))
 
 ## [Syntax]
+(def: (quote name)
+  (-> Text Text)
+  ($_ text/compose "'" name "'"))
+
 (macro: #export (syntax: tokens)
   {#.doc (doc "A more advanced way to define macros than 'macro:'."
               "The inputs to the macro can be parsed in complex ways through the use of syntax parsers."
@@ -250,7 +254,7 @@
                                           (//.fail "Syntax pattern expects records or identifiers."))))
                                    args)
            #let [g!state (code.identifier ["" "*compiler*"])
-                 error-msg (code.text (text/compose "Wrong syntax for " name))
+                 error-msg (code.text ($_ text/compose "Wrong syntax for " (quote name) ": "))
                  export-ast (: (List Code)
                                (if exported?
                                  (list (' #export))
@@ -271,4 +275,4 @@
                                              (~ body)))))))))))))
       
       _
-      (//.fail "Wrong syntax for syntax:"))))
+      (//.fail (text/compose "Wrong syntax for " (quote "syntax:"))))))
diff --git a/stdlib/test/test/lux/concurrency/session.lux b/stdlib/test/test/lux/concurrency/session.lux
new file mode 100644
index 000000000..ad0343d15
--- /dev/null
+++ b/stdlib/test/test/lux/concurrency/session.lux
@@ -0,0 +1,78 @@
+(.module:
+  [lux #*
+   [control
+    [monad (#+ do)]]
+   [concurrency
+    ["." promise]
+    ["$" session (#+ Session choice: << >> ?? !! +<< -<< \/ /\)]]
+   [data
+    [text
+     format]]
+   [math
+    ["r" random]]]
+  lux/test)
+
+(choice: Calculation [#Add #Negate])
+
+(def: $add (<| (!! Int) (!! Int) (?? Int) >>))
+(def: $negate (<| (!! Int) (?? Int) >>))
+
+(def: (add-session _)
+  (-> [] (:~ (<< $add)))
+  (<| $.send $.send $.receive $.end))
+
+(def: (negate-session _)
+  (-> [] (:~ (<< $negate)))
+  (<| $.send $.receive $.end))
+
+(def: $calculation
+  Session
+  ($_ \/
+      $add
+      $negate))
+
+(def: (calculation-session _)
+  (-> [] (:~ (<< $calculation)))
+  ($_ $.fork
+      (add-session [])
+      (negate-session [])))
+
+(def: (__my-calculation _)
+  (-> [] (:~ (+<< $calculation)))
+  ($.my (calculation-session [])))
+
+(def: (__your-calculation _)
+  (-> [] (:~ (-<< $calculation)))
+  ($.your (calculation-session [])))
+
+(context: "Sessions."
+  (do @
+    [#let [[$me $you] (calculation-session [])]
+     param r.int
+     subject r.int]
+    ($_ seq
+        (wrap (do promise.Monad<Promise>
+                [$me ($me (#Add id))
+                 $me ($me param)
+                 $me ($me subject)
+                 [output $end] $me]
+                (assert "Client [#Add]"
+                        (i/= (i/+ param subject) output))))
+        (wrap (do promise.Monad<Promise>
+                [choice $you]
+                (case choice
+                  (#Add $you)
+                  (do @
+                    [[param-input $you] $you
+                     [subject-input $you] $you
+                     $end ($you (i/+ param-input subject-input))]
+                    (assert "Server [#Add]"
+                            true))
+                  
+                  (#Negate $you)
+                  (do @
+                    [[subject $you] $you
+                     $end ($you (i/* -1 subject))]
+                    (assert "Server [#Negate]"
+                            true)))))
+        )))
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