syndicate-2017/js/compiler/demo-santa.js

// bin/syndicatec compiler/demo-santa.js | node
//
// Santa Claus Problem
// https://www.schoolofhaskell.com/school/advanced-haskell/beautiful-concurrency/4-the-santa-claus-problem
// https://arxiv.org/pdf/1810.09613.pdf

var Immutable = require('immutable');
var Syndicate = require('./src/main.js');

assertion type elfProblem(id);
assertion type reindeerReturned(id);

assertion type problemResolved(id);
assertion type deliverToys();

function sleep(milliseconds, continuation) {
  react {
    var deadline = +(new Date()) + milliseconds;
    stop on asserted Syndicate.Timer.timeLaterThan(deadline) {
      continuation();
    }
  }
}

var elfCount = 0;
function elf() {
  var elfId = "elf" + ++elfCount;
  spawn* named elfId {
    function workIndustriously() {
      console.log(elfId, "is working.");
      sleep(Math.random() * 1000.0, haveAProblem);
    }

    function haveAProblem() {
      console.log(elfId, "has a problem!");
      react {
        assert elfProblem(elfId);
        stop on asserted problemResolved(elfId) {
          console.log(elfId, "'s problem is resolved.");
          workIndustriously();
        }
      }
    }

    workIndustriously();
  }
}

var reindeerCount = 0;
function reindeer() {
  var reindeerId = "reindeer" + ++reindeerCount;
  spawn* named reindeerId {
    function holiday() {
      console.log(reindeerId, "is on holiday.");
      sleep(Math.random() * 9000.0, returnToWork);
    }

    function returnToWork() {
      console.log(reindeerId, "has returned from holiday and is ready to deliver toys!");
      react {
        assert reindeerReturned(reindeerId);
        stop on asserted deliverToys() {
          console.log(reindeerId, "delivers toys with the other reindeer.");
          react {
            stop on retracted deliverToys() {
              console.log(reindeerId, "has been dismissed by Santa.");
              holiday();
            }
          }
        }
      }
    }

    holiday();
  }
}

ground dataspace {
  Syndicate.Timer.spawnTimerDriver();

  var nElves = 10;
  var elfGroupSize = 3;
  var nReindeer = 9;

  for (var i = 0; i < nElves; i++) { elf(); }
  for (var i = 0; i < nReindeer; i++) { reindeer(); }

  spawn* named "Santa" {
    function waitForWork() {
      console.log("Santa is waiting for something to do.");
      react {
        field this.puzzledElves = Immutable.List();
        on asserted elfProblem($id) { this.puzzledElves = this.puzzledElves.push(id); }
        stop on (this.puzzledElves.size >= elfGroupSize) {
          talkToElves(this.puzzledElves.take(elfGroupSize));
        }

        field this.readyReindeer = Immutable.List();
        on asserted reindeerReturned($id) { this.readyReindeer = this.readyReindeer.push(id); }
        stop on (this.readyReindeer.size == nReindeer) {
          harnessReindeer();
        }
      }
    }

    function talkToElves(elves) {
      if (elves.isEmpty()) {
        waitForWork();
      } else {
        var elf = elves.first();
        console.log("Santa resolves the problem of", elf);
        react {
          assert problemResolved(elf);
          stop on retracted elfProblem(elf) {
            talkToElves(elves.shift());
          }
        }
      }
    }

    function harnessReindeer() {
      console.log("Santa does the delivery run!");
      react {
        assert deliverToys();
        stop on retracted reindeerReturned(_) {
          waitForWork();
        }
      }
    }

    waitForWork()
  }
}