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New example - this one for the command line!

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Tony Garnock-Jones 2016-07-11 12:04:10 -04:00
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js/examples/two-buyer-protocol/.gitignore vendored Normal file
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index.expanded.js
index.md

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js/examples/two-buyer-protocol/Makefile Normal file
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TARGETS=index.expanded.js index.md
all: $(TARGETS)
%.expanded.js: %.js
../../bin/syndicatec $< > $@ || (rm -f $@; false)
%.md: %.js
sed -E -e 's:^: :g' -e 's:^ /// ?::g' -e 's:^ $$::g' < $< > $@
clean:
rm -f $(TARGETS)

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js/examples/two-buyer-protocol/index.js Normal file
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/// ---
/// title: Two-Party Buyer Protocol
/// ---
/// <!--
var Syndicate = require('../../src/main.js');
/// -->
/// This is an extended two-buyer book-purchase protocol, based
/// loosely on an example given in:
///
/// > K. Honda, N. Yoshida, and M. Carbone, “Multiparty asynchronous
/// > session types,” POPL 2008.
/// # The Scenario
///
/// A book-seller responds to requests for book prices when asked. A
/// pair of prospective buyers run through a shopping list. For each
/// book, the first buyer offers to split the cost of the book with
/// the second. If the second has enough money left, it accepts;
/// otherwise, it rejects the offer, and the first buyer tries a
/// different split. If the second buyer agrees to a split, it then
/// negotiates the purchase of the book with the book-seller.
/// # The Protocol
/// ## Role: SELLER
///
/// - when interest in `bookQuote($title, _)` appears,
/// asserts `bookQuote(title, Maybe Float)`, `false` meaning not available,
/// and otherwise an asking-price.
/// - when interest in `order($title, $offer-price, _, _)` appears,
/// asserts `order(title, offer-price, false, false)` for "no sale", otherwise
/// `order(title, offer-price, PositiveInteger, String)`, an accepted sale.
/// ## Role: BUYER
///
/// - observes `bookQuote(title, $price)` to learn prices.
/// - observes `order(title, offer-price, $id, $delivery-date)` to make orders.
/// ## Role: SPLIT-PROPOSER
///
/// - observes `splitProposal(title, asking-price, contribution, $accepted)`
/// to make a split-proposal and learn whether it was accepted or not.
/// ## Role: SPLIT-DISPOSER
///
/// - when interest in `splitProposal($title, $asking-price, $contribution, _)`
/// appears, asserts `splitProposal(title, askingPrice, contribution, true)`
/// to indicate they are willing to go through with the deal, in which case
/// they then perform the role of BUYER for title/asking-price, or asserts
/// `splitProposal(title, asking-price, contribution, false)` to indicate they
/// are unwilling to go through with the deal.
/// # A Sample Run
///
/// Run the program with `../../bin/syndicatec index.js | node` from a
/// checkout of the Syndicate repository.
///
/// A learns that the price of Catch 22 is 2.22
/// A makes an offer to split the price of Catch 22 contributing 1.11
/// B is being asked to contribute 1.11 toward Catch 22 at price 2.22
/// B accepts the offer, leaving them with 3.8899999999999997 remaining funds
/// A learns that the split-proposal for Catch 22 was accepted
/// A learns that Encyclopaedia Brittannica is out-of-stock.
/// The order for Catch 22 has id 10001483, and will be delivered on March 9th
/// A learns that the price of Candide is 34.95
/// A makes an offer to split the price of Candide contributing 17.475
/// B is being asked to contribute 17.475 toward Candide at price 34.95
/// B hasn't enough funds (3.8899999999999997 remaining)
/// A learns that the split-proposal for Candide was rejected
/// A makes an offer to split the price of Candide contributing 26.212500000000002
/// B is being asked to contribute 8.7375 toward Candide at price 34.95
/// B hasn't enough funds (3.8899999999999997 remaining)
/// A learns that the split-proposal for Candide was rejected
/// A makes an offer to split the price of Candide contributing 30.581250000000004
/// B is being asked to contribute 4.368749999999999 toward Candide at price 34.95
/// B hasn't enough funds (3.8899999999999997 remaining)
/// A learns that the split-proposal for Candide was rejected
/// A makes an offer to split the price of Candide contributing 32.765625
/// B is being asked to contribute 2.184375000000003 toward Candide at price 34.95
/// B accepts the offer, leaving them with 1.7056249999999968 remaining funds
/// A learns that the split-proposal for Candide was accepted
/// A learns that the price of The Wind in the Willows is 3.95
/// A makes an offer to split the price of The Wind in the Willows contributing 1.975
/// The order for Candide has id 10001484, and will be delivered on March 9th
/// B is being asked to contribute 1.975 toward The Wind in the Willows at price 3.95
/// B hasn't enough funds (1.7056249999999968 remaining)
/// A learns that the split-proposal for The Wind in the Willows was rejected
/// A makes an offer to split the price of The Wind in the Willows contributing 2.9625000000000004
/// B is being asked to contribute 0.9874999999999998 toward The Wind in the Willows at price 3.95
/// B accepts the offer, leaving them with 0.718124999999997 remaining funds
/// A learns that the split-proposal for The Wind in the Willows was accepted
/// A has bought everything they wanted!
/// The order for The Wind in the Willows has id 10001485, and will be delivered on March 9th
/// # The Code
/// ## Type Declarations
/// First, we declare *assertion types* for our protocol.
assertion type bookQuote(title, price);
assertion type order(title, price, id, deliveryDate);
assertion type splitProposal(title, price, contribution, accepted);
/// ## Utilities
/// This routine is under consideration for possible addition to the
/// core library.
///
function whileRelevantAssert(P) {
react {
assert P;
} until {
case retracted Syndicate.observe(P);
}
}
/// ## Implementation: SELLER
function seller() {
actor {
/// We give our actor two state variables: a dictionary recording our
/// inventory of books (mapping title to price), and a counter
/// tracking the next order ID to be allocated.
this.books = {
"The Wind in the Willows": 3.95,
"Catch 22": 2.22,
"Candide": 34.95
};
this.nextOrderId = 10001483;
/// The seller responds to interest in bookQuotes by asserting a
/// responsive record, if one exists.
react {
during Syndicate.observe(bookQuote($title, _)) {
assert bookQuote(title, title in this.books ? this.books[title] : false);
}
}
/// It also responds to order requests.
react {
on asserted Syndicate.observe(order($title, $offerPrice, _, _)) {
/// We cannot sell a book we do not have, and we will not sell for
/// less than our asking price.
var askingPrice = title in this.books ? this.books[title] : false;
if ((askingPrice === false) || (offerPrice < askingPrice)) {
whileRelevantAssert(order(title, offerPrice, false, false));
} else {
/// But if we can sell it, we do so by allocating an order ID and
/// replying to the orderer.
var orderId = this.nextOrderId++;
delete this.books[title];
actor {
whileRelevantAssert(order(title, offerPrice, orderId, "March 9th"));
}
}
}
}
}
}
/// ## Implementation: SPLIT-PROPOSER and book-quote-requestor
function buyerA() {
actor {
var self = this;
/// Our actor remembers which books remain on its shopping list, and
/// tries to buy them one at a time, sharing costs with `buyerB`.
self.titles = ["Catch 22",
"Encyclopaedia Brittannica",
"Candide",
"The Wind in the Willows"];
/// JavaScript's callback-oriented blocking means that we express our
/// loop in almost a tail-recursive style, using helper functions
/// `buyBooks` and `trySplit`.
buyBooks();
function buyBooks() {
if (self.titles.length === 0) {
console.log("A has bought everything they wanted!");
return;
}
var title = self.titles.shift();
/// First, retrieve a quote for the title, and analyze the result.
react until {
case asserted bookQuote(title, $price) {
if (price === false) {
console.log("A learns that "+title+" is out-of-stock.");
buyBooks();
} else {
console.log("A learns that the price of "+title+" is "+price);
/// Next, repeatedly make split offers to a SPLIT-DISPOSER until
/// either one is accepted, or the contribution from the
/// SPLIT-DISPOSER becomes pointlessly small. We start the process by
/// offering to split the price of the book evenly.
trySplit(title, price, price / 2);
}
}
}
}
function trySplit(title, price, contribution) {
console.log("A makes an offer to split the price of "+title+
" contributing "+contribution);
/// If we are about to offer to split the price, but the other buyer
/// would contribute less than 10c, then it's not worth bothering; we
/// may as well buy it ourselves. Another version of the program could
/// perform the BUYER role here.
if (contribution > (price - 0.10)) {
console.log("A gives up on "+title+".");
buyBooks();
} else {
/// Make our proposal, and wait for a response.
react until {
case asserted splitProposal(title, price, contribution, true) {
console.log("A learns that the split-proposal for "+title+" was accepted");
buyBooks();
}
case asserted splitProposal(title, price, contribution, false) {
console.log("A learns that the split-proposal for "+title+" was rejected");
trySplit(title, price, contribution + ((price - contribution) / 2));
}
}
}
}
}
}
/// ## Implementation: SPLIT-DISPOSER and BUYER
function buyerB() {
actor {
/// This actor maintains a record of the amount of money it has left
/// to spend.
this.funds = 5.00;
/// It spends its time waiting for a SPLIT-PROPOSER to offer a
/// `splitProposal`.
react {
on asserted Syndicate.observe(splitProposal($title, $price, $theirContribution, _)) {
var myContribution = price - theirContribution;
console.log("B is being asked to contribute "+myContribution+" toward "+title+
" at price "+price);
/// We may not be able to afford contributing this much.
if (myContribution > this.funds) {
console.log("B hasn't enough funds ("+this.funds+" remaining)");
whileRelevantAssert(splitProposal(title, price, theirContribution, false));
} else {
/// But if we *can* afford it, update our remaining funds and spawn a
/// small actor to handle the actual purchase now that we have agreed
/// on a split.
var remainingFunds = this.funds - myContribution;
console.log("B accepts the offer, leaving them with "+remainingFunds+" remaining funds");
this.funds = remainingFunds;
actor {
react {
/// While waiting for order confirmation, take the opportunity to
/// signal to our SPLIT-PROPOSER that we accepted their proposal.
assert splitProposal(title, price, theirContribution, true);
/// When order confirmation arrives, this purchase is completed.
} until {
case asserted order(title, price, $id, $date) {
console.log("The order for "+title+" has id "+id+
", and will be delivered on "+date);
}
}
}
}
}
}
}
}
/// ## Starting Configuration
ground dataspace {
seller();
buyerA();
buyerB();
}