continuation.js

continuation.js

Continuation support for Node.js

• It converts JavaScript code into Continuation Passing Style (CPS) code in a best effort manner.
• No new syntax or keyword is required.
• Fallback mechanism when CPS is not possible or not implemented.
• Tail calls are properly handled.

How to use

From github

% git clone https://github.com/dai-shi/continuation.js.git
% ./bin/continuation-compile sample/fact.js > cps_fact.js

% cat sample/fact.js
function fact(x) {
  function fact_tail(x, r) {
    if (x === 0) {
      return r;
    } else {
      return fact_tail(x - 1, x * r);
    }
  }
  return fact_tail(x, 1);
}

% node -e "console.log(require('./sample/fact.js').fact(100000))"

.../continuation.js/sample/fact.js:2
  function fact_tail(x, r) {
                        ^
RangeError: Maximum call stack size exceeded

% node -e "console.log(require('./cps_fact.js').fact(100000))"
Infinity

How it works

• 4 classes are defined in the global scope.
  • CpsFunction
  • CpsContinuation
  • CpsResult
  • CpsRun
• CPS enabled functions have the CpsEnabled=true property.
• Traversing AST to transform into CPS, only when possible!
• Keeping original code so that non-CPS is always possible.

Limitations

• There are some overhead, obviously.
• Not all calls are transformed into CPS.
• Arguments objects are handled, but it may cause some problems.
• Maybe some more.

TODOs

• Integrate with Node.js module system.
• Better documents.
• Transform non-tail calls into CPS.
• More tests.
• Avoid duplicating functions.
• Fix ugly code.

Author

Daishi Kato @dai_shi