rafa/src/core/UntilEnumerator.js

Rafa.js is a Javascript framework for building concurrent applications.

// # constructor(generator: () => A, stopValue: A): UntilEnumerator
// An Enumerator that calls a generator function for each value and assumes the
// generator is done producing values when the value returned equals stopValue.
// The default for stopValue is undefined (essentially call this without 
// providing a stopValue argument).
function UntilEnumerator(generator, stopValue) {
  this.generate = generator;
  this.stop = stopValue;
}

inherit(UntilEnumerator, Enumerator, {
  // # next(callback: A => _)
  // Execute a callback function, passing the next value wrapped in a Message.
  // The next value is created by calling the generate method. If the value
  // returned from the generate method is equal to the stop property, then
  // a DoneMessage is sent to the callback.
  next(callback) {
    if (!this.generate) throw this.CompleteError;
    const a = this.generate();
    let M = this.Message;
    if (a === this.stop) {
      this.generate = null;
      this.stop = null;
      M = this.DoneMessage;
    }
    else if (a instanceof Error)
      M = this.ErrorMessage;

    callback(new M(a));
  }
});