ProtocolJS

A JavaScript port of Clojure's protocol polymorphism.

Inspiration and Attribution

ProtocolJS is an informal fork of Gozala's protocol module with some variation in implementation to

• Make it compatible across more browsers.
• Make it more robust to using serialized objects with the library between runtime restarts.
• Reflect other stylistic opinions.

Installation

$ npm install protocoljs

Documentation

A protocol is a set of function interfaces.

var protocol = require('protocoljs');

// Here, we implement the functions' interfaces, not their implementations
var Enumerable = protocol({
  first: [protocol] // Here protocol is a placeholder for the typed argument
, rest: [protocol]
, repeat: [Number, protocol] // The typed argument does not need to be first
});

Protocols enable polymorphism in a flexible way where the interface definition is decoupled from the implementations for any number of types.

Enumerable(Array, {
  first: function (array) {
    return array[0];
  }
, rest: function (array) {
    return array.slice(1);
  }
, repeat: function (times, array) {
    var result = [];
    while (times--) {
      result = result.concat(array);
    }
    return result;
  }
});

Enumerable.first([1, 2, 3]); // => 1
Enumerable.rest([1, 2, 3]); // => [2, 3]
Enumerable.repeat(2, [1, 2, 3]); // => [1, 2, 3, 1, 2, 3]

You can tie any number of types to a protocol.

Enumerable(String, {
  first: function (string) {
    return string.charAt(0);
  }
, rest: function (string) {
    return string.substring(1);
  }
, repeat: function (times, string) {
    var result = '';
    while (times--) {
      result += string;
    }
    return result;
  }
});

Enumerable.first('abc'); => 'a'
Enumerable.rest('abc'); => 'bc'
Enumerable.repeat(2, 'abc'); => 'abcabc'

You can also tie any number of protocols to a type.

var RightEnumerable = protocol({
  first: [protocol]
, rest: [protocol]
});

RightEnumerable(String, {
  first: function (string) {
    return string.charAt(string.length-1);
  }
, rest: function (string) {
    return string.substring(0, string.length-1);
  }
});

RightEnumerable.first('abc'); // => 'c'
RightEnumerable.rest('abc'); // => 'ab'

Another cool feature is re-opening protocols to extend their interfaces.

protocol(Enumerable, {
  slice: [protocol, Number, Number]
});

Enumerable(Array, {
  slice: function (array, start, end) {
    return array.slice(start, end);
  }
});

Enumerable(String, {
  slice: function (string, start, end) {
    return string.substring(start, end);
  }
});

Enumerable.slice([1, 2, 3], 0, 2); => [1, 2]
Enumerable.slice('abc', 0, 2); => 'ab'

But protocols can be associated with more than just built-in types such as Number, Array, String, and other native types. You can also implement a protocol for custom constructors that you create, as long as you assign a special protocolId that is unique across types.

function OrderedSet (members) {
  this.members = members || [];
}

OrderedSet.prototype.protocolId = 'Set';
OrderedSet.prototype.add = function (member) {
  var members = this.members;
  for (var i = members.length; i--; ) {
    if (members[i] === member) return false;
  }
  return members.push(member);
};

OrderedSet.prototype.remove = function (member) {
  var members = this.members;
  for (var i = members.length; i--; ) {
    if (members[i] === member) {
      members.splice(i, 1);
      return true;
    }
  }
  return false;
};

Enumerable(OrderedSet, {
  first: function (set) {
    return set.members[0];
  }
, rest: function (set) {
    return new OrderedSet(set.members.slice(1));
  }
});

var set = new OrderedSet([1, 2, 3]);

Enumerable.first(set); // => 1
Enumerable.rest(set); // => <OrderedSet [2, 3]>

MIT License

Copyright (c) 2011 by Brian Noguchi and Nate Smith

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.