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Flexible Scheme objects with prototypes and message passing
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README.org

Protolk

Flexible Scheme objects with message passing and prototypes

About Protolk

Protolk provides flexible object oriented programming in Scheme, combining encapsulation and message passing a la Smalltalk and Ruby, with prototypal inheritance a la Self and JavaScript.

Protolk is not a new language or dialect. It offers a Scheme record type, and collection of procedures that can be seamlessly integrated with other Scheme code. Some optional reader extensions are also available, to add some syntax sugar for convenience.

Protolk is designed with four core principles in mind:

  • Simplicity: Protolk’s object model is very simple: an object holds its own properties and methods, it inherits properties and methods from an (optional) base object, and it performs actions in response to messages. That’s all there is to it. However…
  • Extensibility: … it’s easy to build complex and interesting behavior on top of that simple object model. You can extend, customize, or replace pretty much anything about Protolk, including much of the inheritance system!
  • Flexibility: Objects can be modified in any way at any time. You don’t have to declare ahead of time what properties or methods an object will have, or redefine an entire class just to add a property or method to a single object.
  • Encapsulation: Objects maintain a separation between their private state and their public interfaces. Properties are only (directly) read or written by the object itself. Methods are public by nature, but there are ways to implement private methods.

Installation and Usage

You currently need Chicken Scheme to use Protolk. After you have installed Chicken, you can install the latest release of Protolk by running chicken-install protolk. Or, if you want the absolute latest revision of Protolk, you can clone the git repository then run the chicken-install command from within the repository clone directory.

To use Protolk in your code:

(require-extension protolk
                   protolk-stdpob
                   protolk-syntax-send-brackets
                   protolk-syntax-own-prop-at)

When you compile the file, if you are using Protolk’s syntax sugar, you will need to tell the compiler to load the syntax modules as compiler extensions:

csc -X protolk-syntax-send-brackets -X protolk-syntax-own-prop-at  your-code.scm

If you don’t want to use syntax sugar, you don’t need those flags, and you can omit the syntax modules from the require-extension expression shown above.

For working code samples, see the files in the demo directory.

Caveats

As of November 2012, Protolk is still just an experiment. I make no guarantees about its performance, efficiency, stability, security, correctness, usefulness, or cleverness. Think twice (or thrice) before using Protolk in production code.

Be aware that Protolk is based on synchronous (blocking) message passing, implemented as procedure calls. No special consideration has been given to issues of concurrency, threading, or asynchronicity. So, Protolk probably does not offer any special benefit for distributed or parallel computing. (But, Protolk is flexible enough that you can easily create Protolk objects that implement message queues or other form of asynchronous message passing.)

Protolk is currently targeted at Chicken Scheme. If you are interested in helping to port Protolk to your favorite Scheme or Lisp, create a new issue on the Protolk issue tracker or email me.

License

Protolk is made available under the following terms (the BSD 2-Clause License):

Protolk: flexible Scheme objects with message passing and prototypes

Copyright © 2012 John Croisant. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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