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Screenshot of the Squeak VM running under X11.

The Squeak programming language is a Smalltalk implementation, derived directly from Smalltalk-80 by a group at Apple Computer that included some of the original Smalltalk-80 developers. Its development was continued by the same group at Walt Disney Imagineering, where it was intended for use in internal Disney projects. Some Squeak users refer to Squeak as a programming language rather than as a Smalltalk implementation. It is object-oriented, class-based, and reflective. Squeak is available for many platforms, and programs produced on one platform run bit-identical on all other platforms. The Squeak system includes code for generating a new version of the virtual machine (VM) on which it runs. It also includes a VM simulator written in itself (Squeak). For this reason, it is easily ported.

Developers

Dan Ingalls is one of the important contributors to the Squeak project. Ingalls wrote the paper "Back to the Future: the story of Squeak, a practical Smalltalk written in itself", as well as built the architecture for five generations of the Smalltalk language upon which Squeak is built. Squeak incorporates many of the elements Alan Kay proposed in the Dynabook concept, which he formulated in the 1960s. Kay is an important contributor to the Squeak project. Andreas Raab seems to have the most commits.

User interface frameworks

Squeak includes a number of user interface frameworks:

• An implementation of Morphic, Self's graphical direct manipulation interface framework. This is Squeak's main interface.
• Tile-based, limited visual programming scripting in Etoys, based on Morphic.
• A new, experimental interface called Tweak. In 2001, it became clear that the Etoy architecture in Squeak had reached its limits in what the Morphic interface infrastructure could do. Hewlett-Packard researcher Andreas Raab proposed defining a "script process" and providing a default scheduling mechanism that avoids several more general problems.^[1] The result was a new user interface, proposed to replace the Squeak Morphic user interface in the future. Tweak added mechanisms of islands, asynchronous messaging, players and costumes, language extensions, projects, and tile scripting.^[2] Its underlying object system is class-based, but to users, during programming (scripting), it acts like it is prototype-based. Tweak objects are created and run in Tweak project windows.
• MVC, derived from the original Smalltalk-80 user interface framework which first introduced and popularized the Model-View-Controller architectural pattern^[3] (so named after the three core classes of the framework). Thus, the term "MVC" in the context of Squeak refers to both one of the available user interface frameworks and the pattern the framework follows. MVC is provided for programmers who wish to use this older type of interface.

Uses

Many Squeak contributors collaborate on Open Cobalt, a free and open source virtual world browser and construction toolkit application which is built on Squeak.

Squeak is also used in the es operating system and for implementing the Scratch programming language for beginning programmers.

License

Squeak may be downloaded at no cost, including all its source code. Unlike other languages, Squeak is distributed in a prebuilt virtual machine image form rather than bootstrappable source code.

There is some debate as to whether the Squeak license qualifies as free software or not, due to the presence of an indemnity clause in the original Squeak License. Version 1.1 of the environment, originally released on October 1997 under the Squeak License, has been released in May 2006 under the free and open source Apple Public Source License. It has been relicensed under the Apache License allowing inclusion in the One Laptop Per Child initiative.^[4]

See also

• Open Cobalt
• Croquet project
• Seaside
• Scratch
• Alice
• Etoys
• SqueakNOS
• Pharo

References

1. ^ http://tweakproject.org/ABOUT/FAQ/OriginalTweakMemo/
2. ^ http://tweakproject.org/TECHNOLOGY/Whitepapers/
3. ^ http://st-www.cs.uiuc.edu/users/smarch/st-docs/mvc.html
4. ^ http://laptop.media.mit.edu/laptopnews.nsf/2e76a5a80bc36cbf85256cd700545fa5/fd078b45d9ffd8e7852571f9005be555?OpenDocument

External links

• Squeak.org
• Squeak Swiki
• Back to the future: the story of Squeak, a practical Smalltalk written in itself (HTML versions:[1][2])
• Squeakland.org
• SqueakNotes
• Learning Squeak at c2.com
• Search engine related to Squeak
• EtoysIllinois Champaign, IL
• (Spanish) Small-Land.org
• Squeak at the Open Directory Project
• Pharo

Books

• Squeak by Example Squeak by Example is a new open-source book about the Squeak development environment.
• Downloadable books about Smalltalk Permission obtained to make these books freely available. Over a dozen full texts scanned from print.)
• Programando con Smalltalk - Un ambiente de objetos vivos Book in Spanish by Diego Gomez Deck.
• Squeak: Object-Oriented design With Multimedia Applications, by Mark Guzdial