squeak

Squeak

Screenshot of Squeak running under X11.
Original author(s)	Alan Kay, Dan Ingalls, Adele Goldberg
Developer(s)	Alan Kay, Dan Ingalls, Ted Kaehler, Scott Wallace, John Maloney, Andreas Raab, Mike Rueger
Initial release	1996
Stable release	4.3 / December 23, 2011; 4 months ago (2011-12-23)
Operating system	Cross-platform (multi-platform): Unix-like, Mac OS X, iOS, Windows, more
Type	Smalltalk virtual machine, development environment
License	MIT license
Website	www.squeak.org

The Squeak programming language is a Smalltalk implementation. It is object-oriented, class-based and reflective.

It was 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.

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, an important contributor to the Squeak project, wrote the paper^[1] upon which Squeak is built and constructed the architecture for five generations of the Smalltalk language.

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.

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.^[2] 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.^[3] 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.
• In Squeak versions 3.8 and earlier, the MVC interface. It is derived from the original Smalltalk-80 user interface framework which first introduced and popularized the model-view-controller architectural pattern^[4] (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 was provided for programmers who wished 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. In May 2011 the OpenQwaq virtual conferencing and collaboration system based on Squeak, an open source release of Teleplace, was announced on the Teleplace blog.^[5]

License

Squeak 4.0 may be downloaded at no cost, including source code, as a prebuilt virtual machine image licensed under the MIT License, with the exception of some of the original Apple code, which is governed by the Apache License.

Originally, Apple actually released Squeak under a license called the "Squeak License." While source code was available and modification permitted, the Squeak License contained an indemnity clause that prevented it from qualifying as true Free and Open Source Software.

In 2006, Apple relicensed Squeak twice. First, in May, Apple used its own Apple Public Source License, which satisfies the Free Software Foundation's concept of a Free Software License ^[6] and has attained official approval from the Open Source Initiative^[7] as an Open Source License. The Apple Public Source License, as it turns out, fails to pass the third standard that Free and Open Source Software licenses are held to: the Debian Free Software Guidelines promulgated by the Debian project, an influential volunteer-run GNU/Linux distribution. To enable inclusion of Etoys in the One Laptop Per Child project, a second relicensing was undertaken using the Apache License. At this point, an effort was also made to address the issue of code contributed by members of the Squeak community, which it was not in Apple's power to unilaterally relicense.

For each contribution made under the Squeak License since 1996, a relicensing statement was obtained authorizing distribution under the MIT license, and finally in March 2010, the end result was released as Squeak 4.0, now under combined MIT and Apache licenses.^[8]

See also

• Open Cobalt
• Croquet project
• OpenQwaq
• Seaside
• Scratch
• Alice
• Etoys
• Pharo
• List of open-source programming languages

References

1. ^ Ingalls, Dan; Kaehler, Ted; Maloney, John; Wallace, Scott; Kay, Alan (1997). "Back to the Future: the story of Squeak, a practical Smalltalk written in itself". ACM Digital Library. http://portal.acm.org/citation.cfm?id=263754&coll=portal&dl=ACM. Retrieved 2011-06-12. 
2. ^ "Tweak: OriginalTweakMemo". Tweakproject.org. 2001-07-06. http://tweakproject.org/ABOUT/FAQ/OriginalTweakMemo/. Retrieved 2011-06-12. 
3. ^ "Tweak: Whitepapers". Tweakproject.org. http://tweakproject.org/TECHNOLOGY/Whitepapers/. Retrieved 2011-06-12. 
4. ^ Burbeck, Steve (1997-04-04). "How to use Model-View-Controller (MVC)". St-www.cs.uiuc.edu. http://st-www.cs.uiuc.edu/users/smarch/st-docs/mvc.html. Retrieved 2011-06-12. 
5. ^ "Moving Immersive Collaboration Forward". http://teleplace.wordpress.com/2011/05/03/moving-immersive-collaboration-forward/. 
6. ^ "FSF's Opinion on the Apple Public Source License (APSL) 2.0". Gnu.org. 2011-05-07. http://www.gnu.org/philosophy/apsl.html. Retrieved 2011-06-12. 
7. ^ "Clarification of the APSL: Press Releases OS Clarifies The Status Of The APSL". Opensource.org. 1999-03-17. http://www.opensource.org/pressreleases/osi-clarifies-APSL.php. Retrieved 2011-06-12. 
8. ^ "Squeak 4.0 released - now under MIT/Apache license". The H Open. 2010-03-16. http://www.h-online.com/open/news/item/Squeak-4-0-released-now-under-MIT-Apache-license-956267.html. Retrieved 2011-06-12. 

External links

• Official website
• 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
• EtoysIllinois Champaign, IL
• (Spanish) Small-Land.org
• OpenQwaq website
• Squeak at the Open Directory Project
• Pharo
• RoarVM, a multi- and manycore VM for Squeak

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