Squeak

The Squeak programming language is a dialect of Smalltalk. 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. Later on the group moved on to be supported by HP labs, SAP Labs and most recently Y Combinator.

Squeak is cross-platform. Programs produced on one platform run bit-identical on all other platforms, and versions are available for many platforms including the obvious Windows/macOS/linux versions. 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 Squeak. For these reasons, it is easily ported.

Developers

Dan Ingalls, an important contributor to the Squeak project, wrote the paper^[3] 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 four 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 novel, 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.^[4] This resulted in 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.^[5] 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.
• A model–view–controller (MVC) interface was the primary UI in Squeak versions 3.8 and earlier. It derived from the original Smalltalk-80 user interface framework which first introduced and popularized the MVC architectural pattern.^[6] MVC takes its name from 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 still 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 Nintendo ES operating system^[7] 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.^[8]

License

Squeak 4.0 and later 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^[9] and has attained official approval from the Open Source Initiative^[10] 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 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.^[11]

Squeak virtual machine

The Squeak virtual machine is a family of virtual machines (VMs) used in Smalltalk programming language implementations. They are an essential part of any Smalltalk implementation. All are open-source software. The current VM is a high performance dynamic translation system. The relevant code is maintained on GitHub at OpenSmalltalk

External links

• CogVM
• RoarVM

See also

• List of open-source programming languages
• Alice (software)
• Croquet Project
• Pharo
• Seaside (software)

References

External links

Wikimedia Commons has media related to Squeak.

• Official website
• Squeak at DMOZ