Smalltalk

Smalltalk. It is a purely object-oriented programming language, dynamic language, and integrated development environment, originally created at the Xerox PARC research center in the 1970s. The language was designed around the concepts of message passing and live coding, profoundly influencing the development of modern software engineering and graphical user interface design. Its pioneering environment introduced now-ubiquitous ideas like the Model–view–controller architecture and overlapping window management.

History

The project was initiated by Alan Kay's Learning Research Group at Xerox PARC, building upon ideas from Simula and Lisp (programming language). Key contributors included Dan Ingalls, Adele Goldberg, and Ted Kaehler. The first version, later known as Smalltalk-72, was operational by 1972. Major revisions culminated in the widely distributed Smalltalk-80 system, which was released to University of California, Berkeley and Hewlett-Packard, cementing its influence beyond the Xerox Alto. The seminal book "Smalltalk-80: The Language and Its Implementation" by Adele Goldberg and David Robson became a foundational text. Despite its origins in a corporate lab, the language fostered a dedicated academic and commercial community, with pivotal work continuing at places like the Apple Computer Advanced Technology Group and Digitalk.

Language overview

In its syntax, everything is an object, from integers and booleans to classes and blocks of code, all communicating via message passing. Control structures like conditionals and loops are implemented through messages to Boolean objects and Block (programming) objects, rather than built-in keywords. The language employs a single inheritance (object-oriented programming) model and is dynamically typed, with all type checking done at runtime (program lifecycle). Its reflective capabilities allow programs to examine and modify their own structure, a concept influential in metaprogramming. Code is typically organized into packages called Monticello (file format), and the system image contains all live objects.

Development environment

The programming experience is centered on a fully integrated, live programming system where code and objects persist in a snapshot (computer storage) known as an image. Programmers interact with the system via a graphical user interface featuring overlapping windows, pop-up context menus, and a system browser (computing) for navigating code. This environment, first realized on the Xerox Alto, directly inspired the Apple Macintosh and subsequent desktop metaphor interfaces. The Model–view-controller pattern was invented here to structure applications. Tools within the image include a debugger, object inspector, and change list, all manipulable as objects themselves, enabling powerful refactoring and software maintenance.

Influence and legacy

Its concepts became the bedrock for modern object-oriented programming. Objective-C and Brad Cox were directly inspired by its messaging semantics. Java (programming language)'s virtual machine and garbage collection (computer science) owe a significant debt, as do the designs of Ruby (programming language) and Python (programming language). The Graphical user interface and windowing system of the Xerox Star and, by extension, the Apple Lisa and Microsoft Windows, were derived from this research. Key software patterns like Model–view-controller and design patterns originated in the Xerox PARC community. The Self (programming language) project, which influenced JavaScript and Java (programming language) optimization, was a direct descendant.

Implementations

The original Smalltalk-80 system spawned numerous commercial and open-source variants. Early significant commercial versions included Smalltalk/V from Digitalk and VisualWorks from ParcPlace Systems. The open-source Squeak project, led by Dan Ingalls and later Alan Kay, became a major platform for research and education, giving rise to Etoys (programming language) and the One Laptop per Child initiative. Pharo is a popular, clean-slate fork of Squeak focused on modern software development. Other notable implementations include GNU Smalltalk, which offers a more traditional scripting language experience, Dolphin Smalltalk for Microsoft Windows, and Amber Smalltalk, which compiles to JavaScript.

Category:Programming languages Category:Object-oriented programming languages Category:Dynamically typed programming languages