GNU Smalltalk

GNU Smalltalk
Name	GNU Smalltalk
Developer	GNU Project
Released	12 December 1992
Latest release version	3.2.5
Latest release date	19 August 2013
Operating system	Cross-platform
Genre	Programming language
License	LGPL and GPL
Website	https://www.gnu.org/software/smalltalk/

GNU Smalltalk is an implementation of the Smalltalk programming language developed by the GNU Project. It provides a largely ANSI Smalltalk-compliant environment, emphasizing a traditional interpreter and scripting capabilities rather than a full integrated development environment. The system is notable for its tight integration with the Unix and Linux command-line, allowing it to be used effectively for system administration tasks and text processing.

Overview

GNU Smalltalk was initiated in the early 1990s as part of the broader free software movement championed by Richard Stallman. Unlike other implementations such as Squeak or Pharo, it was designed from the outset to function as a standalone interpreter, integrating seamlessly with the GNU toolchain and existing Unix philosophy. The project aimed to provide a free, portable Smalltalk system that could be used for both application development and as an extension language, similar to how Perl or Python are employed. Its development has been closely associated with the Free Software Foundation, ensuring its availability under copyleft licenses.

Features

The system includes a comprehensive class library that covers areas from data structures to network programming. A key feature is its powerful foreign function interface, which simplifies calling routines from C libraries and interacting with the underlying operating system. It supports reflection and metaprogramming capabilities inherent to the Smalltalk language, along with automatic memory management. For scripting, it offers robust regular expression support and file system access, making it suitable for automating tasks on Solaris, BSD, and Linux distributions. The environment also includes a bytecode compiler and a virtual machine for efficient execution.

Implementation

The interpreter and virtual machine are written primarily in C, ensuring portability across various architectures. The object memory system uses a snapshot mechanism to save the state of a running program. Unlike image-based systems, GNU Smalltalk can compile source code directly into bytecode for the virtual machine, and it can also parse Smalltalk-80 syntax files. Its foreign function interface leverages libffi to facilitate calls to external shared libraries, and the system integrates with GNU Autoconf for building on different platforms. The runtime system is designed to be lightweight and linkable into other applications.

Development and community

Primary development has been stewarded by volunteers within the GNU Project, with notable contributions from early maintainers like Steve Byrne. The project uses GNU Savannah for version control and bug tracking, following the collaborative model typical of free and open-source software. Discussions occur on mailing lists and within the broader Smalltalk community, which includes users of VisualWorks and Dolphin Smalltalk. While not as actively developed as Pharo, releases have focused on stability, ANSI Smalltalk compliance, and porting to new systems like MacOS and Microsoft Windows. The community values its role in providing a command-line oriented Smalltalk for the GNU system.

Example code

A simple program to print "Hello, World!" demonstrates the scripting orientation, resembling the syntax of Perl or Ruby. More complex examples might involve defining new subclasses of Collection or using the Socket API for network communication. The language's block syntax is used for control flow and iteration, similar to constructs in Ruby and JavaScript. Code can be executed interactively via the REPL or from script files, integrating with shell scripts through the shebang line.

Comparison with other Smalltalk implementations

Unlike the image-based persistence model of Squeak or VisualWorks, GNU Smalltalk typically operates on source code files, aligning it more with Python and Perl. It lacks the extensive graphical user interface frameworks found in Pharo or Dolphin Smalltalk, focusing instead on server-side and text-based user interface applications. While Amber Smalltalk targets web browsers, and Cincom Smalltalk emphasizes commercial deployment, GNU Smalltalk's niche is Unix shell integration and system programming. Its license terms, under the GNU General Public License, differ from the MIT License used by Squeak or the Apache License of some derivatives.

Category:GNU Project software Category:Smalltalk programming language family Category:Free software programmed in C Category:Scripting languages Category:1992 software