Tcl in AltaVista Forum

AltaVista Forum is an award-winning collaboration environment based on the open technologies of the World-Wide Web and built on the foundation of the Tcl language [pob]. Using Tcl’s inherent extensibility the AltaVista Forum toolkit provides a simple class/inheritance mechanism, an information manager customized for the data storage needs of collaboration applications, and a growing toolkit for creating asynchronous collaboration applications on the Web. This paper details how Tcl has been employed as the basis of a commercial web-based collaboration environment. While the focus of the paper will be on the design and our use of Tcl in AltaVista Forum 98, we will also touch on how the design has evolved over the past three releases of the product. Selecting the Tcl Language AltaVista Forum (formerly Workgroup Web Forum) is described pretty thoroughly from a functional standpoint in [Chiu]. If all has gone well, we will have released the third version of this product since its debut in 1995: spanning the use of Tcl 7.3 through 7.6 (and looking forward to Tcl 8). (More information can be found at: http://www.altavista.software.digital.com/forum) In late 1994 a small team of engineers in Digital’s Networks group began pursuing two goals: building products which worked within the framework of the then emerging World-Wide Web and building them in a new way which matched the rapid pace of evolution expected in this space. Rapid development, flexibility, and platform independence pointed us towards interpreted languages as a core technology for constructing these new products. Perl, Python, Tcl, and a number of other interpreters were examined and evaluated. Tcl emerged as the tool of choice and in a matter of weeks a toolbox of extensions began to come together along with a flurry of prototypes. The selection of Tcl as a core technology came about as a compromise based on a variety of factors and, to be sure, a bit of cultural pressure within Digital. For example, Perl was arguably more popular and therefore would be more attractive to people who wanted to program in our environment. Python had a very attractive object model and reasonably clean extension mechanism. Tcl was selected because it was a mature (version 7 and still cooking), portable (most UNIX platforms, Windows, and Macintosh), and highly extensible language that possessed a vibrant user community (comp.lang.tcl), an excellent book available in most bookstores [Ousterhout], and (as luck would have it) a commitment of support by a respected engineering company (Sun Microsystems). We’ve been generally happy with our choice. Initial Design Elements Following in the footsteps of Tk (and others) we created the concept of the AltaVista Forum “Toolkit”: a custom scripting language for developing a class of web-based collaborative applications. Using Tcl as the core language we extended it with both public domain and privately developed code. The goal was to develop a language that was sufficiently powerful so that simple collaborative applications could be scripted in just a few pages, but would also allow for the development of sophisticated and customizable applications as well. We also wanted to provide a language which would execute identically on multiple target platforms (specifically UNIX and Windows NT) while not excluding the ability to use Tcl to its fullest extent (we don’t disable any commands, including exec),