The Mesa programming environment

People everywhere are developing multi-window, integrated programming environments for their favorite computers and languages. This paper describes the Mesa programming facilities of the Xerox Development Environment (XDE). It is interesting for several reasons. It has existed in something similar to its current form for about 5 years. It has more than 500 users, many interacting with it 8 or more hours a day. Several million lines of code have been written by these users, including large, multi-author systems.

Previous papers have dealt with the Mesa language [Geschke77, Mitchell79], the operating system [Redell79, Lampson80] and the processor architecture on which it runs [Johnsson82, Sweet82]. This paper describes the programming environment: the user illusion, the set of programming tools, and the facilities available for augmenting the environment. Section 2 gives a short history of the environment, including some of our original design goals. Section 3 describes the current state of the user interface and discusses a few of the schemes that were tried and discarded. Section 4 describes some of the program development tools available and discusses how features of the language have influenced their design, and indeed influenced what tools are in the set. Section 5 describes other tools that, although valuable to the programming task, are largely language independent. Section 6 talks about how easy it is to make additions to the system, and gives examples of user additions—some that modify the environment and some that simply provide new tools. Section 7 discusses what we feel are major successes and what we feel needs to be done in the future.