Mesa: A Pioneering Language from Xerox PARC
Mesa is a programming language that emerged in the late 1970s at the Xerox Palo Alto Research Center (Xerox PARC) in Palo Alto, California, USA. It played a significant role in the development of software engineering practices and influenced the design of later languages like Modula-2 and Java. Although Mesa may not be as widely recognized as some other languages from the same era, its contributions to modular programming, exception handling, and thread synchronization left a lasting impact on the field of computer science.
The Origins of Mesa
The development of Mesa was a response to the growing needs of systems programming at Xerox PARC, which was at the forefront of research in computer science and hardware innovation at the time. The language was designed to be used on the Xerox Alto, one of the first personal computers to feature a graphical user interface (GUI). The Alto, introduced in 1973, was not only revolutionary in terms of its hardware but also in terms of the software it ran, much of which was written in BCPL (Basic Combined Programming Language). While BCPL served as a functional language for the Alto’s initial software, it lacked some critical features necessary for large-scale, modular programming, which led to the development of Mesa.
Mesa was a language heavily influenced by ALGOL, an earlier language that had a significant impact on the design of programming languages in the mid-20th century. Mesa was considered a “high-level” language, in keeping with the trend of naming languages after high-level concepts. The name “Mesa” itself was a play on the phrase “high-level” as a programming language catchphrase of the era, reflecting the goal of designing a language that was both powerful and abstract enough to support sophisticated software systems.
Features of Mesa
Mesa was primarily designed to support modular programming, a concept that emphasizes breaking down a program into independent, reusable modules. One of the key features of Mesa was its robust support for creating libraries consisting of both definition files and implementation files. A library in Mesa would have at least two parts: the definition file, which specified the interface of the library, and one or more implementation files, which contained the actual code that implemented the functions and procedures defined in the interface. This approach enforced a clear separation between the interface and the implementation, making the code more maintainable and easier to understand.
The use of separate compilation was another crucial feature of Mesa. This allowed developers to work on different parts of a program independently, ensuring that changes to one module would not require recompiling the entire program. This modular approach also facilitated the type-checking of imported entities, a feature that was relatively novel at the time. By enforcing type-checking across modules, Mesa reduced the likelihood of type errors and bugs in the system, thus improving the reliability of software written in the language.
Another important feature of Mesa was its approach to exception handling. At the time, exception handling was not widely implemented or standardized in programming languages. Mesa’s innovative mechanisms for handling software exceptions allowed the language to gracefully manage runtime errors and abnormal conditions in a manner that was both systematic and flexible. This helped create more robust programs that could handle unexpected situations without crashing or producing incorrect results.
Thread synchronization was another area in which Mesa introduced innovations. The language provided constructs to manage the execution of multiple threads concurrently, a feature that was becoming increasingly important as personal computers and workstations began to incorporate multi-tasking and parallel processing capabilities. Mesa’s thread synchronization mechanisms allowed developers to create programs that could efficiently manage concurrent tasks without the risk of race conditions or other synchronization issues.
Mesa and the Xerox Alto
Mesa was developed specifically for the Xerox Alto, a revolutionary machine for its time. The Alto featured a graphical user interface (GUI) and was designed to support multitasking, making it an ideal platform for testing and using new programming techniques. Despite this, the Alto’s system software was not written in Mesa but in BCPL, which was considered more suited for the system-level programming tasks required for the Alto’s operation. Nonetheless, Mesa was an important part of the Alto’s software ecosystem, and it would go on to influence the development of subsequent systems at Xerox PARC.
The Alto’s most famous successor, the Xerox Star workstation, used Mesa as its primary system programming language. The Xerox Star, introduced in 1981, was a precursor to modern graphical user interfaces (GUIs) and was one of the first computers to use a GUI for all its applications. The Star’s desktop environment, known as GlobalView, was built using Mesa, and the language played a key role in shaping the software infrastructure of early graphical systems.
Mesa’s contributions to graphical user interfaces and software engineering were not confined to Xerox products. The language’s design principles influenced the development of other important languages, such as Modula-2, which was created by Niklaus Wirth, and Java, which would later become one of the most widely used programming languages in the world. Both Modula-2 and Java incorporated concepts from Mesa, such as modularity, strong type-checking, and the use of libraries with separate interfaces and implementations.
The Development of Cedar
Following the success of Mesa, Xerox PARC developed a language called Cedar, which was essentially a superset of Mesa. Cedar was designed to extend and refine many of the features introduced by Mesa, including its support for modular programming, exception handling, and concurrency. Cedar would go on to serve as the foundation for much of the software infrastructure at Xerox PARC in the 1980s and early 1990s.
Like Mesa, Cedar was influential in the development of other programming languages and software systems. Many of the principles established by Mesa were further refined and adopted by languages and systems that followed, contributing to the evolution of programming languages in the late 20th century.
Mesaβs Influence on Modula-2 and Java
The design principles of Mesa, particularly in the areas of modularity, type-checking, and system-level programming, had a profound influence on later programming languages. One of the most direct descendants of Mesa was Modula-2, a language designed by Niklaus Wirth in the 1970s. Modula-2 was a successor to Pascal and introduced several features that were directly inspired by Mesa, including modular programming and support for separate compilation. Modula-2 also adopted Mesa’s emphasis on strong type-checking and its approach to managing program dependencies through explicit interface definitions.
Java, the widely used programming language developed by Sun Microsystems in the mid-1990s, also owes much of its design to Mesa. Java borrowed key concepts from Mesa, such as its strong support for modularity and its focus on type safety and error handling. In fact, many of the design choices made by the creators of Java, particularly in terms of libraries and exception handling, can be traced back to innovations introduced in Mesa. This legacy is especially evident in Java’s use of a runtime environment (the Java Virtual Machine, or JVM), which shares some similarities with the type-checking and exception handling mechanisms that were first introduced by Mesa.
Mesa’s Lasting Legacy
While Mesa is no longer in widespread use, its contributions to the field of programming languages are undeniable. Its support for modular programming, type-checking, exception handling, and thread synchronization paved the way for modern programming practices and influenced the design of languages that are still in use today. The concepts and principles introduced by Mesa continue to shape the way software is written, with their impact seen in everything from object-oriented programming to multi-threaded applications.
Mesa’s development at Xerox PARC also had a broader impact on the field of computer science. It was part of a larger movement at PARC to explore new ways of interacting with computers, including the development of the GUI and the invention of the laser printer. The innovations that came out of Xerox PARC, including Mesa, helped set the stage for the personal computer revolution and the subsequent rise of networked computing.
Conclusion
Mesa was a groundbreaking programming language that not only influenced the development of other important languages like Modula-2 and Java but also played a critical role in the advancement of modular programming, exception handling, and thread synchronization. Its innovations, born out of the research at Xerox PARC, were pivotal in shaping modern software engineering practices and contributed significantly to the development of graphical user interfaces and multi-tasking systems. While Mesa may not be as widely known today as some other programming languages, its legacy endures in the technologies and systems that continue to define the computing landscape.