|
Mesa is an innovative programming language (superseded by the Cedar language) developed in the late 1970s at the Xerox Palo Alto Research Center in Palo Alto, California, United States. The language name was a pun based upon the programming language catchphrases of the time, because Mesa is a "high level" programming language. Mesa is an ALGOL-like language with strong support for modular programming. Every library module has at least two source files: a ''definitions'' file specifying the library's interface plus one or more ''program'' files specifying the implementation of the procedures in the interface.〔Mesa Language Manual, chapter 7. (The Manual uses the term ''module'' to mean a source file.)〕 To use a library, a program or higher-level library must "import" the definitions. The Mesa compiler type-checks all uses of imported entities; this combination of separate compilation with type-checking was unusual at the time. Mesa introduced several other innovations in language design and implementation, notably in the handling of software exceptions, thread synchronization, incremental compilation, and more. Mesa was developed on the Xerox Alto, one of the first personal computers with a graphical user interface, however most of the Alto's system software was written in BCPL. Mesa was the system programming language of the later Xerox Star workstations, and for the GlobalView desktop environment. Xerox PARC later developed Cedar, which was a superset of Mesa, with a number of additions including garbage collection, better string support, called Ropes, and later a native compiler for Sun SPARC workstations. Most importantly, Cedar contained a type-safe subset and the compiler had a subset-checking mode to ensure deterministic execution and no memory leaks from conformant Cedar code. Mesa had a major influence on the design of other important languages, such as Modula-2 and Java, and was an important vehicle for the development and dissemination of the fundamentals of GUIs, networked environments, and the other advances Xerox contributed to the field of computer science. ==History== Mesa was originally designed in the Computer Systems Laboratory (CSL), a branch of the Xerox Palo Alto Research Center, for the Alto, an experimental micro-coded workstation. Initially its spread was confined to PARC and a few universities to which Xerox had donated some Altos. Mesa was later adopted as the systems programming language for Xerox's commercial workstations such as the Xerox 8010 (Xerox Star, Dandelion) and Xerox 6085 (Daybreak), in particular for the Pilot operating system. A secondary development environment, called the Xerox Development Environment (XDE) allowed developers to debug both the operating system Pilot as well as ViewPoint GUI applications using a world swap mechanism. This allowed the entire "state" of the world to be swapped out, and allowed low level system crashes which paralyzed the whole system to be debugged. This technique did not scale very well to large application images (several megabytes), and so the Pilot/Mesa world in later releases moved away from the world swap view when the micro-coded machines were phased out in favor of SPARC workstations and Intel PCs running a Mesa PrincOps emulator for the basic hardware instruction set. Mesa was compiled into a stack-machine language, purportedly with the highest code density ever achieved (roughly 4 bytes per high-level language statement). This was touted in a 1981 paper where implementors from the Xerox Systems Development Department (then, the development arm of PARC), tuned up the instruction set and published a paper on the resultant code density. Mesa was taught via the Mesa Programming Course that took people through the wide range of technology Xerox had available at the time and ended with the programmer writing a "hack", a workable program designed to be useful. An actual example of such a hack is the BWSMagnifier, which was written in 1988 and allowed people to magnify sections of the workstation screen as defined by a resizable window and a changeable magnification factor. Trained Mesa programmers from Xerox were well versed in the fundamental of GUIs, networking, exceptions, and multi-threaded programming, almost a decade before they became standard tools of the trade. Within Xerox, Mesa was eventually superseded by the Cedar programming language. Many Mesa programmers and developers left Xerox in 1985; some of them went to DEC Systems Research Center where they used their experience with Mesa in the design of Modula-2+, and later of Modula-3. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mesa (programming language)」の詳細全文を読む スポンサード リンク
|