Mesa
is a
programming language
A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language.
The description of a programming ...
developed in the late 1970s at the
Xerox Palo Alto Research Center
Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and digital document products and services in more than 160 countries. Xerox is headquartered in Norwalk, Connecticut (having moved from Stamf ...
in
Palo Alto, California
Palo Alto (; Spanish language, Spanish for "tall stick") is a charter city in the northwestern corner of Santa Clara County, California, United States, in the San Francisco Bay Area, named after a Sequoia sempervirens, coastal redwood tree kno ...
,
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
. 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. 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
Thread may refer to:
Objects
* Thread (yarn), a kind of thin yarn used for sewing
** Thread (unit of measurement), a cotton yarn measure
* Screw thread, a helical ridge on a cylindrical fastener
Arts and entertainment
* ''Thread'' (film), 2016 ...
synchronization
Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...
, and
incremental compilation.
Mesa was developed on the
Xerox Alto, one of the first
personal computer
A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...
s with a
graphical user interface
The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...
, however, most of the Alto's system software was written in
BCPL
BCPL ("Basic Combined Programming Language") is a procedural, imperative, and structured programming language. Originally intended for writing compilers for other languages, BCPL is no longer in common use. However, its influence is still ...
. 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.
Mesa and Cedar had a major influence on the design of other important languages, such as
Modula-2
Modula-2 is a structured, procedural programming language developed between 1977 and 1985/8 by Niklaus Wirth at ETH Zurich. It was created as the language for the operating system and application software of the Lilith personal workstation. It w ...
and
Java
Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...
, and was an important vehicle for the development and dissemination of the fundamentals of
GUI
The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...
s, networked environments, and the other advances
Xerox
Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and electronic document, digital document products and services in more than 160 countries. Xerox is headquartered in Norwalk, Connecticut (ha ...
contributed to the field of
computer science
Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...
.
History
Mesa was originally designed in the Computer Systems Laboratory (CSL), a branch of the Xerox Palo Alto Research Center, for the
Alto
The musical term alto, meaning "high" in Italian (Latin: ''altus''), historically refers to the contrapuntal part higher than the tenor and its associated vocal range. In 4-part voice leading alto is the second-highest part, sung in choruses by ...
, 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 The Xerox Development Environment was one of the first Integrated development environments (IDEs). It was first implemented on the Xerox Alto in 1977.
See also
* BCPL
* Mesa (programming language)
External links
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
Hack may refer to:
Arts, entertainment, and media Games
* ''Hack'' (Unix video game), a 1984 roguelike video game
* ''.hack'' (video game series), a series of video games by the multimedia franchise ''.hack''
Music
* ''Hack'' (album), a 199 ...
", 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+
Modula-2+ is a programming language descended from the Modula-2 language. It was developed at DEC Systems Research Center (SRC) and Acorn Computers Ltd Research Centre in Palo Alto, California. Modula-2+ is Modula-2 with exceptions and threads. ...
, and later of
Modula-3.
Main features
Semantics
Mesa was a
strongly typed programming language
In computer programming, one of the many ways that programming languages are colloquially classified is whether the language's type system makes it strongly typed or weakly typed (loosely typed). However, there is no precise technical definition o ...
with type-checking across module boundaries, but with enough flexibility in its type system that heap allocators could be written in Mesa.
Due to its strict separation between interface and implementation, Mesa allows true incremental compilation and encourages
architecture
Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing building ...
- and
platform-independent programming. They also simplified source-level
debugging
In computer programming and software development, debugging is the process of finding and resolving '' bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems.
Debugging tactics can involve in ...
, including remote debugging via the
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
.
Mesa had rich
exception handling facilities, with four types of exceptions. It had support for thread synchronization via monitors. Mesa was the first language to implement monitor BROADCAST, a concept introduced by the Pilot operating system.
Syntax
Mesa has an "imperative" and "algebraic"
syntax
In linguistics, syntax () is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure ( constituency) ...
, based on
ALGOL and
Pascal
Pascal, Pascal's or PASCAL may refer to:
People and fictional characters
* Pascal (given name), including a list of people with the name
* Pascal (surname), including a list of people and fictional characters with the name
** Blaise Pascal, Fren ...
rather than on BCPL or
C; for instance,
compound commands are indicated by the and keywords rather than
brace
Brace(s) or bracing may refer to:
Medical
* Orthopaedic brace, a device used to restrict or assist body movement
** Back brace, a device limiting motion of the spine
*** Milwaukee brace, a kind of back brace used in the treatment of spinal cur ...
s. In Mesa, all keywords are written in uppercase.
Due to PARC's using the 1963 variant of
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
rather than the more common 1967 variant, the Alto's character set included a left-pointing arrow (←) rather than an underscore. The result of this is that Alto programmers (including those using Mesa, Smalltalk etc.) conventionally used
camelCase
Camel case (sometimes stylized as camelCase or CamelCase, also known as camel caps or more formally as medial capitals) is the practice of writing phrases without spaces or punctuation. The format indicates the separation of words with a single ...
for compound identifiers, a practice which was incorporated in PARC's standard programming style. On the other hand, the availability of the left-pointing arrow allowed them to use it for the assignment operator, as it originally had been in ALGOL.
When the Mesa designers wanted to implement an exception facility, they hired a recent M.Sc. graduate from Colorado who had written his thesis on exception handling facilities in algorithmic languages. This led to the richest exception facility for its time, with primitives , , , , , and . As the language did not have type-safe checks to verify full coverage for signal handling, uncaught exceptions were a common cause of bugs in released software.
Cedar
Mesa was the precursor to the programming language Cedar.
Cedar's main additions were
garbage collection
Waste collection is a part of the process of waste management. It is the transfer of solid waste from the point of use and disposal to the point of treatment or landfill. Waste collection also includes the curbside collection of recyclable m ...
,
dynamic types, better string support through
ropes, a limited form of
type parameterization, and special syntax for identifying the
type-safe parts of multi-module software packages, to ensure deterministic execution and prevent
memory leaks.
Descendants
*The
United States Department of Defense
The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national secu ...
approached Xerox to use Mesa for its "IronMan" programming language (see
Steelman language requirements
The Steelman language requirements were a set of requirements which a high-level general-purpose programming language should meet, created by the United States Department of Defense in ''The Department of Defense Common High Order Language program' ...
), but Xerox declined due to conflicting goals. Xerox PARC employees argued that Mesa was a proprietary advantage that made Xerox software engineers more productive than engineers at other companies. The Department of Defense instead eventually chose and developed the
Ada programming language from the candidates.
*The original Star Desktop evolved into the ViewPoint Desktop and later became
GlobalView which was ported to various Unix platforms, such as
SunOS Unix and
AIX
Aix or AIX may refer to:
Computing
* AIX, a line of IBM computer operating systems
*An Alternate Index, for a Virtual Storage Access Method Key Sequenced Data Set
*Athens Internet Exchange, a European Internet exchange point
Places Belgium
...
. A Mesa to
C compiler was written and the resulting code compiled for the target platform. This was a workable solution but made it nearly impossible to develop on the Unix machines since the power of the Mesa compiler and associated tool chain was lost using this approach. There was some commercial success on Sun SPARC workstations in the publishing world, but this approach resulted in isolating the product to narrow market opportunities.
*In 1976, during a sabbatical at Xerox PARC,
Niklaus Wirth became acquainted with Mesa, which had a major influence in the design of his
Modula-2
Modula-2 is a structured, procedural programming language developed between 1977 and 1985/8 by Niklaus Wirth at ETH Zurich. It was created as the language for the operating system and application software of the Lilith personal workstation. It w ...
language.
*
Java
Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...
explicitly refers to Mesa as a predecessor.
See also
*
History of the graphical user interface
The history of the graphical user interface, understood as the use of graphic icon (computing), icons and a pointing device to control a computer, covers a five-decade span of incremental refinements, built on some constant core principles. Se ...
References
External links
Mesa Programming Language Manual, Version 5 (1979)at bitsavers.org
Other Mesa documentsat bitsavers.org
Don Gillies, Xerox SDD/ISD Employee, 1984–86.
*
{{DEFAULTSORT:Mesa (Programming Language)
Xerox
Procedural programming languages
Concurrent programming languages
Programming languages created in 1976
Statically typed programming languages
Systems programming languages