Топики по ангийскому языку / языки программирования

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Algol

The language Component Pascal is the culmination of several decades of research. It is the youngest member of the Algol family of languages. Algol, defined in 1960, was the first high-level language with a readable, structured, and systematically defined syntax. While successful as a notation for mathematical algorithms, it lacked important data types, such as pointers or characters.

Pascal

In the late sixties, several proposals for an evolutionary successor to Algol were developed. The most successful one was Pascal, defined in 1970 by Prof. Niklaus Wirth at ETH Zьrich, the Swiss Federal Institute of Technology. Besides cleaning up or leaving out some of Algol's more obscure features, Pascal added the capability to define new data types out of simpler existing ones. Pascal also supported dynamic data structures; i.e., data structures which can grow and shrink while a program is running.

Pascal received a big boost when ETH released a Pascal compiler that produced a simple intermediate code for a virtual machine (P-code), instead of true native code for a particular machine. This simplified porting Pascal to other processor architectures considerably, because only a new P-code interpreter needed be written for this purpose, not a whole new compiler. One of these projects had been undertaken at the University of California, San Diego. Remarkably, this implementation (UCSD Pascal) didn't require a large and expensive mainframe computer, it ran on the then new Apple II personal computers. This gave Pascal a second important boost. The third one came when Borland released TurboPascal, a fast and inexpensive compiler, and integrated development environment for the IBM PC. Later, Borland revived its version of Pascal when it introduced the rapid application development environment Delphi.

Pascal has greatly influenced the design and evolution of many other languages, from Ada to Visual Basic.

Modula-2

In the mid-seventies, inspired by a sabbatical at the Xerox Palo Alto Research Center PARC, Wirth started a project to develop a new workstation computer. This workstation should be completely programmable in a high-level language, thus the language had to provide direct access to the underlying hardware. Furthermore, it had to support team programming and modern software engineering principles, such as abstract data types. These requirements led to the programming language Modula-2 (1979).

Modula-2 retained the successful features of Pascal, and added a module system as well as a controlled way to circumvent the language's type system when doing low-level programming; e.g., when implementing device drivers. Modules could be added to the operating system at run-time. In fact, the whole operating system consisted of a collection of modules, without a distinguished kernel or similar artefact. Modules could be compiled and loaded separately, with complete type and version checking of their interfaces.

Modula-2 has made inroads in particular into safety-critical areas, such as traffic control systems.

Simula, Smalltalk, and Cedar

Wirth's interest remained with desktop computers, however, and again an important impulse came from Xerox PARC. PARC was the place where the workstation, the laser printer, the local area network, the bitmap display, and many other enabling technologies have been invented. Also, PARC adopted and made popular several older and barely known technologies, like the mouse, interactive graphics, and object-oriented programming. The latter concept, if not the term, was first applied to a high-level language in Simula (1966), another member of the Algol language family. As its name suggests, Simula used object-orientation primarily for simulation purposes. Xerox PARC's Smalltalk language (1983), however, used it for about anything. The Smalltalk project broke new ground also in user interface design: the graphical user interface (GUI) as we know it today was developed for the Smalltalk system.

At PARC, these ideas influenced other projects, e.g., the Cedar language, a Pascal-style language. Like Smalltalk and later Oberon, Cedar was not only the name of a language but also of an operating system. The Cedar operating system was impressive and powerful, but also complex and unstable.