Users and applications
Formal description
Use in data structures
Architectural roots
Making pointers safer
Simulation using an array index
Project partners & contact details
Pascal (programming language)
Pascal is an imperative and procedural programming language, designed by Niklaus Wirth as a small, efficient language intended to encourage good programming practices using structured programming and data structuring. It is named in honor of the French mathematician, philosopher and physicist Blaise Pascal.
Pascal became very successful in the 1970s, notably on the burgeoning minicomputer market. Compilers were also available for many microcomputers as the field emerged in the late 1970s. It was widely used as a teaching language in university-level programming courses in the 1980s, and also used in production settings for writing commercial software during the same period. It was displaced by the C programming language during the late 1980s and early 1990s as UNIX-based systems became popular, and especially with the release of C++.
By this time, a number of problems in ALGOL had been identified, notably the lack of a standardized string system. The group tasked with maintaining the language had begun the ALGOL X process to identify improvements, calling for submissions. Wirth and Tony Hoare submitted a conservative set of modifications to add strings and clean up some of the syntax. These were considered too minor to be worth using as the new standard ALGOL, so Wirth wrote a compiler for the language, which became known as ALGOL W.
One of the early successes for language was the introduction of UCSD Pascal, a version that ran on a custom operating system that could be ported to different platforms. A key platform was the Apple II, where it saw widespread use. This led to the use of Pascal becoming the primary high-level language used for development in the Apple Lisa, and later, the Macintosh. Parts of the original Macintosh operating system were hand-translated into Motorola 68000 assembly language from the Pascal sources.
During work on the Lisa, Larry Tesler began corresponding with Wirth on the idea of adding object oriented extensions to the language. This led initially to Clascal, introduced in 1983. As the Lisa program faded and was replaced by the Mac, a further version known as Object Pascal was created. This was introduced on the Macintosh in 1985 as part of the MacApp application framework, and became Apple's primary development language into the early 1990s.
Pascal, like many programming languages of today (but unlike most languages in the C family), allows nested procedure definitions to any level of depth, and also allows most kinds of definitions and declarations inside subroutines (procedures and functions). This enables a very simple and coherent syntax where a complete program is syntactically nearly identical to a single procedure or function (except for the heading, which has one of these three keywords).
The first successful port of the CDC Pascal compiler to another mainframe was completed by Welsh and Quinn at the Queen's University of Belfast (QUB) in 1972. The target was the ICL 1900 series. This compiler, in turn, was the parent of the Pascal compiler for the Information Computer Systems (ICS) Multum minicomputer. The Multum port was developed with a view to using Pascal as a systems programming language by Findlay, Cupples, Cavouras and Davis, working at the Department of Computing Science in Glasgow University. It is thought that Multum Pascal, which was completed in the summer of 1973, may have been the first 16-bit implementation.
In 1986, Anders ported Turbo Pascal to the Macintosh and incorporated Apple's Object Pascal extensions into Turbo Pascal. These extensions were then added back into the PC version of Turbo Pascal for version 5.5. At the same time Microsoft also implemented the Object Pascal compiler. Turbo Pascal 5.5 had a large influence on the Pascal community, which began concentrating mainly on the IBM PC in the late 1980s. Many PC hobbyists in search of a structured replacement for BASIC used this product. It also began to be adopted by professional developers. Around the same time a number of concepts were imported from C to let Pascal programmers use the C-based API of Microsoft Windows directly. These extensions included null-terminated strings, pointer arithmetic, function pointers, an address-of operator and unsafe typecasts.
IP Pascal was an implementation of the Pascal programming language using Micropolis DOS, but was moved rapidly to CP/M-80 running on the Z80. It was moved to the 80386 machine types in 1994, and exists today as Windows/XP and Linux implementations. In 2008, the system was brought up to a new level and the resulting language termed "Pascaline" (after Pascal's calculator). It includes objects, namespace controls, dynamic arrays, along with many other extensions, and generally features the same functionality and type protection as C#. It is the only such implementation that is also compatible with the original Pascal implementation, which is standardized as ISO 7185.
The ISO 7185 was stated to be a clarification of Wirth's 1974 language as detailed by the User Manual and Report [Jensen and Wirth], but was also notable for adding "Conformant Array Parameters" as a level 1 to the standard, level 0 being Pascal without conformant arrays. This addition was made at the request of C. A. R. Hoare, and with the approval of Niklaus Wirth. The precipitating cause was that Hoare wanted to create a Pascal version of the (NAG) Numerical Algorithms Library, which had originally been written in FORTRAN, and found that it was not possible to do so without an extension that would allow array parameters of varying size. Similar considerations motivated the inclusion in ISO 7185 of the facility to specify the parameter types of procedural and functional parameters.