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Pascal (programming language)

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Pascal is an imperative and procedural programming language. It was designed to be small and efficient. The goal was to encourage good programming practices. These practices include structured programming and data structuring. Niklaus Wirth designed the language to help people write organized code. He wanted to bridge the gap between scientific and commercial programming. This gap existed between languages like Fortran and COBOL. Pascal is named after the French mathematician and physicist Blaise Pascal.

The language works through several specific mechanisms. It is built on the pattern of the ALGOL 60 language. Pascal uses scalars and arrays to handle basic data. It also allows users to define complex data types. These types help build dynamic and recursive data structures. Examples of these structures include lists, trees, and graphs. A key feature is strong typing on all objects. This means one data type cannot be interpreted as another. This happens unless the programmer uses explicit conversions.

Pascal has unique structural rules compared to other languages. Unlike the C language, Pascal allows nested procedure definitions. These can be nested to any depth. It also allows most definitions and declarations inside subroutines. Subroutines include both procedures and functions. This makes a program look syntactically similar to a single function. This structure is similar to the block structure of ALGOL 60. However, Pascal restricts arbitrary block statements. It limits them to just procedures and functions.

The history of Pascal began with efforts to improve ALGOL. In the 1960s, many designers worked on the ALGOL 60 language. Wirth worked on the Euler language starting in 1962. Euler was based on ALGOL syntax but was not a derivative. Wirth also worked on the ALGOL X process. He proposed a version called ALGOL W. The ALGOL X process became too complex and stalled. Wirth abandoned that process in 1968. He improved ALGOL W and released it as Pascal in 1970.

Pascal saw great success in the 1970s and 1980s. It was very popular in the burgeoning minicomputer market. In the 1980s, it was a common teaching language in universities. It was also used to write commercial software. One major success was UCSD Pascal. This version ran on a custom operating system. It could be ported to different platforms. This version was especially important for the Apple II. This version later became Apple Pascal.

Different versions and dialects of Pascal emerged over time. In 1985, a derivative called Object Pascal was developed. This was designed for object-oriented programming. It was used by Apple for the Lisa and Macintosh. Later, it became the Delphi system for Microsoft Windows. Another important version is the ISO 7185 standard. This was published in 1983. It was used on mainframes and IBM-PCs. Wirth also developed Modula-2 and Oberon from Pascal concepts.

Many famous software applications were built using Pascal. The TeX typesetting system was written in WEB. WEB was based on PDP-10 Pascal. Adobe Photoshop was written in Macintosh Programmer's Workshop Pascal. Other major applications include Skype and Total Commander. These were built using Delphi. Even the Apollo Computer used Pascal for its operating systems starting in 1980. While C displaced Pascal in the 1990s, Pascal remains influential. Modern versions like Free Pascal and Lazarus still exist today.

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