Pascal programming language

From Exampleproblems

Pascal is an imperative computer programming language, developed in 1970 by Niklaus Wirth as a language particularly suitable for structured programming.

Pascal is based on the ALGOL programming language and named in honor of mathematician and philosopher Blaise Pascal. Wirth also developed Modula-2 and Oberon, languages similar to Pascal. Oberon also supports object-oriented programming.

Initially, Pascal was a language intended to teach students structured programming, and generations of students have "cut their teeth" on Pascal as an introductory language in undergraduate courses. Variants of Pascal are still widely used today, both in education and software development.

Much of the original Macintosh operating system was written in Pascal. The popular typesetting system TeX is written in a language named WEB for which Donald Knuth borrowed heavily from Pascal.

1 Language
2 Implementations
3 Standards
4 Divisions
5 Publicly available compilers
6 Past criticism
7 Further reading
8 See also
9 External links

Language

All Pascal programs start with the "Program" keyword, an optional list of external file descriptors and then a block of code is indicated with the "Begin" and "End" keywords. Semicolons separate statements, and the full stop ends the program (or unit). Letter case is ignored in Pascal source.

program HelloWorld(output);
 
begin

    writeln('Hello, World!')

end.

Pascal, in its original form, is a purely procedural language with the standard array of if, while, for, and related constructs.

Pascal is a structured programming language, meaning that the flow of control is structured into standard statements, ideally without 'go to' commands.

while a <> b do WriteLn('Waiting');
 
if a > b then
    writeln('Condition met')
else
    writeln('Condition false');
 
for i := 1 to 10 do writeln('Iteration: ', i:1);
 
repeat a := a + 1 until a = 10;

Pascal structures programs into procedures and functions.

program mine(output);
 
    procedure print(var i: integer);
 
        function next(i: integer): integer;

        begin

            next := i + 1

        end;
 
    begin

        writeln('The total is: ', i);
        i := next(i)

    end;
 
begin

    i := 1;
    while i <= 10 do print(i)

end.

Procedures and functions can nest to any depth, and the 'program' construct is the logical outermost block.

Each block can have its own declarations of goto labels, constants, types, variables, and other procedures and functions, which must all be in that order.

Pascal has integer, character and boolean as the simple types, plus enumerations, a new type introduced with Pascal.

program myprog;
 
var
    a: integer;
    b: char;
    c: boolean;
    d: (one, two, three, four, five);

A "subrange" of any of the above types can be made.

var
    x: 1..10;
    y: 'a'..'z';
    z: two..four;

Types can be built from other types by the type declaration.

program myotherprog;
 
type
    x = integer;
    y = x;
...

Further, complex types can be constructed from simple types:

type 
    a = array [1..10] of integer;
    b = record
            a: integer;
            b: char
        end;
    c = file of a;

Strings are packed arrays that start with an integer index of 1.

Also, Pascal supports the use of pointers:

type 
     a = ^b;
     b = record
            a: integer;
            b: char;
            c: a
         end;
var
     pb : a

Here the variable pb is a pointer to the data type b, a record. To create a new record and assign the values 10 and A to the fields a and b in the record, the commands would be;

  new(pb);
  pb^.a := 10;
  pb^.b := 'A';
  pb^.c := nil;
...

Linked lists can be created by including a pointer type field (c) in the record.

Implementations

The first Pascal compiler was designed in Zurich for the CDC 6000 computer family, and it became operational in 1970.

The first Pascal compiler written in North America was constructed at the University of Illinois under Donald B. Gillies for the PDP-11 and generated native machine code.

In order to rapidly propagate the language, a compiler "porting kit" was created in Zurich that included a compiler for a "virtual" machine code (or more properly an intermediate code), and a simulator for that same code. This became the P-system. Although this system was intended to enable true machine code compilers to be created, at least one system, the notable UCSD implementation, utilized it to create an interpretive system UCSD p-System. The P-system compilers were termed P1-P4, with P1 being the first version, and P4 being the last.

IP Pascal was an implementation of the Pascal programming language using Micropolis DOS, but was moved rapidly to CP/M running on the Z80.

In the early 1980s, UCSD Pascal was ported to the Apple II and Apple III computers to provide a structured alternative to the BASIC interpreters that came with the machines.

In the 1980s Anders Hejlsberg wrote the Blue Label Pascal compiler for the Nascom-2. Later he went to work for Borland and rewrote his compiler to become Turbo Pascal for the IBM PC. This new compiler sold for $49.95, which was much less than the price Hejlsberg originally asked for the Blue Label Pascal compiler.

The inexpensive Borland compiler had a large influence on the Pascal community that 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.

Super Pascal was a variant which added non-numeric labels, a return statement and expressions as names of types.

With Turbo Pascal version 5.5 Borland added object orientation to Pascal.

However, Borland later decided it wanted more elaborate object-oriented features, and started over in Delphi using the Object Pascal draft standard proposed by Apple as a basis. (This Apple draft is still not a formal standard.) Borland also called this Object Pascal in the first Delphi versions, but changed the name to Delphi programming language in later versions. The main additions compared to the older OOP extensions were a reference-based object model, virtual constructors and destructors, and properties. There are several other compilers implementing this dialect: see Delphi programming language.

Turbo Pascal, and other derivatives with units or module concepts are modular languages. Turbo Pascal copied these concepts from either a draft of the Extended Pascal standard or Pascal's successor Modula-2. However, it does not provide a nested module concept or qualified import and export of specific symbols.

Standards

In 1983, the language was standardized, in the international standard ISO/IEC 7185, as well as several local country specific standards, including the American ANSI/IEEE770X3.97-1983. In 1990, an extended Pascal standard was created as ISO/IEC 10206.

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.

Note that Niklaus Wirth himself referred to the 1974 language as "the Standard", for example, to differentiate it from the machine specific features of the CDC 6000 compiler.

On the large machines (mainframes and minicomputers) Pascal originated on, the standards were generally followed. On the IBM-PC, they were not. On IBM-PCs, the Borland standards Turbo Pascal and Delphi have the greatest number of users. Thus, it is typically important to understand whether a particular implementation corresponds to the original Pascal language, or a Borland dialect of it.

Divisions

Niklaus Wirth's Zurich version of Pascal was issued outside of ETH in two basic forms, the CDC 6000 compiler source, and a porting kit called Pascal-P system. The Pascal-P compiler left several features of the full language out. For example, procedures and functions as parameters, undiscriminated variant records, packing, dispose, interprocedural gotos and other features of the full compiler were left off.

UCSD Pascal, under professor Kenneth Bowles, used the Pascal-P2 kit, and consequentially had several of the same differences with the full Zurich Pascal compiler as the Pascal-P compiler did. UCSD Pascal later was adopted as Apple Pascal, and continued through several versions there.

Borland's Turbo Pascal, written by Anders Hejlsberg was written in assembly language independent of UCSD or the Zurich compilers. But it adopted much of the same subset as the UCSD compiler, probably because at that time, UCSD was the most common Pascal system running on Microprocessors.

Publicly available compilers

Several Pascal compilers are available for the use of general public:

P4 compiler, the basis for many subsequent Pascal-implemented-in-Pascal compilers, including the UCSD p-System.
Free Pascal is written in Pascal (so that it compiles itself), and is aimed at providing a convenient and powerful compiler, able both to compile legacy applications and to be the means of develop new ones. Also distributed freely under the GNU GPL. It can mix Turbo Pascal with Delphi code, and supports a lot of platforms and operating systems.
Turbo Pascal was the dominant Pascal compiler for PCs during the 80s and early 90s, popular both because of its powerful extensions and extremely low compilation times. Currently, older versions of Turbo Pascal (up to 5.5) are available for free download from Borland's site (registration required).
Chrome is a next generation Object Pascal language for the .NET and Mono Platforms implemented by RemObjects Software.
GNU Pascal Compiler (GPC) is the Pascal compiler of the GNU Compiler Collection (GCC). The compiler itself is written in C, the runtime library mostly in Pascal. Distributed freely under the GNU General Public License, it runs on many platforms and operating systems. It supports the ANSI/ISO standard languages and the Borland/Turbo Pascal language largely. Support for Borland Delphi and other language variations is quite limited yet.
Delphi is Borland's flagship RAD (Rapid Application Development) product. It uses the Delphi programming language, descended from Pascal, to create applications for the windows platform. The latest version also supports compiling to the .NET platform
Kylix is Borland's newest reiteration of the Pascal branch of their products. It is the descendant of Delphi, with support for the Linux operating system and an improved object library. The compiler and the IDE are available now for non-commercial use. The compiler (but not the library or the IDE) is supposed to become Open Source software some time soon.
Dr. Pascal is an interpreter that runs Standard Pascal. Notable are the "visible execution" mode that shows a running program and its variables, and the extensive runtime error checking. Runs programs but does not produce a separate executable binary. Runs on MS-DOS, Windows in DOS window, and old Macintosh.
Virtual Pascal was created by Vitaly Miryanov in 1995 as a native OS/2 compiler compatible with Borland Pascal syntax. Then it had been commercially developed by fPrint, adding Win32 support, and in 2000 it became freeware. Today it can compile for Win32, OS/2 and Linux, and is mostly compatible with Borland Pascal and Delphi.
IP Pascal Originally a Z80/CP/M Pascal that was ported and recoded for Intel 80386/PC, IP Pascal has a built-in portability library that is custom tailored to the Pascal language. For example, a standard text output application from 1970's original Pascal can be recompiled to work in a window and even have graphical constructs added. IP Pascal supports the ISO 7185 standard and upgrades the language logically. For example, original Pascal "padded right" strings are supported and integrated upwards seamlessly into dynamic strings. Standard Pascal static arrays are enhanced with dynamic arrays which are fully downward compatible with static arrays, etc.
Pocket Studio is a Pascal subset compiler/RAD targeting Palm / MC68xxx with some own extensions to assist interfacing with the Palm OS API.
Lazarus is a cross platform Visual RAD IDE. Lazarus uses Free Pascal complier.

A very extensive list can be found on Pascaland. The site is in French, but it is basically a list with URLs to compilers, so that does not matter. You may also check out Pascal Central, a Mac centric Pascal info and advocacy site with rich collection of article archives, plus links to many compilers and tutorials.

Past criticism

While very popular (although more so in the 1980s and early 1990s than at the time of writing), early versions of Pascal have been widely criticised for being unsuitable for "serious" use outside of teaching. Brian Kernighan, famed populariser of the C programming language, outlined his most notable criticisms of Pascal as early as 1981, in his paper Why Pascal Is Not My Favorite Programming Language. On the other hand, many major development efforts in the 1980s, such as for the Apple Lisa and Macintosh, heavily depended on Pascal (to the point where the C interface for the Mac OS API had to deal in Pascal data types). In the decades since then, Pascal has continued to evolve and most of Kernighan's points do not apply to current implementations. Unfortunately, just as Kernighan predicted in his article, most of the extensions to fix these issues were incompatible from compiler to compiler. In the last decade, however, the varieties seem to have condensed into two categories, ISO or Borland like, a better eventual outcome than Kernighan foresaw.

Based on his experience with Pascal Niklaus Wirth developed two more programming languages, Modula-2 and Oberon, which even though much improved did not meet the commercial success of Pascal.

External links

Pascal Central — the one-stop Pascal resource site
Real Programmers Don't Use Pascal — a joke about why "real programmers" don't use Pascal
Standard Pascal — Resources and history of original, standard Pascal
Pascal User's Group Newsletters — An early Pascal history resource that contains many letters from Wirth and others concerning Pascal.
Pascal and its Successors — An article by Niklaus Wirth about the development of Pascal, Modula-2 and Oberon

Template:Major programming languages small be:Pascal bg:Pascal cs:Pascal (programovací jazyk) da:Pascal (programmeringssprog) de:Pascal (Programmiersprache) et:Pascal es:Lenguaje de programación Pascal eo:Pascal fr:Pascal (langage) gl:Linguaxe Pascal ko:파스칼 프로그래밍 언어 id:Pascal (bahasa pemrograman) it:Pascal (linguaggio) he:Pascal lt:Pascal hu:Pascal programozási nyelv mk:Паскал nl:Pascal (programmeertaal) ja:Pascal pl:Pascal (język programowania) pt:Pascal (linguagem de programação) ro:Limbajul Pascal ru:Паскаль (язык программирования) sk:Pascal (programovací jazyk) sl:Programski jezik pascal fi:Pascal-ohjelmointikieli sv:Pascal (programspråk) tl:Pascal (programming language) th:ภาษาปาสกาล vi:Pascal (ngôn ngữ lập trình) tr:Pascal programlama dili uk:Мова програмування Pascal zh:Pascal

Retrieved from "http://www.exampleproblems.com/wiki/index.php/Pascal_programming_language"

Pascal programming language

From Exampleproblems

Contents

Language

Implementations

Standards

Divisions

Publicly available compilers

Past criticism

Further reading

See also

External links

Views

Personal tools

Example problems .com

Search

Toolbox