pascal progammer language

Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.
A derivative known as Object Pascal was designed for object-oriented programming.
Pascal was developed by Niklaus Wirth and based on the ALGOL programming language, named in honor of the French mathematician and philosopher Blaise Pascal.
Prior to his work on Pascal, Wirth had developed Euler and ALGOL W and later went on to develop the Pascal-like languages Modula-2 and Oberon.
Initially, Pascal was largely, but not exclusively, intended to teach students structured programming.[4] A generation of students used Pascal as an introductory language in undergraduate courses. Variants of Pascal have also frequently been used for everything from research projects to PC games and embedded systems. Newer Pascal compilers exist which are widely used.[5]
Pascal was the primary high-level language used for development in the Apple Lisa, and in the early years of the Mac. Parts of the original Macintosh operating system were hand-translated into Motorola 68000 assembly language from the Pascal sources. The popular typesetting system TeX by Donald E. Knuth was written in WEB, the original literate programming system, based on DEC PDP-10 Pascal, while an application like Total Commander was written in Delphi (Object Pascal).
Object Pascal is still widely used for developing Windows applications such as Skype.
Pascal, in its original form, is a purely procedural language and includes the traditional array of ALGOL-like control structures with reserved words such as if, then, else, while, for, and so on. However, Pascal also has many data structuring facilities and other abstractions which were not included in the original ALGOL 60, like type definitions, records, pointers, enumerations, and sets. Such constructs were in part inherited or inspired from Simula 67, ALGOL 68, Niklaus Wirth's own ALGOL W and suggestions by C. A. R. Hoare.
Hello world
Pascal programs start with the program keyword with a list of external file descriptors as parameters; then follows the main block bracketed by the begin and end keywords. Semicolons separate statements, and the full stop (i.e., a period) ends the whole program (or unit). Letter case is ignored in Pascal source.
Here is an example of the source code in use for a very simple "Hello world" program:
program HelloWorld(output);
begin
Writeln('Hello world!');
end.

Data types
A type in Pascal, and in several other popular programming languages, defines a variable in such a way that it defines a range of values which the variable is capable of storing, and it also defines a set of operations that are permissible to be performed on variables of that type. The predefined types are:
Data type Type of values which the variable is capable of storing
integer Whole numbers
real Floating point numbers
boolean The value TRUE or FALSE
char A single character from an ordered character set
The range of values allowed for each (except boolean) is implementation defined. Functions are provided for some data conversions. For conversion of real to integer, the following functions are available: round, which round to integer using banker's rounding; trunc, round towards zero.
The programmer has the freedom to define other commonly-used data types (e.g. byte, string, etc.) in terms of the predefined types using Pascal's type declaration facility. e.g.
type
byte = 0..255;
signedbyte = -128..127;
string = packed array [1..255] of char;

Scalar types
Pascal's scalar types are real, integer, character, boolean and enumerations, a new type constructor introduced with Pascal:
type
SomeType = (State1,State2,State3);
var
r: Real;
i: Integer;
c: Char;
b: Boolean;
t: SomeType;
e: (apple, pear, banana, orange, lemon);

Subrange types
Subranges of any ordinal type (any simple type except real) can be made:
var
x: 1..10;
y: 'a'..'z';
z: pear..orange;

Set types
In contrast with other programming languages from its time, Pascal supports a set type:
var
set1: set of 1..10;
set2: set of 'a'..'z';
set3: set of pear..orange;

A set is a fundamental concept for modern mathematics, and they may be used in a many algorithms. Such a feature is useful and may be faster than an equivalent construct in a language that does not support sets. For example, for many Pascal compilers:
if i in [5..10] then
...

executes faster than:
if (i>4) and (i<11) then ... Sets of non-contiguous values can be particularly useful, in terms of both performance and readability: if i in [0..3, 7, 9, 12..15] then ... For these examples, which involve sets over small domains, the improved performance is usually achieved by the compiler representing set variables as bitmasks. The set operators can then be implemented efficiently as bitwise machine code operations. Type declarations Types can be defined from other types using type declarations: type x = Integer; y = x; ... Further, complex types can be constructed from simple types: type a = Array [1..10] of Integer; b = record x: Integer; y: Char end; c = File of a; File type As shown in the example above, Pascal files are sequences of components. Every file has a buffer variable which is denoted by f^. The procedures get (for reading) and put (for writing) move the buffer variable to the next element. Read is introduced such that read(f, x) is the same as x:=f^; get(f);. Write is introduced such that write(f, x) is the same as f^ := x; put(f); The type text is predefined as file of char. While the buffer variable could be used for inspecting the next character to be used (check for a digit before reading an integer), this leads to serious problems with interactive programs in early implementations, but was solved later with the "lazy I/O" concept. In Jensen & Wirth Pascal, strings are represented as packed arrays of chars; they therefore have fixed length and are usually space-padded. Some dialects have a custom string type. Pointer types Pascal supports the use of pointers: type Nodeptr = ^Node; Node = record a: Integer; b: Char; c: Nodeptr end; var ptoNode: Nodeptr; pInt : ^Integer; Here the variable ptoNode is a pointer to the data type Node, a record. Pointers can be used before they are declared. This is a forward declaration, an exception to the rule that things must be declared before they are used. To create a new record and assign the value 10 and character A to the fields a and b in the record, and to initialise the pointer c to nil, the commands would be: new(ptoNode); ... ptoNode^.a := 10; ptoNode^.b := 'A'; ptoNode^.c := nil; ... This could also be done using the with statement, as follows new(ptoNode); ... with ptoNode^ do begin a := 10; b := 'A'; c := nil end; ... Inside of the scope of the with statement, a and b refer to the subfields of the record pointer ptoNode and not to the record Node or the pointer type Nodeptr. Linked lists, stacks and queues can be created by including a pointer type field (c) in the record (see also nil). Unlike many languages that feature pointers, Pascal only allows pointers to reference dynamically created variables that are anonymous, and does not allow them to reference standard static or local variables. Pointers also must have an associated type, and a pointer to one type is not compatible with a pointer to another type (e.g. a pointer to a char is not compatible with a pointer to an integer). This helps eliminate the type security issues inherent with other pointer implementations, particularly those used for PL/I or C. It also removes some risks caused by dangling pointers, but the ability to dynamically let go of referenced space by using the dispose function (which has the same effect as the free library function found in C) means that the risk of dangling pointers has not been entirely eliminated. Control structures Pascal is a structured programming language, meaning that the flow of control is structured into standard statements, ideally without 'goto' commands. while a <> b do writeln('Waiting');

if a > b then
writeln('Condition met')
else
writeln('Condition not met');

for i := 1 to 10 do
writeln('Iteration: ', i:1);

repeat
a := a + 1
until a = 10;

case i of
0: write('zero');
1: write('one');
2: write('two')
end;

Procedures and functions
Pascal structures programs into procedures and functions.
program mine(output);

var i : integer;

procedure print(var j: integer);

function next(k: integer): integer;
begin
next := k + 1
end;

begin
writeln('The total is: ', j);
j := next(j)
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 procedure or function can have its own declarations of goto labels, constants, types, variables, and other procedures and functions, which must all be in that order. This ordering requirement was originally intended to allow efficient single-pass compilation. However, in some dialects (such as Embarcadero Delphi) the strict ordering requirement of declaration sections has been relaxed.
Semicolons as statement separators
Pascal adopted many language syntax features from the ALGOL language, including the use of a semicolon as a statement separator. This is in contrast to other languages, such as PL/I, C etc. which use the semicolon as a statement terminator. As illustrated in the above examples, no semicolon is needed before the end keyword of a record type declaration, a block, or a case statement; before the until keyword of a repeat statement; and before the else keyword of an if statement.
The presence of an extra semicolon was not permitted in early versions of Pascal. However, the addition of ALGOL-like empty statements in the 1973 Revised Report and later changes to the language in ISO 7185:1983 now allow for optional semicolons in most of these cases. The exception is that a semicolon is still not permitted immediately before the else keyword in an if statement.

google adense

Google AdSense is an ad serving application run by Google Inc. Website owners can enroll in this program to enable text, image, and video advertisements on their websites. These advertisements are administered by Google and generate revenue on either a per-click or per-impression basis. Google beta tested a cost-per-action service, but discontinued it in October 2008 in favor of a DoubleClick offering (also owned by Google). In Q1 2011, Google earned US$2.34 billion ($9.36 billion annualized), or 28% of total revenue, through AdSense.
Overview
Google uses its Internet search technology to serve advertisements based on website content, the user's geographical location, and other factors. Those wanting to advertise with Google's targeted advertisement system may enroll through AdWords. AdSense has become a popular method of placing advertising on a website because the advertisements are less intrusive than most banners, and the content of the advertisements is often relevant to the website.
Many websites use AdSense to monetize their content; it is the most popular advertising network. AdSense has been particularly important for delivering advertising revenue to small websites that do not have the resources for developing advertising sales programs and sales people. To fill a website with advertisements that are relevant to the topics discussed, webmasters implement a brief script on the websites' pages. Websites that are content-rich have been very successful with this advertising program, as noted in a number of publisher case studies on the AdSense website.
Some webmasters invest significant effort into maximizing their own AdSense income. They do this in three ways:
They use a wide range of traffic-generating techniques, including but not limited to online advertising.
They build valuable content on their websites that attracts AdSense advertisements, which pay out the most when they are clicked.
They use text content on their websites that encourages visitors to click on advertisements. Note that Google prohibits webmasters from using phrases like "Click on my AdSense ads" to increase click rates. The phrases accepted are "Sponsored Links" and "Advertisements".
The source of all AdSense income is the AdWords program, which in turn has a complex pricing model based on a Vickrey second price auction. AdSense commands an advertiser to submit a sealed bid (i.e., a bid not observable by competitors). Additionally, for any given click received, advertisers only pay one bid increment above the second-highest bid. Google currently shares 68% of revenues generated by AdSense with content network partners.

History
Oingo, Inc., a privately held company located in Los Angeles, was started in 1998 by Gilad Elbaz and Adam Weissman. Oingo developed a proprietary search algorithm that was based on word meanings and built upon an underlying lexicon called WordNet, which was developed over the previous 15 years by researchers at Princeton University, led by George Miller.
Oingo changed its name to Applied Semantics in 2001,which was later acquired by Google in April 2003 for US$102 million.
In 2009, Google AdSense announced that it would now be offering new features, including the ability to "enable multiple networks to display ads".
Types
AdSense for Feeds
In May 2005, Google announced a limited-participation beta version of AdSense for Feeds, a version of AdSense that runs on RSS and Atom feeds that have more than 100 active subscribers. According to the Official Google Blog, "advertisers have their ads placed in the most appropriate feed articles; publishers are paid for their original content; readers see relevant advertising—and in the long run, more quality feeds to choose from."
AdSense for Feeds works by inserting images into a feed. When the image is displayed by a RSS reader or Web browser, Google writes the advertising content into the image that it returns. The advertisement content is chosen based on the content of the feed surrounding the image. When the user clicks the image, he or she is redirected to the advertiser's website in the same way as regular AdSense advertisements.
AdSense for Feeds remained in its beta state until August 15, 2008, when it became available to all AdSense users.
AdSense for search
A companion to the regular AdSense program, AdSense for search, allows website owners to place Google search boxes on their websites. When a user searches the Internet or the website with the search box, Google shares 51% of the advertising revenue it makes from those searches with the website owner.However the publisher is paid only if the advertisements on the page are clicked; AdSense does not pay publishers for mere searches.
AdSense for mobile content
AdSense for mobile content allows publishers to generate earnings from their mobile websites using targeted Google advertisements. Just like AdSense for content, Google matches advertisements to the content of a website — in this case, a mobile website. Instead of traditional JavaScript code, technologies such as PHP, ASP and others are used.
AdSense for domains
Adsense for domains allows advertisements to be placed on domain names that have not been developed. This offers domain name owners a way to monetize domain names that are otherwise dormant. Adsense for domains is currently being offered to some users, with plans to make it available to all in stages.
On December 12, 2008, TechCrunch reported that AdSense for Domains is available for all US publishers.
AdSense for video
AdSense for video allows publishers with video content to generate revenue using ad placements from Google's extensive Advertising network including popular Youtube videos.
XHTML compatibility
As of September 2007, the HTML code for the AdSense search box does not validate as XHTML, and does not follow modern principles of website design because of its use of
non-standard end tags, such as and ,
the attribute checked rather than checked="checked",
presentational attributes other than id, class, or style — for example, bgcolor and align,
a table structure for purely presentational (i.e., non-tabular) purposes,1 and
the font tag.2
1: using a table structure for unintended purposes is strongly discouraged by the W3C, but nevertheless does not cause a document to fail validation — there is currently no algorithmic method of determining whether a table is used "correctly" (for displaying tabular data or for displaying elements, that get proportionally wider or narrower when browser window resizes in width without active client side scripting).2: the font tag is deprecated but does not fail validation in any XHTML standard[citation needed].
Additionally, the AdSense advertisement units use the JavaScript method document.write(), which does not work correctly when rendered with the application/xhtml+xml MIME type. The units also use the iframe HTML tag, which is not validated correctly with the XHTML 1.0 Strict or XHTML 1.0 Transitional DOCTYPEs.
The terms of the AdSense program forbid its affiliates from modifying the code, thus preventing these participants from having valid XHTML websites.
However, a workaround has been found by creating a separate HTML webpage containing only the AdSense advertisement units, and then importing this page into an XHTML webpage with an object tag.This workaround appears to be accepted by Google.
How AdSense works
The webmaster inserts the AdSense JavaScript code into a webpage.
Each time this page is visited, the JavaScript code uses inlined JSON to display content fetched from Google's servers.
For contextual advertisements, Google's servers use a cache of the page to determine a set of high-value keywords. If keywords have been cached already, advertisements are served for those keywords based on the AdWords bidding system. (More details are described in the AdSense patent.)
For site-targeted advertisements, the advertiser chooses the page(s) on which to display advertisements, and pays based on cost per mille (CPM), or the price advertisers choose to pay for every thousand advertisements displayed.
For referrals, Google adds money to the advertiser's account when visitors either download the referred software or subscribe to the referred service. The referral program was retired in August 2008.
Search advertisements are added to the list of results after the visitor performs a search.
Because the JavaScript is sent to the Web browser when the page is requested, it is possible for other website owners to copy the JavaScript code into their own webpages. To protect against this type of fraud, AdSense customers can specify the pages on which advertisements should be shown. AdSense then ignores clicks from pages other than those specified.
Abuse
Some webmasters create websites tailored to lure searchers from Google and other engines onto their AdSense website to make money from clicks. These "zombie" websites often contain nothing but a large amount of interconnected, automated content (e.g., a directory with content from the Open Directory Project, or scraper websites relying on RSS feeds for content). Possibly the most popular form of such "AdSense farms" are splogs (spam blogs), which are centered around known high-paying keywords. Many of these websites use content from other websites, such as Wikipedia, to attract visitors. These and related approaches are considered to be search engine spam and can be reported to Google.[citation needed]
A Made for AdSense (MFA) website or webpage has little or no content, but is filled with advertisements so that users have no choice but to click on advertisements. Such pages were tolerated in the past, but due to complaints, Google now disables such accounts.
There have also been reports of Trojan horses engineered to produce counterfeit Google advertisements that are formatted looking like legitimate ones. The Trojan uploads itself onto an unsuspecting user's computer through a webpage and then replaces the original advertisements with its own set of malicious advertisements.
Criticism
Due to alleged concerns about click fraud, Google AdSense has been criticized by some search engine optimization firms as a large source of what Google calls "invalid clicks", in which one company clicks on a rival's search engine advertisements to drive up the other company's costs.
To help prevent click fraud, AdSense publishers can choose from a number of click-tracking programs.[citation needed] These programs display detailed information about the visitors who click on the AdSense advertisements. Publishers can use this to determine whether or not they have been a victim of click fraud. There are a number of commercial tracking scripts available for purchase.
The payment terms for webmasters have also been criticized. Google withholds payment until an account reaches US$100, but many micro content providers[citation needed] require a long time—years in some cases—to build up this much AdSense revenue. However, Google will pay all earned revenue greater than US$10 when an AdSense account is closed and not disabled.
Many website owners complain that their AdSense accounts have been disabled just before they were supposed to receive their first paycheck from Google. Google claims accounts have been disabled due to click fraud or forbidden content, but have offered no proof of this. An automated email is sent to the publisher's owner which offers no reasoning, or options but a link to file an appeal. In the email, Google states that "Because we have a responsibility to protect our AdWords advertisers from inflated costs due to invalid activity, we've found it necessary to disable your AdSense account. Your outstanding balance and Google's share of the revenue will both be fully refunded back to the affected advertisers." The revenue generated - whether legitimate or not - is taken, and all complaints are deferred.
Google came under fire when the official Google AdSense Blog showcased the French video website Imineo.com. This website violated Google's AdSense Program Policies by displaying AdSense alongside sexually explicit material. Typically, websites displaying AdSense have been banned from showing such content. Some sites have been banned for distributing copyrighted material even when they hold the copyright themselves or are authorized by the copyright holder to distribute the material.
It has been reported that using both AdSense and AdWords may cause a website to pay Google a commission when the website advertises itself.
In some cases, AdSense displays inappropriate or offensive ads. For example, in a news story about a terrorist attack in India, an advert was generated for a (presumably non-existent) educational qualification in terrorism.
AdSense sets tracking cookies that are viewed by some as a threat to privacy. Webmasters that use AdSense must place the appropriate warning in the privacy policy page.

Pascal

Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.
History
Pascal was developed by Niklaus Wirth and based on the ALGOL programming language, named in honor of the French mathematician and philosopher Blaise Pascal.
Prior to his work on Pascal, Wirth had developed Euler and ALGOL W and later went on to develop the Pascal-like languages Modula-2 and Oberon.
Initially, Pascal was largely, but not exclusively, intended to teach students structured programming.^[4] A generation of students used Pascal as an introductory language in undergraduate courses. Variants of Pascal have also frequently been used for everything from research projects to PC games and embedded systems. Newer Pascal compilers exist which are widely used.^[5]
Pascal was the primary high-level language used for development in the Apple Lisa, and in the early years of the Mac. Parts of the original Macintosh operating system were hand-translated into Motorola 68000 assembly language from the Pascal sources. The popular typesetting system TeX by Donald E. Knuth was written in WEB, the original literate programming system, based on DEC PDP-10 Pascal, while an application like Total Commander was written in Delphi (Object Pascal).
Brief description
Wirth's intention was to create an efficient language (regarding both compilation speed and generated code) based on so-called structured programming, a concept which had recently become popular. Pascal has its roots in the ALGOL 60 language, but also introduced concepts and mechanisms which (on top of ALGOL's scalars and arrays) enabled programmers to define their own complex (structured) datatypes, and also made it easier to build dynamic and recursive data structures such as lists, trees and graphs. Important features included for this were records, enumerations, subranges, dynamically allocated variables with associated pointers, and sets. To make this possible and meaningful, Pascal has a strong typing on all objects, which means that one type of data cannot be converted or interpreted as another without explicit conversions. Similar mechanisms are standard in many programming languages today. Other languages that influenced Pascal's development were COBOL, Simula 67, and Wirth's own ALGOL W.
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 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 keyword itself, of course.)

[edit] Implementations

The first Pascal compiler was designed in Zürich for the CDC 6000 series mainframe computer family. Niklaus Wirth reports that a first attempt to implement it in Fortran in 1969 was unsuccessful due to Fortran's inadequacy to express complex data structures. The second attempt was formulated in the Pascal language itself and was operational by mid-1970. Many Pascal compilers since have been similarly self-hosting, that is, the compiler is itself written in Pascal, and the compiler is usually capable of recompiling itself when new features are added to the language, or when the compiler is to be ported to a new environment. The GNU Pascal compiler is one notable exception, being written in C.
The first successful port of the CDC Pascal compiler to another mainframe was completed by Welsh and Quinn at the QUB in 1972. The target was the ICL 1900 series. This compiler in turn was the parent of the Pascal compiler for the 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.
A completely new compiler was completed by Welsh et al. at QUB in 1977. It offered a source-language diagnostic feature (incorporating profiling, tracing and type-aware formatted postmortem dumps) that was implemented by Findlay and Watt at Glasgow University. This implementation was ported in 1980 to the ICL 2900 series by a team based at Southampton University and Glasgow University. The Standard Pascal Model Implementation was also based on this compiler, having been adapted, by Welsh and Hay at Manchester University in 1984, to check rigorously for conformity to the BSI 6192/ISO 7185 Standard and to generate code for a portable abstract machine.
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.
To propagate the language rapidly, a compiler "porting kit" was created in Zurich that included a compiler that generated code for a "virtual" stack machine (i.e. code that lends itself to reasonably efficient interpretation), along with an interpreter for that code - the Pascal-P system. The P-system compilers were termed Pascal-P1, Pascal-P2, Pascal-P3, and Pascal-P4. Pascal-P1 was the first version, and Pascal-P4 was the last to come from Zurich.
The Pascal-P4 compiler/interpreter can still be run and compiled on systems compatible with original Pascal. However, it only accepts a subset of the Pascal language.
Pascal-P5, created outside of the Zurich group, accepts the full Pascal language and includes ISO 7185 compatibility.
UCSD Pascal branched off Pascal-P2, where Kenneth Bowles utilized it to create the interpretive UCSD p-System
A compiler based on the Pascal-P4 compiler, which created native binaries, was released for the IBM System/370 mainframe computer by the Australian Atomic Energy Commission; it was called the "AAEC Pascal Compiler" after the abbreviation of the name of the Commission.
In the early 1980s, Watcom Pascal was developed, also for the IBM System 370.
IP Pascal was an implementation of the Pascal programming language using Micropolis DOS, but was moved rapidly to CP/M 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 which is also compatible with the original Pascal implementation (which is standardized as ISO 7185).
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.
Apple Computer created its own Lisa Pascal for the Lisa Workshop in 1982 and ported this compiler to the Apple Macintosh and MPW in 1985. In 1985 Larry Tesler, in consultation with Niklaus Wirth, defined Object Pascal and these extensions were incorporated in both the Lisa Pascal and Mac Pascal compilers.
In the 1980s Anders Hejlsberg wrote the Blue Label Pascal compiler for the Nascom-2. A reimplementation of this compiler for the IBM PC was marketed under the names Compas Pascal and PolyPascal before it was acquired by Borland. Renamed to Turbo Pascal it became hugely popular, thanks in part to an aggressive pricing strategy and in part to having one of the first full-screen Integrated development environments, and fast turnaround-time (just seconds to compile, link, and run.) Additionally, it was written and highly optimized entirely in assembly language, making it smaller and faster than much of the competition. 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.^[6][7] 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.
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.) The first versions of the Delphi language were accordingly named Object Pascal. The main additions compared to the older OOP extensions were a reference-based object model, virtual constructors and destructors, and properties. Several other compilers also implement this dialect.
Turbo Pascal, and other derivatives with units or module concepts are modular languages. However, it does not provide a nested module concept or qualified import and export of specific symbols.
Super Pascal was a variant which added non-numeric labels, a return statement and expressions as names of types.
Standards
In 1983, the language was standardized, in the international standard IEC/ISO 7185, and several local country specific standards, including the American ANSI/IEEE770X3.97-1983, and ISO 7185:1983. These two standards differed only in that the ISO standard included a "level 1" extension for conformant arrays, where ANSI did not allow for this extension to the original (Wirth version) language. In 1989, ISO 7185 was revised (ISO 7185:1990) to correct various errors and ambiguities found in the original document.
In 1990, an extended Pascal standard was created as ISO/IEC 10206. In 1993 the ANSI standard was replaced by the ANSI organization with a "pointer" to the ISO 7185:1990 standard, effectively ending its status as a different standard.
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.
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. This language was documented in "The Pascal Report", the second part of the "Pascal users manual and report".
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.
The IBM-PC versions of the language began to differ with the advent of UCSD Pascal, an interpreted implementation that featured several extensions to the language, along with several omissions and changes. Many UCSD language features survive today, including in Borland's dialect.

[edit] 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 out several features of the full language. For example, procedures and functions used as parameters, undiscriminated variant records, packing, dispose, interprocedural gotos and other features of the full compiler were omitted.
UCSD Pascal, under Professor Kenneth Bowles, was based on the Pascal-P2 kit, and consequently shared several of the Pascal-P language restrictions. UCSD Pascal was later adopted as Apple Pascal, and continued through several versions there. Although UCSD Pascal actually expanded the subset Pascal in the Pascal-P kit by adding back standard Pascal constructs, it was still not a complete standard installation of Pascal.
Borland's Turbo Pascal, written by Anders Hejlsberg, was written in assembly language independent of UCSD or the Zurich compilers. However, it adopted much of the same subset and extensions as the UCSD compiler. This is probably because the UCSD system was the most common Pascal system suitable for developing applications on the resource-limited microprocessor systems available at that time.

[edit] List of related standards

• ISO 8651-2:1988 Information processing systems—Computer graphics—Graphical Kernel System (GKS) language bindings—Part 2: Pascal

[edit] Reception

Pascal generated a wide variety of responses in the computing community, both critical and complimentary.

[edit] Criticism

While very popular (although more so in the 1980s and early 1990s than now), implementations of Pascal which closely followed Wirth's initial definition of the language were widely criticized for being unsuitable for use outside of teaching. Brian Kernighan, who popularized the C language, outlined his most notable criticisms of Pascal as early as 1981, in his paper Why Pascal Is Not My Favorite Programming Language.^[10] The most serious problem, described in this article, seems that array sizes and string lengths were part of the type so it was not possible to write a function that would accept variable length arrays or even strings as parameters (like a sorting library, for instance). The author also criticized the unpredictable order of evaluation of boolean expressions, poor library support, lack of static variables and a number of smaller issues. Also, he stated that the language did not provide any simple constructs to "escape" (knowingly and forcibly ignore) restrictions and limitations where this is really necessary. (However, there is a feature of "record variants" that does allow such an "escape," though it is decidedly cumbersome.) More general complaints from other sources^[11][12] noted that the scope of declarations were not clearly defined in the original language definition, which sometimes had serious consequences when using forward declarations to define pointer types, or when record declarations lead to mutual recursion, or when an identifier may or may not have been used in an enumeration list. Another difficulty was that, like ALGOL 60, the language did not allow procedures or functions passed as parameters to pre-define what their parameters are supposed to be.
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 Macintosh operating system API had to deal in Pascal data types).

[edit] Reactions

Pascal continued to evolve, and most of Kernighan's points do not apply to versions of the language which were enhanced to be suitable for commercial product development, such as Borland's Turbo Pascal. Unfortunately, just as Kernighan predicted in his article, most of the extensions to fix these issues were incompatible from compiler to compiler. Since the early 1990s, however, the varieties seem to have condensed into two categories, ISO and Borland-like, a better eventual outcome than Kernighan foresaw.^{[original research?]}
Although Kernighan decried Pascal's lack of type escapes ("there is no escape" from "Why Pascal is not my Favorite Programming language"), the uncontrolled use of pointers and type escapes have become highly criticized features in their own right, and the languages Java, C# and others feature a sharp turn-around to the Pascal point of view. What these languages call "managed pointers" were in fact foreseen by Wirth with the creation of Pascal.
Based on his experience with Pascal (and earlier with ALGOL) Niklaus Wirth developed several more programming languages: Modula, Modula-2 and Oberon. These languages address some criticisms of Pascal, are intended for different user populations, and so on, but none has had the widespread impact on computer science and computer users as has Pascal, nor has any yet met with similar commercial success