Programming language: Difference between revisions

[pending revision]

Content deleted Content added

Inline

Revision as of 23:04, 27 June 2006

A programming language is an artificial language intended to be usable for controlling the behavior of a machine (often a computer). Like human languages, programming languages have syntactic and semantic rules used to define meaning. Programming languages are used to facilitate communication about the task of organizing and manipulating information, and to express algorithms precisely. Some authors restrict the term "programming language" to those languages that can express all possible algorithms;^[1] sometimes the term "computer language" is used for more limited artificial languages.

Thousands of different programming languages^[2] have been created and new ones are created every year. Few languages ever become sufficiently popular that they are used by more than a few people, but professional programmers are likely to use dozens of different languages during their careers.

Definitions

Authors disagree on the precise definition of programming language. Traits often examined are:

Function: A programming language is a language used to write computer programs, which instruct a computer to perform some kind of computation^[3].
Target: Programming languages differ from natural languages in that natural languages are only used for interaction between people, while programming languages also allow humans to communicate instructions to machines.
Constructs: Programming languages may contain constructs for defining and manipulating data structures or for controlling the flow of execution.
Expressive power: The theory of computation classifies languages by the computations they can express. All Turing complete languages can implement the same algorithms. These are often called general purpose programming languages. ANSI/ISO SQL and Charity are examples of languages that are not Turing complete yet often called programming languages.^{[citation needed]}

Other computer languages, such as HTML, are sometimes informally referred to as programming languages.

Purpose

Programming languages differ from most other forms of human expression in that they require a greater degree of precision and completeness. When using a natural language authors can be ambiguous and make small errors and still expect their intent to be understood. However, computers do exactly what they are told to do, and cannot understand the code the programmer "intended" to write. The combination of the language definition, the program, and the program's inputs fully specify the external behavior that occurs when the program is 'executed'.^{[citation needed]}

Many languages have been designed from scratch, altered to meet new needs, combined with other languages, and eventually fallen into disuse. Although there have been attempts to design one "universal" computer language that serves all purposes (e.g., PL/I), all of them have failed to be accepted in this role.^{[citation needed]} The need for diverse computer languages arises from the diversity of contexts in which languages are used:

Programs range from tiny scripts written by individual hobbyists to huge systems written by hundreds of programmers.
Programmers range in expertise from novices, who need simplicity above all else, to experts, who may be comfortable with considerable complexity.
Programs may need to extract the right amount of performance on platforms ranging from tiny microcontrollers to supercomputers.
Programs may be written at one time, to reflect some exacting constraints, and then not changed for generations, until these constraints change, or they may undergo nearly constant modification.
Finally, programmers may simply differ in their tastes or habits: they may be accustomed to discussing problems and expressing them in a particular language.

One common trend in the development of programming languages has been to add more ability to solve problems using a higher level of abstraction. The earliest programming languages were tied very closely to the underlying hardware of the computer.^{[citation needed]} As new programming languages have developed, features have been added that let programmers express ideas that are more removed from simple translation into underlying hardware instructions.^{[citation needed]} Because programmers are less tied to the needs of the computer, their programs can do more computing with less effort from the programmer. This lets them write more programs in the same amount of time. ^[4]

Natural language processors have been proposed as a way to eliminate the need for a specialized language for programming.^{[citation needed]} However, this goal remains distant and its benefits are open to debate. Edsger Dijkstra took the position that the use of a formal language is essential to prevent the introduction of meaningless constructs, and dismissed natural language programming as "foolish."^[5] Alan Perlis was similarly dismissive of the idea.^[6]

Elements

Syntax

A programming language's surface form is its syntax. Most programming languages are purely textual; they use sequences of "words" and "punctuation marks", like written natural languages. Some programming languages are more graphical, using spatial relationships between symbols.^{[citation needed]}

The syntax of a language describes the possible combinations of symbols that form a syntactically correct program. The meaning given to a combination of symbols is handled by semantics. Since most languages are textual, this article discusses textual syntax.

Programming language syntax is usually defined using a combination of regular expressions (for lexical structure)^{[citation needed]} and Backus-Naur Form (for grammatical structure).^{[citation needed]} Below is a simple grammar, based on Lisp:

expression ::= atom | list atom ::= number | symbol number ::= ['0'-'9']+ symbol ::= ['A'-'Z''a'-'z'].* list ::= '(' expression* ')'

This grammar specifies:

an expression is an atom or a list;
an atom is a number or a symbol;
a number is one or more digits;
a symbol is a letter followed by zero or more of any characters; and
a list is a pair of parentheses, with any number of expressions inside it.

The following are examples of well-formed token sequences in this grammar: '12345', '()', '(a b c232 (1))'

Not all syntactically correct programs are semantically correct. Many syntactically correct programs are nonetheless ill-formed, per the language's rules; and may (depending on the language specification and the soundness of the implementation) result in an error on translation or execution. In some cases, such programs may exhibit undefined behavior.^{[citation needed]} Even when a program is well-defined within a language, it may still have a meaning that is not intended by the person who wrote it.

Using natural language as an example, it may not be possible to assign a meaning to a grammatically correct sentence or the sentence may be false:

"Colorless green ideas sleep furiously." is grammatically well-formed but has no generally accepted meaning.
"John is a married bachelor." is grammatically well-formed but expresses a meaning that cannot be true.

The following C language fragment is syntactically correct, but performs an operation that is not semantically defined (because p is a null pointer, the operations p->real and p->im have no meaning):

complex *p = NULL;
complex abs_p = sqrt (p->real * p->real + p->im * p->im);

Type system

A type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact.^{[citation needed]} This generally includes a description of the data structures that can be constructed in the language. The design and study of type systems using formal mathematics is known as type theory.

Internally, all data in modern digital computers are stored simply as zeros or ones (binary). The data typically represent information in the real world such as names, bank accounts and measurements, so the low-level binary data are organized by programming languages into these high-level concepts as data types.^{[citation needed]} There are also more abstract types whose purpose is just to warn the programmer about semantically meaningless statements or verify safety properties of programs.^{[citation needed]}

Languages can be classified with respect to their type systems.

Untyped and typed

A language is typed if operations defined for one data type cannot be performed on values of another data type.^{[citation needed]} For example, "word" is a string. In most programming languages, dividing a number by a string has no meaning. Most modern programming languages will therefore reject any program attempting to perform such an operation. In some languages, the meaningless operation will be detected statically, while in others, it will be detected dynamically.

By opposition, an untyped language, such as most assembly languages, allows any operation to be performed on any data type.^{[citation needed]}

In practice, while few languages are considered typed from the point of view of type theory,^{[citation needed]} most modern languages offer a degree of typing.

Static and dynamic

Static typing defines all expressions to have one type, at compile-time.^{[citation needed]} For example, 1 and (2+2) are integer expressions; they cannot be passed to a function that expects a string, or stored in a variable that is defined to hold dates.

Statically-typed languages can be manifestly typed or type-inferred. In the first case, the programmer must explicitly write types at certain textual positions (for example, at variable declarations).^{[citation needed]} In the second case, the compiler infers the types of expressions and declarations based on context.^{[citation needed]} Most mainstream statically-typed languages, such as C++ and Java, are manifestly typed.^{[citation needed]} Complete type inference has traditionally been associated with less mainstream languages, such as Haskell and ML.^{[citation needed]} However, many manifestly typed languages support type inference in certain cases; for example, Java and C# both infer instantiations of generic types for certain kinds of expressions.^{[citation needed]}

Dynamic typing, also called latent typing, assigns types when the program is run; in other words, types are associated with runtime values rather than textual expressions.^{[citation needed]} As with type-inferred languages, dynamically typed languages do not require the programmer to write explicit type annotations on expressions. Among other things, this may permit a single variable to refer to values of different types at different points in the program execution. However, type errors cannot be automatically detected until a piece of code is actually executed, making debugging more difficult.^{[citation needed]} Lisp, JavaScript, and Python are dynamically typed.^{[citation needed]}

Weak and strong

Weak typing allows a value of one type to be treated as another, for example treating a string as a number.^{[citation needed]} This can be useful, but it can also cause bugs; such languages are often termed unsafe.^{[citation needed]} C, Perl, and most assembly languages are weakly typed.^{[citation needed]}

Strong typing prevents the above. Attempting to mix types raises an error.^{[citation needed]} Strongly-typed languages are often termed type-safe or safe,^{[citation needed]} but they do not make bugs impossible. Ada, Python, and ML are strongly typed.^{[citation needed]}

Strong and static are generally considered orthogonal concepts, but usage in the literature differs. Some use the term strongly typed to mean strongly, statically typed, or, even more confusingly, to mean simply statically typed. Thus C has been called strongly typed, although most would call it weakly, statically typed.^[7]^[8]

Execution semantics

Once data has been specified, the machine must be instructed to perform operations on the data. The execution semantics of a language defines how and when the various constructs of a language should produce a program behavior.^{[citation needed]}

For example, the semantics may define the strategy by which expressions are evaluated to values, or the manner in which control structures conditionally execute statements.

Standard library

Most programming languages have an associated standard library, which is conventionally made available in all implementations of the language. Standard libraries typically include definitions for commonly used algorithms, data structures, and mechanisms for input and output.

Often, a language's standard library is treated as part of the language by its designers and users. Most language specifications define a standard library that must be made available in all conforming implementations.^{[citation needed]} The line between a language and its standard library is therefore porous. Indeed, some languages are designed so that the meanings of certain syntactic constructs cannot even be described without referring to the standard library. For example, in Java, a string literal is defined as an instance of the java.lang.String class from the standard library;^{[citation needed]} similarly, in Smalltalk, an anonymous function expression (a "block") constructs an instance of the standard library's BlockContext class.^{[citation needed]} Conversely, Scheme contains multiple coherent subsets that suffice to construct the rest of the language as library macros, and so the language designers do not even bother to say which portions of the language must be implemented as language constructs, and which must be implemented as parts of the standard library.^{[citation needed]}

Practice

A language's designers and users must construct a number of artifacts that govern and enable the practice of programming. The most important of these artifacts are the language's specification and implementation.

Specification

The specification of a programming language is intended to provide a definition that language users and implementors can use to interpret the behavior of programs when reading their source code.

A programming language specification can take several forms, including the following:

An explicit definition of the syntax and semantics of the language. While syntax is commonly specified using a formal grammar, semantic definitions may be written in natural language (e.g., the C language), or a formal semantics (e.g., the Standard ML ^[9]and Scheme^[10] specifications).
A description of the behavior of a translator for the language (e.g., C++^{[citation needed]} and Fortran^{[citation needed]}). The syntax and semantics of the language has to be inferred from this description, which may be written in natural or a formal language.
A model implementation, sometimes written in the language being specified (e.g., Prolog^{[citation needed]}). The syntax and semantics of the language are explicit in the behavior of the model implementation.

Implementation

An implementation of a programming language provides a way to execute that program on one or more configurations of hardware and software. There are, broadly, two approaches to programming language implementation: compilation and interpretation.^{[citation needed]} Some implementations support both interpretation and compilation.^{[citation needed]}

An interpreter parses a computer program and executes it directly.^{[citation needed]} This can be imagined as following the instructions of the program line-by-line. By contrast, a compiler translates the program into another language, which may in turn be either interpreted or compiled.^{[citation needed]} Some compilers translate a program into machine code (instructions that can be interpreted directly by a piece of computing hardware).^{[citation needed]}

Programs compiled to machine code usually run faster than interpreted ones, because the work of parsing and translating the programming language has already been done. However, interpreters are frequently easier to write than compilers, and it is often easier to construct interactive debuggers and other programming tools for interpreters than for compiled code.^{[citation needed]}

Many modern languages use a mixture of compilation and interpretation. The "compiler" for a bytecode-based language translates the source code into a partially compiled intermediate format, which is later run by a fast interpreter called a virtual machine.^{[citation needed]} Some "interpreters" actually use a just-in-time compiler, which compiles the code to machine language immediately before running it.^{[citation needed]} These techniques are often combined. An unusual case is Forth, which is described as incrementally compiled.^{[citation needed]} Like other aspects of programming languages, "compiled" and "interpreted" may be best understood as opposite ends of a spectrum, rather than as discrete options.

History

Early developments

In some sense, the first programming languages predate the modern computer. At a practical level, punch cards were used by the beginning of the 20th Century to encode data and perform limited mechanical processing;^{[citation needed]} even before that "programmable" looms and player piano scrolls implemented limited domain-specific programming languages.^{[citation needed]} In the 1930s and 1940s, the formalisms of Alonzo Church's lambda calculus and Alan Turing's Turing machines provided mathematical abstractions for expressing algorithms;^{[citation needed]} the lambda calculus remains influential in language design today.^{[citation needed]}

In the 1940s the first recognizably modern, electrically powered computers were created.^{[citation needed]} Their limited speed and memory capacity required programmers to write hand tuned assembly language programs.^{[citation needed]} During the 1950s, the first three modern programming languages were developed: FORTRAN, LISP and COBOL.^{[citation needed]} Variants of all of these are still in general use, and importantly, each has strongly influenced the development of later languages.^{[citation needed]} At the end of the 1950s, the language formalized as Algol 60 was introduced, and most modern programming languages are, in many respects, descendents of Algol.^{[citation needed]}

The period from the 1960s to the late 1970s brought the development of the major language paradigms now in use, though many aspects were refinements of ideas in the very first programming languages:

APL introduced array programming, and influenced functional programming.^[11]
In the 1960s, Simula was the first language designed to support object-oriented programming;^{[citation needed]} in the mid-1970s, Smalltalk followed with the first "purely" object-oriented language.^{[citation needed]}
C was developed between 1969 and 1973 as a systems programming language,^{[citation needed]} and remains popular.^[12]
Prolog, designed in 1972, was the first logic programming language.^{[citation needed]}
In 1978, ML built a polymorphic type system on top of Lisp, pioneering statically typed functional programming languages.^{[citation needed]}

Each of these languages spawned an entire family of descendants, and most modern languages count at least one of them in their ancestry.

The 1960s and 1970s also saw considerable debate over the merits of "structured programming", which essentially meant programming without the use of GOTO.^{[citation needed]} Nearly all programmers now agree that, even in languages that provide GOTO, it is bad style to use it except in rare circumstances.^{[citation needed]}

Consolidation and growth

The 1980s were years of relative consolidation. C++ combined object-oriented and systems programming.^{[citation needed]} The United States government standardized Ada, a systems programming language intended for use by defense contractors.^{[citation needed]} In Japan and elsewhere, vast sums were spent investigating so-called "fifth generation" languages that incorporated logic programming constructs.^{[citation needed]} The functional languages community moved to standardize ML and Lisp.^{[citation needed]} Rather than inventing new paradigms, all of these movements elaborated upon the ideas invented in the previous decade.

One important trend in language design during the 1980s was an increased focus on programming for large-scale systems through the use of modules, or large-scale organizational units of code.^{[citation needed]} Modula-3, Ada, and ML all developed notable module systems in the 1980s.^{[citation needed]} Module systems were often wedded to generic programming constructs.^{[citation needed]}

The rapid growth of the Internet in the mid-1990's created an opportunity for new languages to be adopted. In particular, the Java programming language rose to popularity because of its early integration with web browsers,^{[citation needed]} and various scripting languages achieved widespread use in developing customized applications for web servers.^{[citation needed]} Neither of these developments represented much fundamental novelty in language design, merely refinements in existing languages and paradigms.

Programming language evolution continues, in both industry and research. Current directions include mechanisms for adding security and reliability verification,^{[citation needed]} alternative mechanisms for modularity (mixins,^{[citation needed]} delegates,^{[citation needed]} aspects^{[citation needed]}), integration with databases,^{[citation needed]} and a focus on open source as a developmental philosophy.^{[citation needed]}

Taxonomies

There is no overarching classification scheme for programming languages. Any given programming language does not usually have a single ancestor language. Languages commonly arise by combining the elements of several predecessor languages with new ideas in circulation at the time.^{[citation needed]} Ideas that originate in one language will diffuse throughout a family of related languages, and then leap suddenly across familial gaps to appear in an entirely different family.

The task is further complicated by the fact that languages can be classified along multiple axes. For example, Java is both an object-oriented language (because it encourages object-oriented organization)^{[citation needed]} and a concurrent language (because it contains built-in constructs for running multiple threads in parallel).^{[citation needed]} Python is an object-oriented scripting language.^{[citation needed]}

In broad strokes, programming languages divide into programming paradigms and a classification by intended domain of use. Paradigms include procedural programming, object-oriented programming, functional programming, and logic programming;^{[citation needed]} some languages are hybrids of paradigms or multi-paradigmatic.^{[citation needed]} An assembly language is not so much a paradigm as a direct model of an underlying machine architecture.^{[citation needed]} By purpose, programming languages might be considered general purpose, system programming languages, scripting languages, domain-specific languages, or concurrent/distributed languages (or a combination of these). Some general purpose languages were designed largely with educational goals.^{[citation needed]}

Footnotes

^ In mathematical terms, this means the programming language is Turing-complete MacLennan, Bruce J. (1987). Principles of Programming Languages. Oxford University Press. p. 1. ISBN 0195113063.
^ As of May 2006 The Encyclopedia of Computer Languages by Murdoch University, Australia lists 8512 computer languages.
^ ACM SIGPLAN (2003). "Bylaws of the Special Interest Group on Programming Languages of the Association for Computing Machinery". Retrieved 2006-06-19., The scope of SIGPLAN is the theory, design, implementation, description, and application of computer programming languages - languages that permit the specification of a variety of different computations, thereby providing the user with significant control (immediate or delayed) over the computer's operation.
^ Frederick P. Brooks, Jr.: The Mythical Man-Month, Addison-Wesley, 1982, pp. 93-94
^ Dijkstra, Edsger W. On the foolishness of "natural language programming." EWD667.
^ Perlis, Alan, Epigrams on Programming. SIGPLAN Notices Vol. 17, No. 9, September 1982, pp. 7-13
^ "Revised Report on the Algorithmic Language Scheme (February 20, 1998)". Retrieved June 9. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
^ Luca Cardelli and Peter Wegner. "On Understanding Types, Data Abstraction, and Polymorphism". Manuscript (1985). Retrieved June 9. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
^ Milner, R. (1997). The Definition of Standard ML (Revised). MIT Press. ISBN 0262631814. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Kelsey, Richard (1998). "Section 7.2 Formal semantics". Revised⁵ Report on the Algorithmic Language Scheme. Retrieved 2006-06-09. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
^ Richard L. Wexelblat: History of Programming Languages, Academic Press, 1981, chapter XIV.
^ François Labelle. "Programming Language Usage Graph". Sourceforge. Retrieved June 21. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help). This comparison analyzes trends in number of projects hosted by a popular community programming repository. During most years of the comparison, C leads by a considerable margin; in 2006, Java overtakes C, but the combination of C/C++ still leads considerably.

References

David Gelernter, Suresh Jagannathan: Programming Linguistics, The MIT Press 1990.
Samuel N. Kamin: Programming Languages: An Interpreter-Based Approach, Addison-Wesley 1990.
Shriram Krishnamurthi: Programming Languages: Application and Interpretation, online publication.
Burce J. MacLennan: Principles of Programming Languages, Harcourt Brace Jovanovich 1987.
John C. Mitchell: Concepts in Programming Languages, Cambridge University Press 2002.
Benjamin C. Pierce: Types and Programming Languages, The MIT Press 2002.
Ravi Sethi: Programming Languages: Concepts and Constructs, 2nd ed., Addison-Wesley 1996.
Richard L. Wexelblat (ed.): History of Programming Languages, Academic Press 1981.

External links

99 Bottles of Beer - a collection of implementations in many languages
Computer Languages History graphical chart
Dictionary of Programming Languages
History of Programming Languages (HOPL)
Open Directory - Computer Programming Languages
Programming Language Comparison
Syntax Patterns for Various Languages

Template:Link FA Template:Link FA Template:Link FA

[1] In mathematical terms, this means the programming language is Turing-complete MacLennan, Bruce J. (1987). Principles of Programming Languages. Oxford University Press. p. 1. ISBN 0195113063.

[2] As of May 2006 The Encyclopedia of Computer Languages by Murdoch University, Australia lists 8512 computer languages.

[3] ACM SIGPLAN (2003). "Bylaws of the Special Interest Group on Programming Languages of the Association for Computing Machinery". Retrieved 2006-06-19., The scope of SIGPLAN is the theory, design, implementation, description, and application of computer programming languages - languages that permit the specification of a variety of different computations, thereby providing the user with significant control (immediate or delayed) over the computer's operation.

[4] Frederick P. Brooks, Jr.: The Mythical Man-Month, Addison-Wesley, 1982, pp. 93-94

[5] Dijkstra, Edsger W. On the foolishness of "natural language programming." EWD667.

[6] Perlis, Alan, Epigrams on Programming. SIGPLAN Notices Vol. 17, No. 9, September 1982, pp. 7-13

[7] "Revised Report on the Algorithmic Language Scheme (February 20, 1998)". Retrieved June 9. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

[8] Luca Cardelli and Peter Wegner. "On Understanding Types, Data Abstraction, and Polymorphism". Manuscript (1985). Retrieved June 9. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)

[9] Milner, R. (1997). The Definition of Standard ML (Revised). MIT Press. ISBN 0262631814. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

[10] Kelsey, Richard (1998). "Section 7.2 Formal semantics". Revised⁵ Report on the Algorithmic Language Scheme. Retrieved 2006-06-09. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

[11] Richard L. Wexelblat: History of Programming Languages, Academic Press, 1981, chapter XIV.

[12] François Labelle. "Programming Language Usage Graph". Sourceforge. Retrieved June 21. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help). This comparison analyzes trends in number of projects hosted by a popular community programming repository. During most years of the comparison, C leads by a considerable margin; in 2006, Java overtakes C, but the combination of C/C++ still leads considerably.

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

@@ Line 10: / Line 10: @@
 *''Target:''  Programming languages differ from [[natural language]]s in that natural languages are only used for interaction between people, while programming languages also allow humans to communicate instructions to machines.
 *''Constructs:'' Programming languages may contain constructs for defining and manipulating [[data structure]]s or for controlling the [[control flow|flow of execution]].
-*''Expressive power:''  The [[theory of computation]] classifies languages by the computations they can express. All [[Turing complete]] languages can implement the same [[algorithm]]s.  These are often called [[general-purpose (programming language)|general purpose programming languages]]. [[American National Standards Institute|ANSI]]/[[International Organization for Standardization|ISO]] [[SQL]] and [[Charity programming language|Charity]] are examples of languages that are not Turing complete yet often called programming languages.
+*''Expressive power:''  The [[theory of computation]] classifies languages by the computations they can express. All [[Turing complete]] languages can implement the same [[algorithm]]s.  These are often called [[general-purpose (programming language)|general purpose programming languages]]. [[American National Standards Institute|ANSI]]/[[International Organization for Standardization|ISO]] [[SQL]] and [[Charity programming language|Charity]] are examples of languages that are not Turing complete yet often called programming languages.{{fact}}
 Other [[computer languages]], such as [[HTML]], are sometimes informally referred to as programming languages.
 ==Purpose==
-Programming languages differ from most other forms of human expression in that they require a greater degree of precision and completeness.  When using a natural language authors can be ambiguous and make small errors and still expect their intent to be understood. However, computers do exactly what they are told to do, and cannot understand the code the programmer "intended" to write. The combination of the language definition, the [[program]], and the program's inputs fully specify the external behavior that occurs when the program is 'executed'.
+Programming languages differ from most other forms of human expression in that they require a greater degree of precision and completeness.  When using a natural language authors can be ambiguous and make small errors and still expect their intent to be understood. However, computers do exactly what they are told to do, and cannot understand the code the programmer "intended" to write. The combination of the language definition, the [[program]], and the program's inputs fully specify the external behavior that occurs when the program is 'executed'.{{fact}}
-Many languages have been designed from scratch, altered to meet new needs, combined with other languages, and eventually fallen into disuse.  Although there have been attempts to design one "universal" computer language that serves all purposes (''e.g.'', [[PL/I]]), all of them have failed to be accepted in this role.  The need for diverse computer languages arises from the diversity of contexts in which languages are used:
+Many languages have been designed from scratch, altered to meet new needs, combined with other languages, and eventually fallen into disuse.  Although there have been attempts to design one "universal" computer language that serves all purposes (''e.g.'', [[PL/I]]), all of them have failed to be accepted in this role.{{fact}}  The need for diverse computer languages arises from the diversity of contexts in which languages are used:
 * Programs range from tiny scripts written by individual hobbyists to huge systems written by hundreds of programmers.
 * Programmers range in expertise from novices, who need simplicity above all else, to experts, who may be comfortable with considerable complexity.
@@ Line 24: / Line 24: @@
 * Finally, programmers may simply differ in their tastes or habits:  they may be accustomed to discussing problems and expressing them in a particular language.
-One common trend in the development of programming languages has been to add more ability to solve problems using a higher level of abstraction.  The earliest programming languages were tied very closely to the underlying hardware of the computer.  As new programming languages have developed, features have been added that let programmers express ideas that are more removed from simple translation into underlying hardware instructions.  Because programmers are less tied to the needs of the computer, their programs can do more computing with less effort from the programmer.  This lets them write more programs in the same amount of time. <ref> Frederick P. Brooks, Jr.:  ''The Mythical Man-Month,'' Addison-Wesley, 1982, pp. 93-94 </ref>
+One common trend in the development of programming languages has been to add more ability to solve problems using a higher level of abstraction.  The earliest programming languages were tied very closely to the underlying hardware of the computer.{{fact}}  As new programming languages have developed, features have been added that let programmers express ideas that are more removed from simple translation into underlying hardware instructions.{{fact}}  Because programmers are less tied to the needs of the computer, their programs can do more computing with less effort from the programmer.  This lets them write more programs in the same amount of time. <ref> Frederick P. Brooks, Jr.:  ''The Mythical Man-Month,'' Addison-Wesley, 1982, pp. 93-94 </ref>
-[[Natural language and computation|Natural language processor]]s have been proposed as a way to eliminate the need for a specialized language for programming. However, this goal remains distant and its benefits are open to debate. [[Edsger Dijkstra]] took the position that the use of a formal language is essential to prevent the introduction of meaningless constructs, and dismissed natural language programming as "foolish."<ref>Dijkstra, Edsger W. [http://www.cs.utexas.edu/users/EWD/transcriptions/EWD06xx/EWD667.html On the foolishness of "natural language programming."] EWD667.</ref> [[Alan Perlis]] was similarly dismissive of the idea.<ref>Perlis, Alan, [http://www-pu.informatik.uni-tuebingen.de/users/klaeren/epigrams.html Epigrams on Programming]. SIGPLAN Notices Vol. 17, No. 9, September 1982, pp. 7-13</ref>
+[[Natural language and computation|Natural language processor]]s have been proposed as a way to eliminate the need for a specialized language for programming.{{fact}}  However, this goal remains distant and its benefits are open to debate. [[Edsger Dijkstra]] took the position that the use of a formal language is essential to prevent the introduction of meaningless constructs, and dismissed natural language programming as "foolish."<ref>Dijkstra, Edsger W. [http://www.cs.utexas.edu/users/EWD/transcriptions/EWD06xx/EWD667.html On the foolishness of "natural language programming."] EWD667.</ref> [[Alan Perlis]] was similarly dismissive of the idea.<ref>Perlis, Alan, [http://www-pu.informatik.uni-tuebingen.de/users/klaeren/epigrams.html Epigrams on Programming]. SIGPLAN Notices Vol. 17, No. 9, September 1982, pp. 7-13</ref>
 ==Elements==
@@ Line 34: / Line 34: @@
 [[Image:Python_add5_syntax.png|thumb|right|292px|[[Syntax highlighting]] is often used to aid programmer recognition of elements of source code]]
 [[Image:Python_add5_parse.png|thumb|right|396px|[[Parse tree]] of Python code with inset tokenization]]
-A programming language's surface form is its '''[[syntax]]'''.  Most programming languages are purely textual; they use sequences of "words" and "punctuation marks", like written natural languages.  Some programming languages are more [[visual programming language|graphical]], using spatial relationships between symbols.
+A programming language's surface form is its '''[[syntax]]'''.  Most programming languages are purely textual; they use sequences of "words" and "punctuation marks", like written natural languages.  Some programming languages are more [[visual programming language|graphical]], using spatial relationships between symbols.{{fact}}
 The syntax of a language describes the possible combinations of symbols that form a syntactically correct program.  The meaning given to a combination of symbols is handled by semantics.  Since most languages are textual, this article discusses textual syntax.
-Programming language syntax is usually defined using a combination of [[regular expression]]s (for [[lexical analysis|lexical]] structure) and [[Backus-Naur Form]] (for [[context-free grammar|grammatical]] structure).  Below is a simple grammar, based on [[Lisp programming language|Lisp]]:
+Programming language syntax is usually defined using a combination of [[regular expression]]s (for [[lexical analysis|lexical]] structure){{fact}} and [[Backus-Naur Form]] (for [[context-free grammar|grammatical]] structure).{{fact}}  Below is a simple grammar, based on [[Lisp programming language|Lisp]]:
 <code>
@@ Line 57: / Line 57: @@
 The following are examples of well-formed token sequences in this grammar: '<code>12345</code>', '<code>()</code>', '<code>(a b c232 (1))</code>'
-Not all syntactically correct programs are semantically correct.  Many syntactically correct programs are nonetheless ill-formed, per the language's rules; and may (depending on the language specification and the soundness of the implementation) result in an error on translation or execution.  In some cases, such programs may exhibit [[undefined behavior]].  Even when a program is well-defined within a language, it may still have a meaning that is not intended by the person who wrote it.
+Not all syntactically correct programs are semantically correct.  Many syntactically correct programs are nonetheless ill-formed, per the language's rules; and may (depending on the language specification and the soundness of the implementation) result in an error on translation or execution.  In some cases, such programs may exhibit [[undefined behavior]].{{fact}}  Even when a program is well-defined within a language, it may still have a meaning that is not intended by the person who wrote it.
 Using [[natural language]] as an example, it may not be possible to assign a meaning to a grammatically correct sentence or the sentence may be false:
@@ Line 71: / Line 71: @@
 {{main|Type system}}
-A '''type system''' defines how a programming language classifies values and expressions into ''types'', how it can manipulate those types and how they interact.  This generally includes a description of the '''[[data structure]]s''' that can be constructed in the language.  The design and study of type systems using formal mathematics is known as ''[[type theory]]''.
+A '''type system''' defines how a programming language classifies values and expressions into ''types'', how it can manipulate those types and how they interact.{{fact}}  This generally includes a description of the '''[[data structure]]s''' that can be constructed in the language.  The design and study of type systems using formal mathematics is known as ''[[type theory]]''.
-Internally, all [[data]] in modern digital computers are stored simply as zeros or ones ([[Binary numeral system|binary]]). The data typically represent information in the real world such as names, bank accounts and measurements, so the low-level binary data are organized by programming languages into these high-level concepts as [[data type]]s. There are also more abstract types whose purpose is just to warn the programmer about semantically meaningless statements or verify safety properties of programs.
+Internally, all [[data]] in modern digital computers are stored simply as zeros or ones ([[Binary numeral system|binary]]). The data typically represent information in the real world such as names, bank accounts and measurements, so the low-level binary data are organized by programming languages into these high-level concepts as [[data type]]s.{{fact}}  There are also more abstract types whose purpose is just to warn the programmer about semantically meaningless statements or verify safety properties of programs.{{fact}}
 Languages can be classified with respect to their type systems.
@@ Line 79: / Line 79: @@
 ===== Untyped and typed =====
-A language is '''typed''' if operations defined for one data type cannot be performed on values of another data type. For example, "word" is a string. In most programming languages,
+A language is '''typed''' if operations defined for one data type cannot be performed on values of another data type.{{fact}}  For example, "word" is a string. In most programming languages, dividing a number by a string has no meaning. Most modern programming languages will therefore reject any program attempting to perform such an operation. In some languages, the meaningless operation will be detected statically, while in others, it will be detected dynamically.
-dividing a number by a string has no meaning. Most modern programming languages will therefore reject any program attempting to perform such an operation. In some languages, the meaningless operation will be detected statically, while in others, it will be detected dynamically.
-By opposition, an '''untyped''' language, such as most [[Assembly language|assembly languages]], allows any operation to be performed on any data type.
+By opposition, an '''untyped''' language, such as most [[Assembly language|assembly languages]], allows any operation to be performed on any data type.{{fact}}
-In practice, while few languages are considered typed from the point of view of [[type theory]], most modern languages offer a degree of typing.
+In practice, while few languages are considered typed from the point of view of [[type theory]],{{fact}} most modern languages offer a degree of typing.
 ===== Static and dynamic =====
-'''Static typing''' defines all expressions to have one type, at compile-time.  For example, 1 and (2+2) are integer expressions; they cannot be passed to a function that expects a string, or stored in a variable that is defined to hold dates.
+'''Static typing''' defines all expressions to have one type, at compile-time.{{fact}}  For example, 1 and (2+2) are integer expressions; they cannot be passed to a function that expects a string, or stored in a variable that is defined to hold dates.
-Statically-typed languages can be ''manifestly typed'' or ''[[type inference|type-inferred]]''.  In the first case, the programmer must explicitly write types at certain textual positions (for example, at variable [[declaration (computer science)|declaration]]s).  In the second case, the compiler ''infers'' the types of expressions and declarations based on context.  Most mainstream statically-typed languages, such as [[C Plus Plus|C++]] and [[Java programming language|Java]], are manifestly typed.  Complete type inference has traditionally been associated with less mainstream languages, such as [[Haskell]] and [[ML programming language|ML]].  However, many manifestly typed languages support type inference in certain cases; for example, [[Java programming language|Java]] and [[C Sharp|C#]] both infer instantiations of generic types for certain kinds of expressions.
+Statically-typed languages can be ''manifestly typed'' or ''[[type inference|type-inferred]]''.  In the first case, the programmer must explicitly write types at certain textual positions (for example, at variable [[declaration (computer science)|declaration]]s).{{fact}}  In the second case, the compiler ''infers'' the types of expressions and declarations based on context.{{fact}}  Most mainstream statically-typed languages, such as [[C Plus Plus|C++]] and [[Java programming language|Java]], are manifestly typed.{{fact}}  Complete type inference has traditionally been associated with less mainstream languages, such as [[Haskell]] and [[ML programming language|ML]].{{fact}}  However, many manifestly typed languages support type inference in certain cases; for example, [[Java programming language|Java]] and [[C Sharp|C#]] both infer instantiations of generic types for certain kinds of expressions.{{fact}}
-'''Dynamic typing''', also called ''latent typing'', assigns types when the program is run; in other words, types are associated with ''runtime values'' rather than ''textual expressions''.  As with type-inferred languages, dynamically typed languages do not require the programmer to write explicit type annotations on expressions.  Among other things, this may permit a single variable to refer to values of different types at different points in the program execution.  However, type errors cannot be automatically detected until a piece of code is actually executed, making debugging more difficult.  [[Lisp programming language|Lisp]], [[JavaScript]], and [[Python programming language|Python]] are dynamically typed.
+'''Dynamic typing''', also called ''latent typing'', assigns types when the program is run; in other words, types are associated with ''runtime values'' rather than ''textual expressions''.{{fact}}  As with type-inferred languages, dynamically typed languages do not require the programmer to write explicit type annotations on expressions.  Among other things, this may permit a single variable to refer to values of different types at different points in the program execution.  However, type errors cannot be automatically detected until a piece of code is actually executed, making debugging more difficult.{{fact}}  [[Lisp programming language|Lisp]], [[JavaScript]], and [[Python programming language|Python]] are dynamically typed.{{fact}}
 ===== Weak and strong =====
-''Weak typing'' allows a value of one type to be treated as another, for example treating a string as a number.  This can be useful, but it can also cause bugs; such languages are often termed ''unsafe''.  [[C programming language|C]], [[Perl]], and most [[assembly language|assembly languages]] are weakly typed.
+''Weak typing'' allows a value of one type to be treated as another, for example treating a string as a number.{{fact}}  This can be useful, but it can also cause bugs; such languages are often termed ''unsafe''.{{fact}}  [[C programming language|C]], [[Perl]], and most [[assembly language|assembly languages]] are weakly typed.{{fact}}
-''Strong typing'' prevents the above.  Attempting to mix types raises an error.  Strongly-typed languages are often termed ''type-safe'' or ''[[type safety|safe]]'', but they do not make bugs impossible.  [[Ada]], [[Python programming language|Python]], and [[ML programming language|ML]] are strongly typed.
+''Strong typing'' prevents the above.  Attempting to mix types raises an error.{{fact}}  Strongly-typed languages are often termed ''type-safe'' or ''[[type safety|safe]]'',{{fact}} but they do not make bugs impossible.  [[Ada]], [[Python programming language|Python]], and [[ML programming language|ML]] are strongly typed.{{fact}}
 ''Strong'' and ''static'' are generally considered orthogonal concepts, but usage in the literature differs.  Some use the term ''strongly typed'' to mean ''strongly, statically typed'', or, even more confusingly, to mean simply ''statically typed''.  Thus [[C programming language|C]] has been called strongly typed, although most would call it weakly, statically typed.<ref>{{cite web | url=http://www.schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-4.html | title=Revised Report on the Algorithmic Language Scheme (February 20, 1998) | accessdate=June 9 | accessyear=2006}}</ref><ref>{{cite web | url=http://citeseer.ist.psu.edu/cardelli85understanding.html | title=On Understanding Types, Data Abstraction, and Polymorphism | author=[[Luca Cardelli]] and [[Peter Wegner]] | work=Manuscript (1985) | accessdate=June 9 | accessyear=2006}}</ref>
@@ Line 104: / Line 103: @@
 ===Execution semantics===
-Once data has been specified, the machine must be instructed to perform operations on the data.  The ''execution semantics'' of a language defines how and when the various constructs of a language should produce a program behavior.
+Once data has been specified, the machine must be instructed to perform operations on the data.  The ''execution semantics'' of a language defines how and when the various constructs of a language should produce a program behavior.{{fact}}
 For example, the semantics may define the [[evaluation strategy|strategy]] by which expressions are evaluated to values, or the manner in which [[control structure]]s conditionally execute statements.
@@ Line 113: / Line 112: @@
 Most programming languages have an associated '''standard [[library (computer science)|library]]''', which is conventionally made available in all implementations of the language. Standard libraries typically include definitions for commonly used algorithms, data structures, and mechanisms for input and output.
-Often, a language's standard library is treated as part of the language by its designers and users.  Most language specifications define a standard library that must be made available in all conforming implementations.  The line between a language and its standard library is therefore porous.  Indeed, some languages are designed so that the meanings of certain syntactic constructs cannot even be described without referring to the standard library.  For example, in Java, a string literal is defined as an instance of the <tt>java.lang.String</tt> class from the standard library; similarly, in Smalltalk, an anonymous function expression (a "block") constructs an instance of the standard library's <tt>BlockContext</tt> class.  Conversely, [[Scheme programming language|Scheme]] contains multiple coherent subsets that suffice to construct the rest of the language as library macros, and so the language designers do not even bother to say which portions of the language must be implemented as language constructs, and which must be implemented as parts of the standard library.
+Often, a language's standard library is treated as part of the language by its designers and users.  Most language specifications define a standard library that must be made available in all conforming implementations.{{fact}}  The line between a language and its standard library is therefore porous.  Indeed, some languages are designed so that the meanings of certain syntactic constructs cannot even be described without referring to the standard library.  For example, in Java, a string literal is defined as an instance of the <tt>java.lang.String</tt> class from the standard library;{{fact}} similarly, in Smalltalk, an anonymous function expression (a "block") constructs an instance of the standard library's <tt>BlockContext</tt> class.{{fact}}  Conversely, [[Scheme programming language|Scheme]] contains multiple coherent subsets that suffice to construct the rest of the language as library macros, and so the language designers do not even bother to say which portions of the language must be implemented as language constructs, and which must be implemented as parts of the standard library.{{fact}}
 == Practice ==
@@ Line 133: / Line 132: @@
    | year = 1997
    | id = ISBN 0262631814 }}</ref>and [[Scheme programming language|Scheme]]<ref>{{cite web|first=Richard |last=Kelsey|coauthors=William Clinger and Jonathan Rees|title=Section 7.2  Formal semantics|work=Revised<sup>5</sup> Report on the Algorithmic Language Scheme|url = http://www.schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-10.html#%_sec_7.2| year=1998|month=February|accessdate=2006-06-09}}</ref> specifications).
-* A description of the behavior of a [[compiler|translator]] for the language (e.g., the [[C++]] and [[Fortran]]).  The syntax and semantics of the language has to be inferred from this description, which may be written in natural or a formal language.
+* A description of the behavior of a [[compiler|translator]] for the language (e.g., [[C++]]{{fact}} and [[Fortran]]{{fact}}).  The syntax and semantics of the language has to be inferred from this description, which may be written in natural or a formal language.
-* A ''model'' implementation, sometimes written in the language being specified (e.g., the [[Prolog]]). The syntax and semantics of the language are explicit in the behavior of the model implementation.
+* A ''model'' implementation, sometimes written in the language being specified (e.g., [[Prolog]]{{fact}}). The syntax and semantics of the language are explicit in the behavior of the model implementation.
 ===Implementation===
 {{main|Programming language implementation}}
-An '''implementation''' of a programming language provides a way to execute that program on one or more configurations of hardware and software.  There are, broadly, two approaches to programming language implementation: ''[[compiler|compilation]]'' and ''[[interpreter (computing)|interpretation]]''.  Some implementations support both interpretation and compilation.
+An '''implementation''' of a programming language provides a way to execute that program on one or more configurations of hardware and software.  There are, broadly, two approaches to programming language implementation: ''[[compiler|compilation]]'' and ''[[interpreter (computing)|interpretation]]''.{{fact}}  Some implementations support both interpretation and compilation.{{fact}}
-An interpreter [[parsing|parses]] a computer program and executes it directly.  This can be imagined as following the instructions of the program line-by-line.  By contrast, a compiler translates the program into another language, which may in turn be either interpreted or compiled.  Some compilers translate a program into [[machine code]] (instructions that can be interpreted directly by a piece of computing [[hardware]]).
+An interpreter [[parsing|parses]] a computer program and executes it directly.{{fact}}  This can be imagined as following the instructions of the program line-by-line.  By contrast, a compiler translates the program into another language, which may in turn be either interpreted or compiled.{{fact}}  Some compilers translate a program into [[machine code]] (instructions that can be interpreted directly by a piece of computing [[hardware]]).{{fact}}
-Programs compiled to machine code usually run faster than interpreted ones, because the work of parsing and translating the programming language has already been done.  However, interpreters are frequently easier to write than compilers, and it is often easier to construct interactive [[debugger]]s and other programming tools for interpreters than for compiled code.
+Programs compiled to machine code usually run faster than interpreted ones, because the work of parsing and translating the programming language has already been done.  However, interpreters are frequently easier to write than compilers, and it is often easier to construct interactive [[debugger]]s and other programming tools for interpreters than for compiled code.{{fact}}
-Many modern languages use a mixture of compilation and interpretation.  The "compiler" for a [[bytecode]]-based language translates the source code into a partially compiled intermediate format, which is later run by a fast interpreter called a [[virtual machine]].   Some "interpreters" actually use a [[just-in-time compiler]], which compiles the code to machine language immediately before running it.  These techniques are often combined.  An unusual case is [[Forth programming language|Forth]], which is described as incrementally compiled.  Like other aspects of programming languages, "compiled" and "interpreted" may be best understood as opposite ends of a spectrum, rather than as discrete options.
+Many modern languages use a mixture of compilation and interpretation.  The "compiler" for a [[bytecode]]-based language translates the source code into a partially compiled intermediate format, which is later run by a fast interpreter called a [[virtual machine]].{{fact}}   Some "interpreters" actually use a [[just-in-time compiler]], which compiles the code to machine language immediately before running it.{{fact}}  These techniques are often combined.  An unusual case is [[Forth programming language|Forth]], which is described as incrementally compiled.{{fact}}  Like other aspects of programming languages, "compiled" and "interpreted" may be best understood as opposite ends of a spectrum, rather than as discrete options.
 == History ==
@@ Line 150: / Line 149: @@
 === Early developments ===
-In some sense, the first programming languages predate the modern computer. At a practical level, punch cards were used by the beginning of the 20th Century to encode data and perform limited mechanical processing; even before that "programmable" looms and [[player piano]] scrolls implemented limited [[domain-specific programming language]]s.  In the 1930s and 1940s, the formalisms of [[Alonzo Church]]'s [[lambda calculus]] and [[Alan Turing]]'s [[Turing machine]]s provided mathematical abstractions for expressing [[algorithm]]s; the lambda calculus remains influential in language design today.
+In some sense, the first programming languages predate the modern computer. At a practical level, punch cards were used by the beginning of the 20th Century to encode data and perform limited mechanical processing;{{fact}} even before that "programmable" looms and [[player piano]] scrolls implemented limited [[domain-specific programming language]]s.{{fact}}  In the 1930s and 1940s, the formalisms of [[Alonzo Church]]'s [[lambda calculus]] and [[Alan Turing]]'s [[Turing machine]]s provided mathematical abstractions for expressing [[algorithm]]s;{{fact}} the lambda calculus remains influential in language design today.{{fact}}
-In the 1940s the first recognizably modern, electrically powered computers were created.  Their limited speed and memory capacity required programmers to write hand tuned [[assembly language]] programs.   During the [[1950s]], the first three modern programming languages were developed: [[FORTRAN programming language|FORTRAN]], [[LISP programming language|LISP]] and [[COBOL programming language|COBOL]].  Variants of all of these are still in general use, and importantly, each has strongly influenced the development of later languages.  At the end of the 1950s, the language formalized as [[Algol 60]] was introduced, and most modern programming languages are, in many respects, descendents of Algol.
+In the 1940s the first recognizably modern, electrically powered computers were created.{{fact}}  Their limited speed and memory capacity required programmers to write hand tuned [[assembly language]] programs.{{fact}}   During the [[1950s]], the first three modern programming languages were developed: [[FORTRAN programming language|FORTRAN]], [[LISP programming language|LISP]] and [[COBOL programming language|COBOL]].{{fact}}  Variants of all of these are still in general use, and importantly, each has strongly influenced the development of later languages.{{fact}}  At the end of the 1950s, the language formalized as [[Algol 60]] was introduced, and most modern programming languages are, in many respects, descendents of Algol.{{fact}}
 === Refinement ===
 The period from the 1960s to the late 1970s brought the development of the major language paradigms now in use, though many aspects were refinements of ideas in the very first programming languages:
 *[[APL]] introduced ''[[array programming]]'', and influenced [[functional programming]].<ref>Richard L. Wexelblat: ''History of Programming Languages'', Academic Press, 1981, chapter XIV.</ref>
-*In the 1960s, [[Simula programming language|Simula]] was the first language designed to support ''[[object-oriented programming]]''; in the mid-1970s, [[Smalltalk programming language|Smalltalk]] followed with the first "purely" object-oriented language.
+*In the 1960s, [[Simula programming language|Simula]] was the first language designed to support ''[[object-oriented programming]]'';{{fact}} in the mid-1970s, [[Smalltalk programming language|Smalltalk]] followed with the first "purely" object-oriented language.{{fact}}
-*[[C programming language|C]] was developed between [[1969]] and [[1973]] as a ''[[systems programming]]'' language, and remains popular.<ref>{{cite web | url=http://www.cs.berkeley.edu/~flab/languages.html | author=François Labelle | title=Programming Language Usage Graph | work=[[Sourceforge]] | accessdate=June 21 | accessyear=2006}}.  This comparison analyzes trends in number of projects hosted by a popular community programming repository.  During most years of the comparison, C leads by a considerable margin; in 2006, Java overtakes C, but the combination of C/C++ still leads considerably.</ref>
+*[[C programming language|C]] was developed between [[1969]] and [[1973]] as a ''[[systems programming]]'' language,{{fact}} and remains popular.<ref>{{cite web | url=http://www.cs.berkeley.edu/~flab/languages.html | author=François Labelle | title=Programming Language Usage Graph | work=[[Sourceforge]] | accessdate=June 21 | accessyear=2006}}.  This comparison analyzes trends in number of projects hosted by a popular community programming repository.  During most years of the comparison, C leads by a considerable margin; in 2006, Java overtakes C, but the combination of C/C++ still leads considerably.</ref>
-*[[Prolog programming language|Prolog]], designed in [[1972]], was the first ''[[logic programming]]'' language.
+*[[Prolog programming language|Prolog]], designed in [[1972]], was the first ''[[logic programming]]'' language.{{fact}}
-*In 1978, [[ML programming language|ML]] built a polymorphic type system on top of Lisp, pioneering ''[[static typing|statically typed]] [[functional programming]]'' languages.
+*In 1978, [[ML programming language|ML]] built a polymorphic type system on top of Lisp, pioneering ''[[static typing|statically typed]] [[functional programming]]'' languages.{{fact}}
 Each of these languages spawned an entire family of descendants, and most modern languages count at least one of them in their ancestry.
-The 1960s and 1970s also saw considerable debate over the merits of "[[structured programming]]", which essentially meant programming without the use of [[GOTO]].  Nearly all programmers now agree that, even in languages that provide GOTO, it is bad [[programming style|style]] to use it except in rare circumstances.
+The 1960s and 1970s also saw considerable debate over the merits of "[[structured programming]]", which essentially meant programming without the use of [[GOTO]].{{fact}}  Nearly all programmers now agree that, even in languages that provide GOTO, it is bad [[programming style|style]] to use it except in rare circumstances.{{fact}}
 === Consolidation and growth ===
-The 1980s were years of relative consolidation.  [[C_Plus_Plus|C++]] combined object-oriented and systems programming.  The United States government standardized [[Ada programming language|Ada]], a systems programming language intended for use by defense contractors.  In Japan and elsewhere, vast sums were spent investigating so-called "fifth generation" languages that incorporated logic programming constructs.  The functional languages community moved to standardize ML and Lisp.  Rather than inventing new paradigms, all of these movements elaborated upon the ideas invented in the previous decade.
+The 1980s were years of relative consolidation.  [[C_Plus_Plus|C++]] combined object-oriented and systems programming.{{fact}}  The United States government standardized [[Ada programming language|Ada]], a systems programming language intended for use by defense contractors.{{fact}}  In Japan and elsewhere, vast sums were spent investigating so-called "fifth generation" languages that incorporated logic programming constructs.{{fact}}  The functional languages community moved to standardize ML and Lisp.{{fact}}  Rather than inventing new paradigms, all of these movements elaborated upon the ideas invented in the previous decade.
-One important trend in language design during the 1980s was an increased focus on programming for large-scale systems through the use of ''modules'', or large-scale organizational units of code.  [[Modula-3]], Ada, and ML all developed notable module systems in the 1980s.  Module systems were often wedded to [[generic programming]] constructs.
+One important trend in language design during the 1980s was an increased focus on programming for large-scale systems through the use of ''modules'', or large-scale organizational units of code.{{fact}}  [[Modula-3]], Ada, and ML all developed notable module systems in the 1980s.{{fact}}  Module systems were often wedded to [[generic programming]] constructs.{{fact}}
-The rapid growth of the [[Internet]] in the mid-1990's created an opportunity for new languages to be adopted.  In particular, the [[Java programming language]] rose to popularity because of its early integration with [[web browser]]s, and various [[scripting language]]s achieved widespread use in developing customized applications for [[web server]]s.  Neither of these developments represented much fundamental novelty in language design, merely refinements in existing languages and paradigms.
+The rapid growth of the [[Internet]] in the mid-1990's created an opportunity for new languages to be adopted.  In particular, the [[Java programming language]] rose to popularity because of its early integration with [[web browser]]s,{{fact}} and various [[scripting language]]s achieved widespread use in developing customized applications for [[web server]]s.{{fact}}  Neither of these developments represented much fundamental novelty in language design, merely refinements in existing languages and paradigms.
-Programming language evolution continues, in both industry and research.  Current directions include mechanisms for adding security and reliability verification, alternative mechanisms for modularity ([[mixin]]s, [[delegation|delegates]], [[aspect-oriented programming|aspects]]), integration with databases, and a focus on [[open source]] as a developmental philosophy.
+Programming language evolution continues, in both industry and research.  Current directions include mechanisms for adding security and reliability verification,{{fact}} alternative mechanisms for modularity ([[mixin]]s,{{fact}} [[delegation|delegates]],{{fact}} [[aspect-oriented programming|aspects]]{{fact}}), integration with databases,{{fact}} and a focus on [[open source]] as a developmental philosophy.{{fact}}
 == Taxonomies ==
 {{main|Categorical list of programming languages}}
-There is no overarching classification scheme for programming languages.  Any given programming language does not usually have a single ancestor language.  Languages commonly arise by combining the elements of several predecessor languages with new ideas in circulation at the time.  Ideas that originate in one language will diffuse throughout a family of related languages, and then leap suddenly across familial gaps to appear in an entirely different family.
+There is no overarching classification scheme for programming languages.  Any given programming language does not usually have a single ancestor language.  Languages commonly arise by combining the elements of several predecessor languages with new ideas in circulation at the time.{{fact}}  Ideas that originate in one language will diffuse throughout a family of related languages, and then leap suddenly across familial gaps to appear in an entirely different family.
-The task is further complicated by the fact that languages can be classified along multiple axes.  For example, Java is both an object-oriented language (because it encourages object-oriented organization) and a concurrent language (because it contains built-in constructs for running multiple [[thread]]s in parallel).  [[Python programming language|Python]] is an object-oriented [[scripting language]].
+The task is further complicated by the fact that languages can be classified along multiple axes.  For example, Java is both an object-oriented language (because it encourages object-oriented organization){{fact}} and a concurrent language (because it contains built-in constructs for running multiple [[thread]]s in parallel).{{fact}}  [[Python programming language|Python]] is an object-oriented [[scripting language]].{{fact}}
-In broad strokes, programming languages divide into ''[[programming paradigm]]s'' and a classification by ''intended domain of use''.  Paradigms include [[procedural programming]], [[object-oriented programming]], [[functional programming]], and [[logic programming]]; some languages are hybrids of paradigms or multi-paradigmatic.  An [[assembly language]] is not so much a paradigm as a direct model of an underlying machine architecture.  By purpose, programming languages might be considered general purpose, system programming languages, scripting languages, domain-specific languages, or concurrent/distributed languages (or a combination of these).  Some general purpose languages were designed largely with educational goals.
+In broad strokes, programming languages divide into ''[[programming paradigm]]s'' and a classification by ''intended domain of use''.  Paradigms include [[procedural programming]], [[object-oriented programming]], [[functional programming]], and [[logic programming]];{{fact}} some languages are hybrids of paradigms or multi-paradigmatic.{{fact}}  An [[assembly language]] is not so much a paradigm as a direct model of an underlying machine architecture.{{fact}}  By purpose, programming languages might be considered general purpose, system programming languages, scripting languages, domain-specific languages, or concurrent/distributed languages (or a combination of these).  Some general purpose languages were designed largely with educational goals.{{fact}}
 ==See also==