What programming language is word written in

Vocabulary

1. Match the words with their definitions:

Before
you read

1. Discuss with your partner the following questions.

• What
  do you know about programming languages and paradigms?

• Is there any difference? Which one if any?

• What
  are the reasons for using programming languages and paradigms?
  

1. Skim the text to check your ideas.

READING

What is what?

I
n
this article, we will discuss programming languages and paradigms so
that you have a complete understanding. Let us first inspect if
there any difference is.

The
difference between programming paradigms and programming languages
is that programming language
is an artificial language that has vocabulary and sets of
grammatical rules to instruct a computer to perform specific tasks.
Programing paradigm
is a particular way (i.e., a ‘school of
thought’) of looking at a programming problem.

T
he
term programming language
usually refers to high-level languages, such as BASIC, C, C++,
COBOL, FORTRAN, Ada, and Pascal. Each language has a unique set of
keywords (words that it understands) and a special syntax
for organizing program instructions.
High-level programming languages, while simple compared to human
languages, are more complex than the languages the computer actually
understands, called machine languages.
Each different type of CPU has its own unique machine language.
Assembly languages
are lying between machine languages and high-level languages.
Assembly languages are similar to machine languages, but they are
much easier to program in because they allow a programmer to
substitute names for numbers. Machine languages consist of numbers
only. Lying above high-level languages are languages called
fourth-generation languages
(usually abbreviated 4GL).
4GLs are far removed from machine languages and represent the class
of computer languages closest to human languages. Regardless of what
language you use, you eventually need to convert your program into
machine language so that the computer can understand it. There are
two ways to do this: compile
the program and interpret
the program. A program that executes instructions is
written in a high-level language.
There are two ways to run programs written in a high-level language.
The most common is to compile the program. To transform a program
written in a high-level programming language from source
code into object
code. Programmers write programs in a form
called source code. Source code must go through several steps before
it becomes an executable program. The first step is to pass the
source code through a compiler,
which translates the high-level language instructions into object
code. The final step in producing an executable program — after the
compiler has produced object code — is to pass the object code
through a linker.
The linker combines modules and gives real values to all symbolic
addresses, thereby producing machine code.

The
other method is to pass the program through an interpreter. An
interpreter translates high-level instructions into an intermediate
form, which it then executes. In contrast, a compiler translates
high-level instructions directly into machine language. Compiled
programs generally run faster than interpreted programs. The
advantage of an interpreter, however, is that it does not need to go
through the compilation stage during which machine instructions are
generated. This process can be time-consuming if the program is
long. The interpreter, on the other hand, can immediately execute
high-level programs. For this reason, interpreters are sometimes
used during the development of a program, when a programmer wants to
add small sections at a time and test them quickly. In addition,
interpreters are often used in education because they allow students
to program interactively. Both interpreters and compilers are
available for most high-level languages. However, BASIC and LISP are
especially designed to be executed by an interpreter. In addition,
page description languages, such as PostScript, use an interpreter.
Every PostScript printer, for example, has a built-in interpreter
that executes PostScript instructions. The question of which
language is best is one that consumes a lot of time and energy among
computer professionals. Every language has its strengths and
weaknesses. For example, FORTRAN is a particularly good language for
processing numerical data, but it does not lend itself very well to
organizing large programs. Pascal is very good for writing
well-structured and readable programs, but it is not as flexible as
the C programming language. C++ embodies
powerful object-oriented features, but it is complex and difficult
to learn. The choice of which language to use depends on the type of
computer the program is to run
on, what sort of program it is, and the expertise of the programmer.
Computer programmers have evolved from the early days of the bit
processing first generation languages into sophisticated logical
designers of complex software applications. Programming is a rich
discipline and practical programming languages are usually quite
complicated. Fortunately, the important ideas of programming
languages are simple.

Adapted
from http://www.info.ucl.ac.be/~pvr/paradigms.htm

Usually,
the word «paradigm» is used to describe a thought pattern
or methodology that exists during a certain period of time. When
scientists refer to a scientific paradigm, they are talking about
the prevailing system of ideas that was dominant in a scientific
field at a point in time. When a person or field has a paradigm
shift,
it means that they are no longer using the old methods of thought
and approach, but have decided on a new approach, often reached
through an epiphany.

Programming
paradigm is a framework that defines how
the user conceptualized and interprets complex problems. It is also
is a fundamental style or the logical
approach to programming a computer based on a mathematical theory or
a coherent set of principles used in software engineering to
implement a programming language. There
are currently 27 paradigms (see the chart above) exist in the world.
Most of them are of similar concepts extending from the 4 main
programming paradigms.

P
rogramming
languages should support many paradigms. Let
us name 4 main programming paradigms: the
imperative paradigm,
the
functional paradigm,
the
logical paradigm,
the
object-oriented paradigm.
Other possible programming paradigms are: the visual paradigm, one
of the parallel/
concurrent paradigms
and the constraint
based
paradigm. The
paradigms are not exclusive, but reflect the different emphasis of
language designers. Most practical languages embody features of more
than one paradigm.

Each
paradigm supports a set of concepts that makes it the best for a
certain kind of problem. For example, object-oriented programming is
best for problems with a large number of related data abstractions
organized in a hierarchy. Logic programming is best for transforming
or navigating complex symbolic structures according to logical
rules. Discrete synchronous programming is best for reactive
problems, i.e., problems that consist of reactions to sequences of
external events. Programming
paradigms are unique to each language within the computer
programming domain, and many programming
languages utilize multiple paradigms. The term paradigm
is best described as a «pattern or model.» Therefore, a
programming
paradigm
can be defined as a pattern or model used within a software
programming
language to create software applications. Languages that support
these three paradigms are given in a classification table below.

Popular
mainstream languages such as Java or C++ support just one or two
separate paradigms. This is unfortunate, since different programming
problems need different programming concepts to solve them cleanly,
and those one or two paradigms often do not contain the right
concepts. A language should ideally support many concepts in a
well-factored way, so that the programmer can choose the right
concepts whenever they are needed without being encumbered
by the others. This style of programming is sometimes called
multiparadigm programming, implying that it is something exotic and
out of the ordinary.

Programming
languages are extremely logical and follow standard rules of
mathematics. Each language has a unique method for applying these
rules, especially around the areas of functions, variables, methods,
and objects. For example, programs written in C++ or Object Pascal
can be purely procedural, or purely object-oriented, or contain
elements of both paradigms. Software designers and programmers
decide how to use those paradigm elements. In object-oriented
programming, programmers can think of a program as a collection of
interacting objects, while in functional programming a program can
be thought of as a sequence of stateless function evaluations. When
programming computers or systems with many processors,
process-oriented programming allows programmers to think about
applications as sets of concurrent
processes acting upon logically shared data structures. Just as
different groups in software engineering advocate different
methodologies,
different programming languages advocate different programming
paradigms.
Some languages are designed to support one particular paradigm
(Smalltalk supports object-oriented programming, Haskell supports
functional programming), while other programming languages support
multiple paradigms (such as Object Pascal, C++, C#, Visual Basic,
Common Lisp, Scheme, Perl, Python, Ruby, Oz and F Sharp).

It
is helpful to understand the history of the programming
language and software in general to better grasp the concept of the
programming
paradigm. In the
early days of software development, software engineering was
completed by creating binary code or machine code, represented by 1s
and 0s. These binary manipulations caused programs to react in a
specified manner. This early computer programming is commonly
referred to as the «low-level» programming
paradigm. This
was a tedious and error prone
method for creating programs. Programming
languages quickly evolved into the «procedural» paradigm
or third generation languages including COBOL, Fortran, and BASIC.
These procedural programming languages define programs in a
step-by-step approach.

The
next evolution of programming
languages was to create a more logical approach to software
development, the «object oriented» programming
paradigm. This
approach is used by the programming
languages of Java™, Smalltalk, and Eiffel. This paradigm
attempts to abstract modules of a program into reusable objects.

In
addition to these programming
paradigms, there is also the «declarative» paradigm
and the «functional» paradigm.
While some programming
languages strictly enforce the use of a single paradigm,
many support multiple paradigms. Some examples of these types
include C++, C#, and Visual Basic®.

Each
paradigm
has unique requirements on the usage and abstractions of processes
within the programming
language. Nevertheless, Peter Van Roy says that understanding the
right concepts can help improve programming style even in languages
that do not directly support them, just as object-oriented
programming is possible in C with the right programmer attitude.

By
allowing developers flexibility within programming
languages, a programming
paradigm can be
utilized that best meets the business problem to be solved. As the
art of computer programming
has evolved, so too has the creation of the programming
paradigm. By
creating a framework of a pattern or model for system development,
programmers can create computer programs to be the most efficiency
within the selected paradigm.

LANGUAGE
DEVELOPMENT

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A programming language is a system of notation for writing computer programs.^[1] Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language.

The description of a programming language is usually split into the two components of syntax (form) and semantics (meaning), which are usually defined by a formal language. Some languages are defined by a specification document (for example, the C programming language is specified by an ISO Standard) while other languages (such as Perl) have a dominant implementation that is treated as a reference. Some languages have both, with the basic language defined by a standard and extensions taken from the dominant implementation being common.

Programming language theory is the subfield of computer science that studies the design, implementation, analysis, characterization, and classification of programming languages.

Definitions[edit]

There are many considerations when defining what constitutes a programming language.

Computer languages vs programming languages[edit]

The term computer language is sometimes used interchangeably with programming language.^[2] However, the usage of both terms varies among authors, including the exact scope of each. One usage describes programming languages as a subset of computer languages.^[3] Similarly, languages used in computing that have a different goal than expressing computer programs are generically designated computer languages. For instance, markup languages are sometimes referred to as computer languages to emphasize that they are not meant to be used for programming.^[4]
One way of classifying computer languages is by the computations they are capable of expressing, as described by the theory of computation. The majority of practical programming languages are Turing complete,^[5] and all Turing complete languages can implement the same set of algorithms. ANSI/ISO SQL-92 and Charity are examples of languages that are not Turing complete, yet are often called programming languages.^[6][7] However, some authors restrict the term «programming language» to Turing complete languages.^[1][8]

Another usage regards programming languages as theoretical constructs for programming abstract machines and computer languages as the subset thereof that runs on physical computers, which have finite hardware resources.^[9] John C. Reynolds emphasizes that formal specification languages are just as much programming languages as are the languages intended for execution. He also argues that textual and even graphical input formats that affect the behavior of a computer are programming languages, despite the fact they are commonly not Turing-complete, and remarks that ignorance of programming language concepts is the reason for many flaws in input formats.^[10]

Domain and target[edit]

In most practical contexts, a programming language involves a computer; consequently, programming languages are usually defined and studied this way.^[11] 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.

The domain of the language is also worth consideration. Markup languages like XML, HTML, or troff, which define structured data, are not usually considered programming languages.^[12][13][14] Programming languages may, however, share the syntax with markup languages if a computational semantics is defined. XSLT, for example, is a Turing complete language entirely using XML syntax.^[15][16][17] Moreover, LaTeX, which is mostly used for structuring documents, also contains a Turing complete subset.^[18][19]

Abstractions[edit]

Programming languages usually contain abstractions for defining and manipulating data structures or controlling the flow of execution. The practical necessity that a programming language support adequate abstractions is expressed by the abstraction principle.^[20] This principle is sometimes formulated as a recommendation to the programmer to make proper use of such abstractions.^[21]

History[edit]

Early developments[edit]

Very early computers, such as Colossus, were programmed without the help of a stored program, by modifying their circuitry or setting banks of physical controls.

Slightly later, programs could be written in machine language, where the programmer writes each instruction in a numeric form the hardware can execute directly. For example, the instruction to add the value in two memory locations might consist of 3 numbers: an «opcode» that selects the «add» operation, and two memory locations. The programs, in decimal or binary form, were read in from punched cards, paper tape, magnetic tape or toggled in on switches on the front panel of the computer. Machine languages were later termed first-generation programming languages (1GL).

The next step was the development of the so-called second-generation programming languages (2GL) or assembly languages, which were still closely tied to the instruction set architecture of the specific computer. These served to make the program much more human-readable and relieved the programmer of tedious and error-prone address calculations.

The first high-level programming languages, or third-generation programming languages (3GL), were written in the 1950s. An early high-level programming language to be designed for a computer was Plankalkül, developed for the German Z3 by Konrad Zuse between 1943 and 1945. However, it was not implemented until 1998 and 2000.^[22]

John Mauchly’s Short Code, proposed in 1949, was one of the first high-level languages ever developed for an electronic computer.^[23] Unlike machine code, Short Code statements represented mathematical expressions in an understandable form. However, the program had to be translated into machine code every time it ran, making the process much slower than running the equivalent machine code.

At the University of Manchester, Alick Glennie developed Autocode in the early 1950s. As a programming language, it used a compiler to automatically convert the language into machine code. The first code and compiler was developed in 1952 for the Mark 1 computer at the University of Manchester and is considered to be the first compiled high-level programming language.^[24][25]

The second auto code was developed for the Mark 1 by R. A. Brooker in 1954 and was called the «Mark 1 Autocode». Brooker also developed an auto code for the Ferranti Mercury in the 1950s in conjunction with the University of Manchester. The version for the EDSAC 2 was devised by D. F. Hartley of University of Cambridge Mathematical Laboratory in 1961. Known as EDSAC 2 Autocode, it was a straight development from Mercury Autocode adapted for local circumstances and was noted for its object code optimization and source-language diagnostics which were advanced for the time. A contemporary but separate thread of development, Atlas Autocode was developed for the University of Manchester Atlas 1 machine.

In 1954, FORTRAN was invented at IBM by John Backus. It was the first widely used high-level general-purpose programming language to have a functional implementation, as opposed to just a design on paper.^[26][27] It is still a popular language for high-performance computing^[28] and is used for programs that benchmark and rank the world’s fastest supercomputers.^[29]

Another early programming language was devised by Grace Hopper in the US, called FLOW-MATIC. It was developed for the UNIVAC I at Remington Rand during the period from 1955 until 1959. Hopper found that business data processing customers were uncomfortable with mathematical notation, and in early 1955, she and her team wrote a specification for an English programming language and implemented a prototype.^[30] The FLOW-MATIC compiler became publicly available in early 1958 and was substantially complete in 1959.^[31] FLOW-MATIC was a major influence in the design of COBOL, since only it and its direct descendant AIMACO were in actual use at the time.^[32]

Refinement[edit]

The increased use of high-level languages introduced a requirement for low-level programming languages or system programming languages. These languages, to varying degrees, provide facilities between assembly languages and high-level languages. They can be used to perform tasks that require direct access to hardware facilities but still provide higher-level control structures and error-checking.

The period from the 1960s to the late 1970s brought the development of the major language paradigms now in use:

• APL introduced array programming and influenced functional programming.^[33]
• ALGOL refined both structured procedural programming and the discipline of language specification; the «Revised Report on the Algorithmic Language ALGOL 60» became a model for how later language specifications were written.
• Lisp, implemented in 1958, was the first dynamically-typed functional programming language.
• In the 1960s, Simula was the first language designed to support object-oriented programming; in the mid-1970s, Smalltalk followed with the first «purely» object-oriented language.
• C was developed between 1969 and 1973 as a system programming language for the Unix operating system and remains popular.^[34]
• Prolog, designed in 1972, was the first logic programming language.
• In 1978, ML built a polymorphic type system on top of Lisp, pioneering statically-typed functional programming languages.

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

The 1960s and 1970s also saw considerable debate over the merits of structured programming, and whether programming languages should be designed to support it.^[35] Edsger Dijkstra, in a famous 1968 letter published in the Communications of the ACM, argued that Goto statements should be eliminated from all «higher-level» programming languages.^[36]

Consolidation and growth[edit]

The 1980s were years of relative consolidation. C++ combined object-oriented and systems programming. The United States government standardized Ada, a systems programming language derived from Pascal and intended for use by defense contractors. In Japan and elsewhere, vast sums were spent investigating the so-called «fifth-generation» languages that incorporated logic programming constructs.^[37] 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 decades.

One important trend in language design for programming large-scale systems during the 1980s was an increased focus on the use of modules or large-scale organizational units of code. Modula-2, Ada, and ML all developed notable module systems in the 1980s, which were often wedded to generic programming constructs.^[38]

The rapid growth of the Internet in the mid-1990s created opportunities for new languages. Perl, originally a Unix scripting tool first released in 1987, became common in dynamic websites. Java came to be used for server-side programming, and bytecode virtual machines became popular again in commercial settings with their promise of «Write once, run anywhere» (UCSD Pascal had been popular for a time in the early 1980s). These developments were not fundamentally novel; rather, they were refinements of many existing languages and paradigms (although their syntax was often based on the C family of programming languages).

Programming language evolution continues, in both industry and research. Current directions include security and reliability verification, new kinds of modularity (mixins, delegates, aspects), and database integration such as Microsoft’s LINQ.

Fourth-generation programming languages (4GL) are computer programming languages that aim to provide a higher level of abstraction of the internal computer hardware details than 3GLs. Fifth-generation programming languages (5GL) are programming languages based on solving problems using constraints given to the program, rather than using an algorithm written by a programmer.

Elements[edit]

All programming languages have some primitive building blocks for the description of data and the processes or transformations applied to them (like the addition of two numbers or the selection of an item from a collection). These primitives are defined by syntactic and semantic rules which describe their structure and meaning respectively.

Syntax[edit]

A programming language’s surface form is known as its syntax. Most programming languages are purely textual; they use sequences of text including words, numbers, and punctuation, much like written natural languages. On the other hand, some programming languages are more graphical in nature, using visual relationships between symbols to specify a program.

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 (either formal or hard-coded in a reference implementation). Since most languages are textual, this article discusses textual syntax.

The programming language syntax is usually defined using a combination of regular expressions (for lexical structure) and Backus–Naur form (for grammatical structure). 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 the following:

• an expression is either an atom or a list;
• an atom is either a number or a symbol;
• a number is an unbroken sequence of one or more decimal digits, optionally preceded by a plus or minus sign;
• a symbol is a letter followed by zero or more of any characters (excluding whitespace); and
• a list is a matched pair of parentheses, with zero or more expressions inside it.

The following are examples of well-formed token sequences in this grammar: 12345, () and (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. 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 operations that are not semantically defined (the operation *p >> 4 has no meaning for a value having a complex type and p->im is not defined because the value of p is the null pointer):

complex *p = NULL;
complex abs_p = sqrt(*p >> 4 + p->im);

If the type declaration on the first line were omitted, the program would trigger an error on the undefined variable p during compilation. However, the program would still be syntactically correct since type declarations provide only semantic information.

The grammar needed to specify a programming language can be classified by its position in the Chomsky hierarchy. The syntax of most programming languages can be specified using a Type-2 grammar, i.e., they are context-free grammars.^[39] Some languages, including Perl and Lisp, contain constructs that allow execution during the parsing phase. Languages that have constructs that allow the programmer to alter the behavior of the parser make syntax analysis an undecidable problem, and generally blur the distinction between parsing and execution.^[40] In contrast to Lisp’s macro system and Perl’s BEGIN blocks, which may contain general computations, C macros are merely string replacements and do not require code execution.^[41]

Semantics[edit]

The term semantics refers to the meaning of languages, as opposed to their form (syntax).

Static semantics[edit]

A static semantics defines restrictions on the structure of valid texts that are hard or impossible to express in standard syntactic formalisms.^{[1][failed verification]} For compiled languages, static semantics essentially include those semantic rules that can be checked at compile time. Examples include checking that every identifier is declared before it is used (in languages that require such declarations) or that the labels on the arms of a case statement are distinct.^[42] Many important restrictions of this type, like checking that identifiers are used in the appropriate context (e.g. not adding an integer to a function name), or that subroutine calls have the appropriate number and type of arguments, can be enforced by defining them as rules in a logic called a type system. Other forms of static analyses like data flow analysis may also be part of static semantics. Newer programming languages like Java and C# have definite assignment analysis, a form of data flow analysis, as part of their static semantics.

Dynamic semantics[edit]

Once data has been specified, the machine must be instructed to perform operations on the data. 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. The dynamic semantics (also known as execution semantics) of a language defines how and when the various constructs of a language should produce a program behavior. There are many ways of defining execution semantics. Natural language is often used to specify the execution semantics of languages commonly used in practice. A significant amount of academic research went into formal semantics of programming languages, which allows execution semantics to be specified in a formal manner. Results from this field of research have seen limited application to programming language design and implementation outside academia.

Type system[edit]

A type system defines how a programming language classifies values and expressions into types, how it can manipulate those types and how they interact. The goal of a type system is to verify and usually enforce a certain level of correctness in programs written in that language by detecting certain incorrect operations. Any decidable type system involves a trade-off: while it rejects many incorrect programs, it can also prohibit some correct, albeit unusual programs. In order to bypass this downside, a number of languages have type loopholes, usually unchecked casts that may be used by the programmer to explicitly allow a normally disallowed operation between different types. In most typed languages, the type system is used only to type check programs, but a number of languages, usually functional ones, infer types, relieving the programmer from the need to write type annotations. The formal design and study of type systems is known as type theory.

Typed versus untyped languages[edit]

A language is typed if the specification of every operation defines types of data to which the operation is applicable.^[43] For example, the data represented by "this text between the quotes" is a string, and in many programming languages dividing a number by a string has no meaning and will not be executed. The invalid operation may be detected when the program is compiled («static» type checking) and will be rejected by the compiler with a compilation error message, or it may be detected while the program is running («dynamic» type checking), resulting in a run-time exception. Many languages allow a function called an exception handler to handle this exception and, for example, always return «-1» as the result.

A special case of typed languages is the single-typed languages. These are often scripting or markup languages, such as REXX or SGML, and have only one data type^{[dubious – discuss]}–—most commonly character strings which are used for both symbolic and numeric data.

In contrast, an untyped language, such as most assembly languages, allows any operation to be performed on any data, generally sequences of bits of various lengths.^[43] High-level untyped languages include BCPL, Tcl, and some varieties of Forth.

In practice, while few languages are considered typed from the type theory (verifying or rejecting all operations), most modern languages offer a degree of typing.^[43] Many production languages provide means to bypass or subvert the type system, trading type safety for finer control over the program’s execution (see casting).

Static vis-à-vis dynamic typing[edit]

In static typing, all expressions have their types determined prior to when the program is executed, typically 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.^[43]

Statically-typed languages can be either manifestly typed or type-inferred. In the first case, the programmer must explicitly write types at certain textual positions (for example, at variable declarations). In the second case, the compiler infers the types of expressions and declarations based on context. Most mainstream statically-typed languages, such as C++, C# and Java, are manifestly typed. Complete type inference has traditionally been associated with functional languages such as Haskell and ML.^[44] However, many manifestly-typed languages support partial type inference; for example, C++, Java, and C# all infer types in certain limited cases.^[45] Additionally, some programming languages allow for some types to be automatically converted to other types; for example, an int can be used where the program expects a float.

Dynamic typing, also called latent typing, determines the type-safety of operations at run time; in other words, types are associated with run-time values rather than textual expressions.^[43] 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, potentially making debugging more difficult. Lisp, Smalltalk, Perl, Python, JavaScript, and Ruby are all examples of dynamically-typed languages.

Weak and strong typing[edit]

Weak typing allows a value of one type to be treated as another, for example treating a string as a number.^[43] This can occasionally be useful, but it can also allow some kinds of program faults to go undetected at compile time and even at run time.

Strong typing prevents these program faults. An attempt to perform an operation on the wrong type of value raises an error.^[43] Strongly-typed languages are often termed type-safe or safe.

An alternative definition for «weakly typed» refers to languages, such as Perl and JavaScript, which permit a large number of implicit type conversions. In JavaScript, for example, the expression 2 * x implicitly converts x to a number, and this conversion succeeds even if x is null, undefined, an Array, or a string of letters. Such implicit conversions are often useful, but they can mask programming errors. Strong and static are now 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 both strongly typed and weakly, statically typed.^[46][47]

It may seem odd to some professional programmers that C could be «weakly, statically typed». However, the use of the generic pointer, the void* pointer, does allow casting pointers to other pointers without needing to do an explicit cast. This is extremely similar to somehow casting an array of bytes to any kind of datatype in C without using an explicit cast, such as (int) or (char).

Standard library and run-time system[edit]

Most programming languages have an associated core library (sometimes known as the «standard library», especially if it is included as part of the published language standard), which is conventionally made available by all implementations of the language. Core libraries typically include definitions for commonly used algorithms, data structures, and mechanisms for input and output.

The line between a language and its core library differs from language to language. In some cases, the language designers may treat the library as a separate entity from the language. However, a language’s core library is often treated as part of the language by its users, and some language specifications even require that this library be made available in all implementations. Indeed, some languages are designed so that the meanings of certain syntactic constructs cannot even be described without referring to the core library. For example, in Java, a string literal is defined as an instance of the java.lang.String class; similarly, in Smalltalk, an anonymous function expression (a «block») constructs an instance of the library’s BlockContext class. 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 a library.

Design and implementation[edit]

Programming languages share properties with natural languages related to their purpose as vehicles for communication, having a syntactic form separate from its semantics, and showing language families of related languages branching one from another.^[48][49] But as artificial constructs, they also differ in fundamental ways from languages that have evolved through usage. A significant difference is that a programming language can be fully described and studied in its entirety since it has a precise and finite definition.^[50] By contrast, natural languages have changing meanings given by their users in different communities. While constructed languages are also artificial languages designed from the ground up with a specific purpose, they lack the precise and complete semantic definition that a programming language has.

Many programming languages have been designed from scratch, altered to meet new needs, and combined with other languages. Many have eventually fallen into disuse. Although there have been attempts to design one «universal» programming language that serves all purposes, all of them have failed to be generally accepted as filling this role.^[51] The need for diverse programming 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 must balance speed, size, and simplicity on systems ranging from microcontrollers to supercomputers.
• Programs may be written once and not change for generations, or they may undergo continual modification.
• Programmers may simply differ in their tastes: 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 remote from simple translation into underlying hardware instructions. Because programmers are less tied to the complexity of the computer, their programs can do more computing with less effort from the programmer. This lets them write more functionality per time unit.^[52]

Natural-language programming has 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 W. 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».^[53] Alan Perlis was similarly dismissive of the idea.^[54] Hybrid approaches have been taken in Structured English and SQL.

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 specification and implementation.

Specification[edit]

The specification of a programming language is an artifact that the language users and the implementors can use to agree upon whether a piece of source code is a valid program in that language, and if so what its behavior shall be.

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

• An explicit definition of the syntax, static semantics, and execution semantics of the language. While syntax is commonly specified using a formal grammar, semantic definitions may be written in natural language (e.g., as in the C language), or a formal semantics (e.g., as in Standard ML^[55] and Scheme^[56] specifications).
• A description of the behavior of a translator for the language (e.g., the C++ and Fortran specifications). The syntax and semantics of the language have to be inferred from this description, which may be written in natural or formal language.
• A reference or model implementation, sometimes written in the language being specified (e.g., Prolog or ANSI REXX^[57]). The syntax and semantics of the language are explicit in the behavior of the reference implementation.

Implementation[edit]

An implementation of a programming language provides a way to write programs in that language and execute them on one or more configurations of hardware and software. There are, broadly, two approaches to programming language implementation: compilation and interpretation. It is generally possible to implement a language using either technique.

The output of a compiler may be executed by hardware or a program called an interpreter. In some implementations that make use of the interpreter approach, there is no distinct boundary between compiling and interpreting. For instance, some implementations of BASIC compile and then execute the source one line at a time.

Programs that are executed directly on the hardware usually run much faster than those that are interpreted in software.^{[58][better source needed]}

One technique for improving the performance of interpreted programs is just-in-time compilation. Here the virtual machine, just before execution, translates the blocks of bytecode which are going to be used to machine code, for direct execution on the hardware.

Proprietary languages[edit]

Although most of the most commonly used programming languages have fully open specifications and implementations, many programming languages exist only as proprietary programming languages with the implementation available only from a single vendor, which may claim that such a proprietary language is their intellectual property. Proprietary programming languages are commonly domain-specific languages or internal scripting languages for a single product; some proprietary languages are used only internally within a vendor, while others are available to external users.

Some programming languages exist on the border between proprietary and open; for example, Oracle Corporation asserts proprietary rights to some aspects of the Java programming language,^[59] and Microsoft’s C# programming language, which has open implementations of most parts of the system, also has Common Language Runtime (CLR) as a closed environment.^[60]

Many proprietary languages are widely used, in spite of their proprietary nature; examples include MATLAB, VBScript, and Wolfram Language. Some languages may make the transition from closed to open; for example, Erlang was originally Ericsson’s internal programming language.^[61]

Use[edit]

Thousands of different programming languages have been created, mainly in the computing field.^[62]
Individual software projects commonly use five programming languages or more.^[63]

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 to communicate with other people, human authors and speakers can be ambiguous and make small errors, and still expect their intent to be understood. However, figuratively speaking, computers «do exactly what they are told to do», and cannot «understand» what code the programmer intended to write. The combination of the language definition, a program, and the program’s inputs must fully specify the external behavior that occurs when the program is executed, within the domain of control of that program. On the other hand, ideas about an algorithm can be communicated to humans without the precision required for execution by using pseudocode, which interleaves natural language with code written in a programming language.

A programming language provides a structured mechanism for defining pieces of data, and the operations or transformations that may be carried out automatically on that data. A programmer uses the abstractions present in the language to represent the concepts involved in a computation. These concepts are represented as a collection of the simplest elements available (called primitives).^[64] Programming is the process by which programmers combine these primitives to compose new programs, or adapt existing ones to new uses or a changing environment.

Programs for a computer might be executed in a batch process without human interaction, or a user might type commands in an interactive session of an interpreter. In this case the «commands» are simply programs, whose execution is chained together. When a language can run its commands through an interpreter (such as a Unix shell or other command-line interface), without compiling, it is called a scripting language.^[65]

Measuring language usage[edit]

Determining which is the most widely used programming language is difficult since the definition of usage varies by context. One language may occupy the greater number of programmer hours, a different one has more lines of code, and a third may consume the most CPU time. Some languages are very popular for particular kinds of applications. For example, COBOL is still strong in the corporate data center, often on large mainframes;^[66][67] Fortran in scientific and engineering applications; Ada in aerospace, transportation, military, real-time, and embedded applications; and C in embedded applications and operating systems. Other languages are regularly used to write many different kinds of applications.

Various methods of measuring language popularity, each subject to a different bias over what is measured, have been proposed:

• counting the number of job advertisements that mention the language^[68]
• the number of books sold that teach or describe the language^[69]
• estimates of the number of existing lines of code written in the language – which may underestimate languages not often found in public searches^[70]
• counts of language references (i.e., to the name of the language) found using a web search engine.

Combining and averaging information from various internet sites, stackify.com reported the ten most popular programming languages (in descending order by overall popularity): Java, C, C++, Python, C#, JavaScript, VB .NET, R, PHP, and MATLAB.^[71]

Dialects, flavors and implementations[edit]

A dialect of a programming language or a data exchange language is a (relatively small) variation or extension of the language that does not change its intrinsic nature. With languages such as Scheme and Forth, standards may be considered insufficient, inadequate, or illegitimate by implementors, so often they will deviate from the standard, making a new dialect. In other cases, a dialect is created for use in a domain-specific language, often a subset. In the Lisp world, most languages that use basic S-expression syntax and Lisp-like semantics are considered Lisp dialects, although they vary wildly, as do, say, Racket and Clojure. As it is common for one language to have several dialects, it can become quite difficult for an inexperienced programmer to find the right documentation. The BASIC programming language has many dialects.

Taxonomies[edit]

There is no overarching classification scheme for programming languages. A 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.

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 threads in parallel). Python is an object-oriented scripting language.^[72]

In broad strokes, programming languages are classified by programming paradigm and intended domain of use, with general-purpose programming languages distinguished from domain-specific programming languages. Traditionally, programming languages have been regarded as describing computation in terms of imperative sentences, i.e. issuing commands. These are generally called imperative programming languages. A great deal of research in programming languages has been aimed at blurring the distinction between a program as a set of instructions and a program as an assertion about the desired answer, which is the main feature of declarative programming.^[73] More refined 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).^[74] Some general purpose languages were designed largely with educational goals.^[75]

A programming language may also be classified by factors unrelated to the programming paradigm. For instance, most programming languages use English language keywords, while a minority do not. Other languages may be classified as being deliberately esoteric or not.

See also[edit]

References[edit]

Further reading[edit]

Examining the list of shared libraries (DLLs in Windows-speak) of a compiled program can give a clue, because typically each language has a specific distinctive library to provide the runtime environment.

For example, on my Linux PC, running the ldd command on an executable produced the following tell-tale output:

ldd *redacted*
    linux-gate.so.1 =>  (0x0042e000)
    libxerces-c.so.28 => /usr/local/lib/libxerces-c.so.28 (0x004b0000)
    *redacted*.so => not found
    libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x05f28000)
    libm.so.6 => /lib/libm.so.6 (0x00a61000)
    libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x05be0000)
    libc.so.6 => /lib/libc.so.6 (0x00906000)
    libpthread.so.0 => /lib/libpthread.so.0 (0x00a93000)
    /lib/ld-linux.so.2 (0x008e7000)

The use of libc.so suggests C or C++. The use of libstdc++.so suggests C++. In fact that was a C++ program.

Searching the program executable for human readable strings can also given clues, especially if it has debugging information present.

For example, running the strings command on that same executable revealled (among much other text) the following tell-tale strings:

virtual std::ostream* XmlToDcs::AmsResultsHandler::createOutputFileIfPossible()
pointer != static_cast< unsigned int >(-1)
std::ofstream* XmlToDcs::IndexElementsHandler::createStatementsFile(const tm&, char, char, unsigned int)
EamResultsHandler.cpp

The first three look like fragments of C++, the last looks like the name of a C++ source code file.

A programming language is a notation for writing

programs

, which are specifications of a computation or

algorithm

.

[2]

Some authors restrict the term «programming language» to those languages that can express all possible algorithms.

[2]

​

[3]

Traits often considered important for what constitutes a programming language include:Function and targetA computer programming language is a

language

used to write

computer programs

, which involves a

computer

performing some kind of computation

[4]

or

algorithm

and possibly control external devices such as

printers

,

disk drives

,

robots

,

[5]

and so on. For example,

PostScript

programs are frequently created by another program to control a computer printer or display. More generally, a programming language may describe computation on some, possibly abstract, machine. It is generally accepted that a complete specification for a programming language includes a description, possibly idealized, of a machine or processor for that language.

[6]

In most practical contexts, a programming language involves a computer; consequently, programming languages are usually defined and studied this way.

[7]

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.AbstractionsProgramming languages usually contain

abstractions

for defining and manipulating

data structures

or controlling the

flow of execution

. The practical necessity that a programming language support adequate abstractions is expressed by the

abstraction principle

.

[8]

This principle is sometimes formulated as a recommendation to the programmer to make proper use of such abstractions.

[9]

Expressive powerThe

theory of computation

classifies languages by the computations they are capable of expressing. All

Turing-complete

languages can implement the same set of

algorithms

.

ANSI/ISO SQL-92

and

Charity

are examples of languages that are not Turing complete, yet are often called programming languages.

[10]

​

[11]

​

Uses of wordsEdit

Word size choiceEdit

Size familiesEdit

Table of word sizesEdit

See alsoEdit

NotesEdit

ReferencesEdit