Misplaced Pages

#837162

90-420: The " current continuation " or "continuation of the computation step" is the continuation that, from the perspective of running code, would be derived from the current point in a program's execution. The term continuations can also be used to refer to first-class continuations , which are constructs that give a programming language the ability to save the execution state at any point and return to that point at

180-621: A Keynote Speech to the 1996 OOPSLA Convention. Here he reflected on how his work on Patterns in Architecture had developed and his hopes for how the Software Design community could help Architecture extend Patterns to create living structures that use generative schemes that are more like computer code. A pattern describes a design motif , a.k.a. prototypical micro-architecture , as a set of program constituents (e.g., classes, methods...) and their relationships. A developer adapts

270-406: A heap and automatic garbage collection . For the next decades, Lisp dominated artificial intelligence applications. In 1978, another functional language, ML , introduced inferred types and polymorphic parameters . After ALGOL (ALGOrithmic Language) was released in 1958 and 1960, it became the standard in computing literature for describing algorithms . Although its commercial success

360-400: A logic called a type system . Other forms of static analyses like data flow analysis may also be part of static semantics. Programming languages such as Java and C# have definite assignment analysis , a form of data flow analysis, as part of their respective static semantics. Once data has been specified, the machine must be instructed to perform operations on the data. For example,

450-495: A commonly used documentation format is the one used by Erich Gamma , Richard Helm , Ralph Johnson , and John Vlissides in their book Design Patterns . It contains the following sections: Some suggest that design patterns may be a sign that features are missing in a given programming language ( Java or C++ for instance). Peter Norvig demonstrates that 16 out of the 23 patterns in the Design Patterns book (which

540-543: A continuation may be invoked repeatedly (even after it has already returned). Re-invocable continuations were introduced by Peter J. Landin using his J (for Jump) operator that could transfer the flow of control back into the middle of a procedure invocation. Re-invocable continuations have also been called "re-entrant" in the Racket language. However this use of the term "re-entrant" can be easily confused with its use in discussions of multithreading . A more limited kind

630-447: A data type whose elements, in many languages, must consist of a single type of fixed length. Other languages define arrays as references to data stored elsewhere and support elements of varying types. Depending on the programming language, sequences of multiple characters, called strings , may be supported as arrays of characters or their own primitive type . Strings may be of fixed or variable length, which enables greater flexibility at

720-566: A design pattern describes the context in which the pattern is used, the forces within the context that the pattern seeks to resolve, and the suggested solution. There is no single, standard format for documenting design patterns. Rather, a variety of different formats have been used by different pattern authors. However, according to Martin Fowler , certain pattern forms have become more well-known than others, and consequently become common starting points for new pattern-writing efforts. One example of

810-444: A first-class continuation as saving the execution state of the program. True first-class continuations do not save program data – unlike a process image – only the execution context. This is illustrated by the "continuation sandwich" description: Say you're in the kitchen in front of the refrigerator, thinking about a sandwich. You take a continuation right there and stick it in your pocket. Then you get some turkey and bread out of

900-440: A gentler introduction to this mechanism, see call-with-current-continuation . This example shows a possible usage of continuations to implement coroutines as separate threads. The functions defined above allow for defining and executing threads through cooperative multitasking , i.e. threads that yield control to the next one in a queue: The previous code will produce this output: A program must allocate space in memory for

990-658: A later point in the program, possibly multiple times. The earliest description of continuations was made by Adriaan van Wijngaarden in September 1964. Wijngaarden spoke at the IFIP Working Conference on Formal Language Description Languages held in Baden bei Wien, Austria. As part of a formulation for an Algol 60 preprocessor, he called for a transformation of proper procedures into continuation-passing style , though he did not use this name, and his intention

SECTION 10

#1732773361838

1080-422: A meaning to a grammatically correct sentence or the sentence may be false: 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 ): If the type declaration on the first line were omitted,

1170-495: A model that lends itself very poorly to expressing computational problems. Thus continuations enable code that has the useful properties associated with inversion of control , while avoiding its problems. "Inverting back the inversion of control or, Continuations versus page-centric programming" is a paper that provides a good introduction to continuations applied to web programming. Support for continuations varies widely. A programming language supports re-invocable continuations if

1260-454: A performance cost. Programming language theory is the subfield of computer science that studies the design, implementation, analysis, characterization, and classification of programming languages. Programming languages differ from natural languages in that natural languages are used for interaction between people, while programming languages are designed to allow humans to communicate instructions to machines. The term computer language

1350-425: A programming language is required in order to execute programs, namely an interpreter or a compiler . An interpreter directly executes the source code, while a compiler produces an executable program. Computer architecture has strongly influenced the design of programming languages, with the most common type ( imperative languages —which implement operations in a specified order) developed to perform well on

1440-416: A sentence like "someone saw everyone" may be ambiguous between ∃ x ∀ y , saw ( x , y ) {\displaystyle \exists x\forall y,{\mbox{saw}}(x,y)} and ∀ y ∃ x , saw ( x , y ) {\displaystyle \forall y\exists x,{\mbox{saw}}(x,y)} ). He also observed that this idea

1530-483: A structured approach to computer programming . Conceptually, design pattern may be described as more specific than programming paradigm and less specific than algorithm . Patterns originated as an architectural concept by Christopher Alexander as early as 1977 in A Pattern Language (c.f. his article, "The Pattern of Streets," JOURNAL OF THE AIP, September, 1966, Vol. 32, No. 5, pp. 273–278). In 1987, Kent Beck and Ward Cunningham began experimenting with

1620-406: Is a set of allowable values and operations that can be performed on these values. Each programming language's type system defines which data types exist, the type of an expression , and how type equivalence and type compatibility function in the language. According to type theory , a language is fully typed if the specification of every operation defines types of data to which the operation

1710-464: Is a topic of current research. Programming language This is an accepted version of this page A programming language is a system of notation for writing computer programs . Programming languages are described in terms of their syntax (form) and semantics (meaning), usually defined by a formal language . Languages usually provide features such as a type system , variables , and mechanisms for error handling . An implementation of

1800-415: Is allowed, the fewer type errors can be detected. Early programming languages often supported only built-in, numeric types such as the integer (signed and unsigned) and floating point (to support operations on real numbers that are not integers). Most programming languages support multiple sizes of floats (often called float and double ) and integers depending on the size and precision required by

1890-419: Is applicable. 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. In practice, while few languages are fully typed, most offer a degree of typing. Because different types (such as integers and floats ) represent values differently, unexpected results will occur if one type is used when another

SECTION 20

#1732773361838

1980-469: Is expected. Type checking will flag this error, usually at compile time (runtime type checking is more costly). With strong typing , type errors can always be detected unless variables are explicitly cast to a different type. Weak typing occurs when languages allow implicit casting—for example, to enable operations between variables of different types without the programmer making an explicit type conversion. The more cases in which this type coercion

2070-496: Is frequently abbreviated as "GoF". That same year, the first Pattern Languages of Programming Conference was held, and the following year the Portland Pattern Repository was set up for documentation of design patterns. The scope of the term remains a matter of dispute. Notable books in the design pattern genre include: Although design patterns have been applied practically for a long time, formalization of

2160-500: Is in a way just a natural extension of Richard Montague's approach in "The Proper Treatment of Quantification in Ordinary English" (PTQ), writing that "with the benefit of hindsight, a limited form of continuation-passing is clearly discernible at the core of Montague’s (1973) PTQ treatment of NPs as generalized quantifiers". The extent to which continuations can be used to explain other general phenomena in natural language

2250-520: Is needed because in continuation-passing style no function ever returns; all calls are tail calls. One area that has seen practical use of continuations is in Web programming . The use of continuations shields the programmer from the stateless nature of the HTTP protocol. In the traditional model of web programming, the lack of state is reflected in the program's structure, leading to code constructed around

2340-403: Is often used to specify the execution semantics of languages commonly used in practice. A significant amount of academic research goes 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. A data type

2430-540: Is possible to write programs in continuation-passing style and manually implement call/cc. (In continuation-passing style, call/cc becomes a simple function that can be written with lambda .) This is a particularly common strategy in Haskell , where it is easy to construct a "continuation-passing monad " (for example, the Cont monad and ContT monad transformer in the mtl library). The support for proper tail calls

2520-487: Is primarily focused on C++) are simplified or eliminated (via direct language support) in Lisp or Dylan . Related observations were made by Hannemann and Kiczales who implemented several of the 23 design patterns using an aspect-oriented programming language (AspectJ) and showed that code-level dependencies were removed from the implementations of 17 of the 23 design patterns and that aspect-oriented programming could simplify

2610-444: Is sometimes used interchangeably with "programming language". However, usage of these terms varies among authors. In one usage, programming languages are described as a subset of computer languages. Similarly, the term "computer language" may be used in contrast to the term "programming language" to describe languages used in computing but not considered programming languages – for example, markup languages . Some authors restrict

2700-474: Is stored. The simplest user-defined type is an ordinal type whose values can be mapped onto the set of positive integers. Since the mid-1980s, most programming languages also support abstract data types , in which the representation of the data and operations are hidden from the user , who can only access an interface . The benefits of data abstraction can include increased reliability, reduced complexity, less potential for name collision , and allowing

2790-556: Is the escape continuation that may be used to escape the current context to a surrounding one. Many languages which do not explicitly support continuations support exception handling , which is equivalent to escape continuations and can be used for the same purposes. C's setjmp/longjmp are also equivalent: they can only be used to unwind the stack . Escape continuations can also be used to implement tail call elimination . One generalization of continuations are delimited continuations . Continuation operators like call/cc capture

Continuation - Misplaced Pages Continue

2880-442: Is the potential for errors to go undetected. Complete type inference has traditionally been associated with functional languages such as Haskell and ML . With dynamic typing, the type is not attached to the variable but only the value encoded in it. A single variable can be reused for a value of a different type. Although this provides more flexibility to the programmer, it is at the cost of lower reliability and less ability for

2970-402: Is used (in languages that require such declarations) or that the labels on the arms of a case statement are distinct. 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

3060-481: 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 : This grammar specifies the following: 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

3150-557: The CPU that performs instructions on data is separate, and data must be piped back and forth to the CPU. The central elements in these languages are variables, assignment , and iteration , which is more efficient than recursion on these machines. Many programming languages have been designed from scratch, altered to meet new needs, and combined with other languages. Many have eventually fallen into disuse. The birth of programming languages in

3240-418: The actor model , process calculi , and lambda calculus . These models rely on programmers or semantics engineers to write mathematical functions in the so-called continuation-passing style . This means that each function consumes a function that represents the rest of the computation relative to this function call. To return a value, the function calls this "continuation function" with a return value; to abort

3330-485: The backtracking mechanism in Prolog ; monads in functional programming ; and threads . The Scheme programming language includes the control operator call-with-current-continuation (abbreviated as: call/cc) with which a Scheme program can manipulate the flow of control: Using the above, the following code block defines a function test that sets the-continuation to the future execution state of itself: For

3420-439: The entire remaining computation at a given point in the program and provide no way of delimiting this capture. Delimited continuation operators address this by providing two separate control mechanisms: a prompt that delimits a continuation operation and a reification operator such as shift or control . Continuations captured using delimited operators thus only represent a slice of the program context. Continuations are

3510-455: The 1950s was stimulated by the desire to make a universal programming language suitable for all machines and uses, avoiding the need to write code for different computers. By the early 1960s, the idea of a universal language was rejected due to the differing requirements of the variety of purposes for which code was written. Desirable qualities of programming languages include readability, writability, and reliability. These features can reduce

3600-680: The QNP "everyone" behaves very differently from the non-quantificational noun phrase "Bob" in contributing towards the meaning of a sentence like "Alice sees [Bob/everyone]"), scope displacement (e.g., that "a raindrop fell on every car" is interpreted typically as ∀ c ∃ r , fell ( r , c ) {\displaystyle \forall c\exists r,{\mbox{fell}}(r,c)} rather than as ∃ r ∀ c , fell ( r , c ) {\displaystyle \exists r\forall c,{\mbox{fell}}(r,c)} ), and scope ambiguity (that

3690-487: The code is reached; this is called finalization. There is a tradeoff between increased ability to handle exceptions and reduced performance. For example, even though array index errors are common C does not check them for performance reasons. Although programmers can write code to catch user-defined exceptions, this can clutter a program. Standard libraries in some languages, such as C, use their return values to indicate an exception. Some languages and their compilers have

Continuation - Misplaced Pages Continue

3780-410: The computation it returns a value. Functional programmers who write their programs in continuation-passing style gain the expressive power to manipulate the flow of control in arbitrary ways. The cost is that they must maintain the invariants of control and continuations by hand, which can be a highly complex undertaking (but see 'continuation-passing style' below). Continuations simplify and clarify

3870-411: The concept in more detail. In "Continuations and the nature of quantification", Chris Barker introduced the "continuation hypothesis", that some linguistic expressions (in particular, QNPs [quantificational noun phrases]) have denotations that manipulate their own continuations. Barker argued that this hypothesis could be used to explain phenomena such as duality of NP meaning (e.g., the fact that

3960-419: The concept of design patterns languished for several years. Design patterns can speed up the development process by providing proven development paradigms. Effective software design requires considering issues that may not become apparent until later in the implementation. Freshly written code can often have hidden, subtle issues that take time to be detected; issues that sometimes can cause major problems down

4050-487: The continuation in his second Lisp implementation for the IBM 704 , though he did not name it. Reynolds (1993) gives a complete history of the discovery of continuations. First-class continuations are a language's ability to completely control the execution order of instructions. They can be used to jump to a function that produced the call to the current function, or to a function that has previously exited. One can think of

4140-402: The cost of increased storage space and more complexity. Other data types that may be supported include lists , associative (unordered) arrays accessed via keys, records in which data is mapped to names in an ordered structure, and tuples —similar to records but without names for data fields. Pointers store memory addresses, typically referencing locations on the heap where other data

4230-408: The cost of readability. 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. Alan Perlis was similarly dismissive of

4320-432: The cost of training programmers in a language, the amount of time needed to write and maintain programs in the language, the cost of compiling the code, and increase runtime performance. Programming language design often involves tradeoffs. For example, features to improve reliability typically come at the cost of performance. Increased expressivity due to a large number of operators makes writing code easier but comes at

4410-433: The details of the hardware, instead being designed to express algorithms that could be understood more easily by humans. For example, arithmetic expressions could now be written in symbolic notation and later translated into machine code that the hardware could execute. In 1957, Fortran (FORmula TRANslation) was invented. Often considered the first compiled high-level programming language, Fortran has remained in use into

4500-888: The final application classes or objects that are involved. Patterns that imply mutable state may be unsuited for functional programming languages. Some patterns can be rendered unnecessary in languages that have built-in support for solving the problem they are trying to solve, and object-oriented patterns are not necessarily suitable for non-object-oriented languages. Design patterns can be organized into groups based on what kind of problem they solve. Creational patterns create objects. Structural patterns organize classes and objects to form larger structures that provide new functionality. Behavioral patterns provide communication between objects and realizing these patterns. J2EE Patterns PoEAA Can be unsafe when implemented in some language/hardware combinations. It can therefore sometimes be considered an anti-pattern . The documentation for

4590-461: The first programming languages. The earliest computers were programmed in first-generation programming languages (1GLs), machine language (simple instructions that could be directly executed by the processor). This code was very difficult to debug and was not portable between different computer systems. In order to improve the ease of programming, assembly languages (or second-generation programming languages —2GLs) were invented, diverging from

SECTION 50

#1732773361838

4680-524: The functional expression of the GOTO statement, and the same caveats apply. While they are a sensible option in some special cases such as web programming, use of continuations can result in code that is difficult to follow. In fact, the esoteric programming language Unlambda includes call-with-current-continuation as one of its features solely because expressions involving it "tend to be hopelessly difficult to track down." The external links below illustrate

4770-448: The heap), and rather than calling a "make sandwich" routine and then returning, the person called a "make sandwich with current continuation" routine, which creates the sandwich and then continues where execution left off. Scheme was the first full production system providing first "catch" and then call/cc . Bruce Duba introduced call/cc into SML . Continuations are also used in models of computation including denotational semantics ,

4860-496: The idea of applying patterns to programming – specifically pattern languages – and presented their results at the OOPSLA conference that year. In the following years, Beck, Cunningham and others followed up on this work. Design patterns gained popularity in computer science after the book Design Patterns: Elements of Reusable Object-Oriented Software was published in 1994 by the so-called "Gang of Four" (Gamma et al.), which

4950-400: The idea. Software design pattern In software engineering , a Design Pattern describes a relatively small, well-defined aspect (i.e. functionality) of a computer program in terms of how to write the code . Using a pattern is intended to leverage an existing concept rather than re-inventing it. This can decrease the time to develop software and increase the quality of

5040-538: The implementation of several common design patterns , including coroutines / green threads and exception handling , by providing the basic, low-level primitive which unifies these seemingly unconnected patterns. Continuations can provide elegant solutions to some difficult high-level problems, like programming a web server that supports multiple pages, accessed by the use of the forward and back buttons and by following links. The Smalltalk Seaside web framework uses continuations to great effect, allowing one to program

5130-658: The implementations of design patterns. See also Paul Graham's essay "Revenge of the Nerds". Inappropriate use of patterns may unnecessarily increase complexity. FizzBuzzEnterpriseEdition offers a humorous example of over-complexity introduced by design patterns. . By definition, a pattern must be programmed anew into each application that uses it. Since some authors see this as a step backward from software reuse as provided by components , researchers have worked to turn patterns into components. Meyer and Arnout were able to provide full or partial componentization of two-thirds of

5220-402: The invention of the microprocessor , computers in the 1970s became dramatically cheaper. New computers also allowed more user interaction, which was supported by newer programming languages. Lisp , implemented in 1958, was the first functional programming language. Unlike Fortran, it supported recursion and conditional expressions , and it also introduced dynamic memory management on

5310-429: 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

5400-417: 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. The first programmable computers were invented at the end of the 1940s, and with them,

5490-511: The machine language to make programs easier to understand for humans, although they did not increase portability. Initially, hardware resources were scarce and expensive, while human resources were cheaper. Therefore, cumbersome languages that were time-consuming to use, but were closer to the hardware for higher efficiency were favored. The introduction of high-level programming languages ( third-generation programming languages —3GLs)—revolutionized programming. These languages abstracted away

SECTION 60

#1732773361838

5580-400: The meaning of languages, as opposed to their form ( syntax ). Static semantics defines restrictions on the structure of valid texts that are hard or impossible to express in standard syntactic formalisms. 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

5670-739: The motif to their codebase to solve the problem described by the pattern. The resulting code has structure and organization similar to the chosen motif. Efforts have also been made to codify design patterns in particular domains, including the use of existing design patterns as well as domain-specific design patterns. Examples include user interface design patterns, information visualization , secure design, "secure usability", Web design and business model design. The annual Pattern Languages of Programming Conference proceedings include many examples of domain-specific patterns. Object-oriented design patterns typically show relationships and interactions between classes or objects , without specifying

5760-639: The new programming languages uses static typing while a few numbers of new languages use dynamic typing like Ring and Julia . Some of the new programming languages are classified as visual programming languages like Scratch , LabVIEW and PWCT . Also, some of these languages mix between textual and visual programming usage like Ballerina . Also, this trend lead to developing projects that help in developing new VPLs like Blockly by Google . Many game engines like Unreal and Unity added support for visual scripting too. Every programming language includes fundamental elements for describing data and

5850-455: The operations or transformations applied to them, such as adding two numbers or selecting an item from a collection. These elements are governed by syntactic and semantic rules that define their structure and meaning, respectively. 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

5940-436: The option of turning on and off error handling capability, either temporarily or permanently. One of the most important influences on programming language design has been computer architecture . Imperative languages , the most commonly used type, were designed to perform well on von Neumann architecture , the most common computer architecture. In von Neumann architecture, the memory stores both data and instructions, while

6030-436: The order of execution of key instructions via the use of semaphores , controlling access to shared data via monitor , or enabling message passing between threads. Many programming languages include exception handlers, a section of code triggered by runtime errors that can deal with them in two main ways: Some programming languages support dedicating a block of code to run regardless of whether an exception occurs before

6120-483: The other hand, some programming languages are graphical , 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

6210-442: 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. 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. The term semantics refers to

6300-505: The popular von Neumann architecture . While early programming languages were closely tied to the hardware , over time they have developed more abstraction to hide implementation details for greater simplicity. Thousands of programming languages—often classified as imperative, functional , logic , or object-oriented —have been developed for a wide variety of uses. Many aspects of programming language design involve tradeoffs—for example, exception handling simplifies error handling, but at

6390-585: 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 . Some languages, including Perl and Lisp, contain constructs that allow execution during

6480-489: The programmer specifies a desired result and allows the interpreter to decide how to achieve it. During the 1980s, the invention of the personal computer transformed the roles for which programming languages were used. New languages introduced in the 1980s included C++, a superset of C that can compile C programs but also supports classes and inheritance . Ada and other new languages introduced support for concurrency . The Japanese government invested heavily into

6570-417: The programmer. Storing an integer in a type that is too small to represent it leads to integer overflow . The most common way of representing negative numbers with signed types is twos complement , although ones complement is also used. Other common types include Boolean —which is either true or false—and character —traditionally one byte , sufficient to represent all ASCII characters. Arrays are

6660-420: The programming language to check for errors. Some languages allow variables of a union type to which any type of value can be assigned, in an exception to their usual static typing rules. In computing, multiple instructions can be executed simultaneously. Many programming languages support instruction-level and subprogram-level concurrency. By the twenty-first century, additional processing power on computers

6750-432: The refrigerator and make yourself a sandwich, which is now sitting on the counter. You invoke the continuation in your pocket, and you find yourself standing in front of the refrigerator again, thinking about a sandwich. But fortunately, there's a sandwich on the counter, and all the materials used to make it are gone. So you eat it. :-) In this description, the sandwich is part of the program data (e.g., an object on

6840-520: The resulting program. Notably, a pattern does not consist of a software artifact . Most development resources that a programmer uses involve configuring the codebase to use an artifact; for example a library . In contrast, to use a pattern, a programmer writes code as described by the pattern. The result is unique every time even though the result may be recognizable as based on the pattern. Some consider using patterns to be best practice for software design . Some consider using design patterns as

6930-402: The road. Reusing design patterns can help to prevent such issues, and enhance code readability for those familiar with the patterns. Software design techniques are difficult to apply to a broader range of problems. Design patterns provide general solutions, documented in a format that does not require specifics tied to a particular problem. In 1996, Christopher Alexander was invited to give

7020-404: 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

7110-686: The so-called fifth-generation languages that added support for concurrency to logic programming constructs, but these languages were outperformed by other concurrency-supporting languages. Due to the rapid growth of the Internet and the World Wide Web in the 1990s, new programming languages were introduced to support Web pages and networking . Java , based on C++ and designed for increased portability across systems and security, enjoyed large-scale success because these features are essential for many Internet applications. Another development

7200-525: The term "programming language" to Turing complete languages. Most practical programming languages are Turing complete, and as such are equivalent in what programs they can compute. 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. John C. Reynolds emphasizes that formal specification languages are just as much programming languages as are

7290-401: The twenty-first century. Around 1960, the first mainframes —general purpose computers—were developed, although they could only be operated by professionals and the cost was extreme. The data and instructions were input by punch cards , meaning that no input could be added while the program was running. The languages developed at this time therefore are designed for minimal interaction. After

7380-424: The twenty-first century. C allows access to lower-level machine operations more than other contemporary languages. Its power and efficiency, generated in part with flexible pointer operations, comes at the cost of making it more difficult to write correct code. Prolog , designed in 1972, was the first logic programming language, communicating with a computer using formal logic notation. With logic programming,

7470-475: The underlying data structure to be changed without the client needing to alter its code. In static typing , all expressions have their types determined before a program executes, typically at compile-time. Most widely used, statically typed programming languages require the types of variables to be specified explicitly. In some languages, types are implicit; one form of this is when the compiler can infer types based on context. The downside of implicit typing

7560-596: The variables its functions use. Most programming languages use a call stack for storing the variables needed because it allows for fast and simple allocating and automatic deallocation of memory. Other programming languages use a heap for this, which allows for flexibility at a higher cost for allocating and deallocating memory. Both of these implementations have benefits and drawbacks in the context of continuations. Many programming languages exhibit first-class continuations under various names; specifically: In any language which supports closures and proper tail calls , it

7650-914: The web server in procedural style, by switching continuations when switching pages. More complex constructs for which "continuations provide an elegant description" also exist. For example, in C , longjmp can be used to jump from the middle of one function to another, provided the second function lies deeper in the stack (if it is waiting for the first function to return, possibly among others). Other more complex examples include coroutines in Simula 67 , Lua , and Perl ; tasklets in Stackless Python ; generators in Icon and Python ; continuations in Scala (starting in 2.8); fibers in Ruby (starting in 1.9.1);

7740-476: Was service-oriented programming , designed to exploit distributed systems whose components are connected by a network. Services are similar to objects in object-oriented programming, but run on a separate process. C# and F# cross-pollinated ideas between imperative and functional programming. After 2010, several new languages— Rust , Go , Swift , Zig and Carbon —competed for the performance-critical software for which C had historically been used. Most of

7830-407: Was increasingly coming from the use of additional processors, which requires programmers to design software that makes use of multiple processors simultaneously to achieve improved performance. Interpreted languages such as Python and Ruby do not support the concurrent use of multiple processors. Other programming languages do support managing data shared between different threads by controlling

7920-550: Was limited, most popular imperative languages—including C , Pascal , Ada , C++ , Java , and C# —are directly or indirectly descended from ALGOL 60. Among its innovations adopted by later programming languages included greater portability and the first use of context-free , BNF grammar. Simula , the first language to support object-oriented programming (including subtypes , dynamic dispatch , and inheritance ), also descends from ALGOL and achieved commercial success. C, another ALGOL descendant, has sustained popularity into

8010-430: Was that of dynamically typed scripting languages — Python , JavaScript , PHP , and Ruby —designed to quickly produce small programs that coordinate existing applications . Due to their integration with HTML , they have also been used for building web pages hosted on servers . During the 2000s, there was a slowdown in the development of new programming languages that achieved widespread popularity. One innovation

8100-402: Was to simplify a program and thus make its result more clear. Christopher Strachey , Christopher P. Wadsworth and John C. Reynolds brought the term continuation into prominence in their work in the field of denotational semantics that makes extensive use of continuations to allow sequential programs to be analysed in terms of functional programming semantics. Steve Russell invented

#837162