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70-526: Allegro Common Lisp is a programming language with an integrated development environment (IDE), developed by Franz Inc. It is a dialect of the language Lisp , a commercial software implementation of the language Common Lisp . Allegro CL provides the full American National Standards Institute (ANSI) Common Lisp standard with many extensions, including threads, CLOS streams, CLOS MOP, Unicode, SSL streams, implementations of various Internet protocols, OpenGL interface. The first version of Allegro Common Lisp
140-426: 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 the popular von Neumann architecture . While early programming languages were closely tied to
210-406: 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
280-400: 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,
350-442: A CPU interrupt could be turned into an OS signal. Some exceptions, especially hardware ones, may be handled so gracefully that execution can resume where it was interrupted. The definition of an exception is based on the observation that each procedure has a precondition , a set of circumstances for which it will terminate "normally". An exception handling mechanism allows the procedure to raise an exception if this precondition
420-447: 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
490-422: 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,
560-454: 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
630-402: A special "ZERO DIVIDE" value (circumventing the need for exceptions). Common exceptions include an invalid argument (e.g. value is outside of the domain of a function ), an unavailable resource (like a missing file, a network drive error, or out-of-memory errors ), or that the routine has detected a normal condition that requires special handling, e.g., attention, end of file. Social pressure
700-502: Is a major influence on the scope of exceptions and use of exception-handling mechanisms, i.e. "examples of use, typically found in core libraries, and code examples in technical books, magazine articles, and online discussion forums, and in an organization’s code standards". Exception handling solves the semipredicate problem , in that the mechanism distinguishes normal return values from erroneous ones. In languages without built-in exception handling such as C, routines would need to signal
770-406: 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
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#1733086075335840-421: 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 a programming language is required in order to execute programs, namely an interpreter or
910-563: Is abnormal or unusual, when in fact raising the exception may be a normal and usual situation in the program. For example, suppose a lookup function for an associative array throws an exception if the key has no value associated. Depending on context, this "key absent" exception may occur much more often than a successful lookup. The first hardware exception handling was found in the UNIVAC I from 1951. Arithmetic overflow executed two instructions at address 0 which could transfer control or fix up
980-415: 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
1050-419: 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
1120-496: Is available as freeware , a Free Express Edition (with some limits like a constrained heap space) for non-commercial use. Customers can get access to much of the source code of Allegro CL. Allegro CL includes an implementation of Prolog and an object caching database called AllegroCache. The most recent release, Allegro CL 10.1, supports Symmetric Multiprocessing. Allegro CL has been used to implement various applications: Programming language A programming language
1190-534: Is based on Unicode . It supports various external text encodings and provides string and character types based on Universal Coded Character Set 2 (UCS-2). Allegro CL can be used with and without its integrated development environment (IDE), which is available for Windows, Linux, and on macOS in version 8.2. The IDE (written in Allegro CL) includes development tools including an editor and an interface designer. Allegro CL can be used to deliver applications. Allegro CL
1260-419: Is done depend on whether it is a hardware or software exception and how the software exception is implemented. Exceptions are defined by different layers of a computer system, and the typical layers are CPU-defined interrupts , operating system (OS)-defined signals , programming language -defined exceptions. Each layer requires different ways of exception handling although they may be interrelated, e.g.
1330-469: 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
1400-403: 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
1470-444: 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
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#17330860753351540-474: 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
1610-442: 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
1680-402: 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
1750-481: 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
1820-431: Is violated, for example if the procedure has been called on an abnormal set of arguments. The exception handling mechanism then handles the exception. The precondition, and the definition of exception, is subjective . The set of "normal" circumstances is defined entirely by the programmer, e.g. the programmer may deem division by zero to be undefined, hence an exception, or devise some behavior such as returning zero or
1890-551: 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
1960-410: 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
2030-505: The interrupt handler in the interrupt vector table for that exception or interrupt condition, saves state, and switches control. Exception handling in the IEEE 754 floating-point standard refers in general to exceptional conditions and defines an exception as "an event that occurs when an operation on some particular operands has no outcome suitable for every reasonable application. That operation might signal one or more exceptions by invoking
2100-552: The user interface (UI) component hierarchy, in a way that is analogous to how errors propagate up the call stack in executing code. Here the error boundary mechanism serves as an analogue to the typical try-catch mechanism. Thus a component can ensure that errors from its child components are caught and handled, and not propagated up to parent components. For example, in Vue, a component would catch errors by implementing errorCaptured When used like this in markup: The error produced by
2170-455: 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
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2240-448: The 1996 Cluster spacecraft launch ended in a catastrophic explosion due in part to the Ada exception handling policy of aborting computation on arithmetic error. William Kahan claims the default IEEE 754 exception handling behavior would have prevented this. Front-end web development frameworks, such as React and Vue , have introduced error handling mechanisms where errors propagate up
2310-487: 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
2380-402: 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
2450-408: 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
2520-432: 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
2590-463: The default or, if explicitly requested, a language-defined alternate handling." By default, an IEEE 754 exception is resumable and is handled by substituting a predefined value for different exceptions, e.g. infinity for a divide by zero exception, and providing status flags for later checking of whether the exception occurred (see C99 programming language for a typical example of handling of IEEE 754 exceptions). An exception-handling style enabled by
2660-433: 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
2730-581: The error in some other way, such as the common return code and errno pattern. Taking a broad view, errors can be considered to be a proper subset of exceptions, and explicit error mechanisms such as errno can be considered (verbose) forms of exception handling. The term "exception" is preferred to "error" because it does not imply that anything is wrong - a condition viewed as an error by one procedure or programmer may not be viewed that way by another. The term "exception" may be misleading because its connotation of "anomaly" indicates that raising an exception
2800-461: 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
2870-412: The idea. Exception handling In computing and computer programming , exception handling is the process of responding to the occurrence of exceptions – anomalous or exceptional conditions requiring special processing – during the execution of a program . In general, an exception breaks the normal flow of execution and executes a pre-registered exception handler ; the details of how this
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2940-402: 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
3010-429: 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
3080-417: 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,
3150-511: 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
3220-400: 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
3290-639: 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
3360-455: 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
3430-436: 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
3500-436: 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
3570-483: 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
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#17330860753353640-442: 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
3710-580: 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
3780-489: 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
3850-417: 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
3920-420: 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
3990-422: The result. Software exception handling developed in the 1960s and 1970s. Exception handling was subsequently widely adopted by many programming languages from the 1980s onward. There is no clear consensus as to the exact meaning of an exception with respect to hardware. From the implementation point of view, it is handled identically to an interrupt : the processor halts execution of the current program, looks up
4060-404: 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
4130-674: 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
4200-429: The standard. The standard recommends several usage scenarios for this, including the implementation of non-default pre-substitution of a value followed by resumption, to concisely handle removable singularities . The default IEEE 754 exception handling behaviour of resumption following pre-substitution of a default value avoids the risks inherent in changing flow of program control on numerical exceptions. For example,
4270-525: 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
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#17330860753354340-401: 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
4410-424: 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,
4480-475: 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
4550-412: The use of status flags involves: first computing an expression using a fast, direct implementation; checking whether it failed by testing status flags; and then, if necessary, calling a slower, more numerically robust, implementation. The IEEE 754 standard uses the term "trapping" to refer to the calling of a user-supplied exception-handling routine on exceptional conditions, and is an optional feature of
4620-476: 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
4690-408: Was finished at the end of 1986, originally called Extended Common Lisp . Allegro CL is available for many operating systems including Microsoft Windows (32/64-bit), and many Unix and Unix-like , 32-bit or 64-bit , including macOS (Intel, 32/64-bit), Linux (32/64-bit), FreeBSD (32-bit), Solaris (x64, SPARC; 32/64-bit), UNICOS , and UTS . Internationalization and localization support
4760-407: 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
4830-550: 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
4900-430: 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
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