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106-532: POP-2 (also called POP2 ) is a programming language developed around 1970 from the earlier language POP-1 (developed by Robin Popplestone in 1968, originally named COWSEL ) by Robin Popplestone and Rod Burstall at the University of Edinburgh . It drew roots from many sources: the languages Lisp and ALGOL 60 , and theoretical ideas from Peter J. Landin . It used an incremental compiler , which gave it some of
212-426: 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
318-490: A doublet function : this is a function that had another function attached as its updater , which is called on the receiving side of an assignment. Thus, if the variable a contains an array, then is equivalent to the builtin function updater returning the updater of the doublet. Of course, updater is a doublet and can be used to change the updater component of a doublet. Variables can hold values of any type, including functions, which are first-class objects. Thus,
424-406: 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
530-410: A limit register ( base and bounds ), preventing one program interfering with another. The System/360 gave each process and every 2048-byte block of memory a four-bit key, and if a process key did not match the memory block key an exception would result. The 1900 system required programs to occupy a contiguous area of memory but allowed processes to be relocated during execution, simplifying the work of
636-400: 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,
742-447: 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
848-472: A different model number for floating point equipped machines. The 22-bit addressing mode and extended branch mode introduced by the 1906 was extended to the 1902A and 1903A, but not the much smaller 1901A. ICL introduced a paging unit to the higher end machines (1904A, 1906A) and a new version of the GEORGE operating system, GEORGE 4, which was compatible with GEORGE 3 but used paged virtual memory in place of
954-464: A family of compatible machines spanning nearly the complete range of customer needs. It was immediately obvious that ICT would need a coherent response. Two paths were available: develop a range of machines based on the FP6000, using the flexibility of its design to produce smaller or larger machines, or cooperate with RCA who were re-targeting their development to a System/360 compatible range to be known as
1060-422: 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,
1166-454: 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
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#17330937067301272-423: A theoretical 4Mword maximum memory. Instructions contained a 12-bit operand, either fixed or offset from an index register. Branch instructions held a 15-bit offset, allowing access to all memory on the initial range. When the address size was increased to 22 bits, replaced ( indirect ) and relative branches were added to the instruction set to allow access to the larger address space. The largest change between
1378-523: A user program did not need to know which physical disk was being used for a file. In December 1964, ICT set up an Operating Systems Branch to develop a new operating system for the 1906/7. The branch was initially staffed with people being released by the end of work on the OMP operating system for the Ferranti Orion . The initial design of the new system, named George in part after George E. Felton , head of
1484-495: A variety of data structures . In parallel with that, Steve Hardy at University of Sussex implemented a subset of POP-2, which he named POP-11 which ran on a Digital Equipment Corporation (DEC) PDP-11/40 computer. It was originally designed to run on the DEC operating system RSX-11D, in time-shared mode for teaching, but that caused so many problems that an early version of Unix was installed and used instead. That version of Pop-11
1590-406: 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
1696-421: 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
1802-415: 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
1908-402: Is already on the stack (in this case 3), after which the original function poly2 is invoked. It then uses the top four items on the stack, producing the same result as i.e. In POP-2, it was possible to define new operations (operators in modern terms). The first line declares a new operation +* with precedence (priority) 3. The second line creates a function f(x,y)=x*x+y*y, and assigns it to
2014-419: 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
2120-469: 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
2226-403: 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
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#17330937067302332-444: 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
2438-474: 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
2544-409: Is that the language has explicit notion of an operand stack . Thus, the prior assignment can be written as two separate statements : which evaluates the value 3 and leaves it on the stack, and which pops the top value off the stack and assigns it to the variable 'a'. Similarly, the function call can be written as (commas and semicolons being largely interchangeable) or even or Because of
2650-442: 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
2756-402: 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
2862-481: 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
2968-551: 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
3074-569: The RCA Spectra 70 . One major consideration was that the FP6000 was already running, while the RCA Spectra range would take some years to become available. In the end, the decision was made to go with a range of machines based on the FP6000. The centrepiece of the new range was the ICT 1904, a version of the FP6000 with the ICT standard peripheral interface. For higher-end machines, a new larger processor,
3180-410: 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
3286-622: The stack-based paradigm, there is no need to distinguish between statements and expressions ; thus, the two constructs and are equivalent (use of close , as endif hadn't become a common end-of-if-clause notation yet). There are no special language constructs to create arrays or record structures as they are commonly understood: instead, these are created with the aid of special builtin functions, e.g., newarray (for arrays that can contain any type of item) and newanyarray to create restricted types of items. Thus, array element and record field accessors are simply special cases of
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3392-469: The 1900 needed at least two words. The eight-bit byte of the System/360 allowed manipulation of lowercase characters without the complex shift sequences of the 1900. However, in the early days the smaller word size of the 1900 was seen as a cost advantage, as the memory could be 25% cheaper for the same number of words. The initial range of machines was: The execution time for an addition instruction ("add
3498-542: The 1906A, the 1908A (known internally as Project 51), which would allow ICL to compete with the large CDC and IBM machines in universities and research centers but it was eventually abandoned in favor of accelerating work on the New Range , which was being designed to replace both the 1900 series and the ICL System 4 . With the A series a hardware floating point unit was made an optional feature of all machines, instead of having
3604-455: 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
3710-580: The AI2 (Artificial Intelligence, 2nd year level) class using the EMAS operating system. This implementation was written from scratch in the Edinburgh programming language, IMP . Later versions were implemented for Computer Technology Limited (CTL) Modular One, PDP-10 , ICL 1900 series (running the operating system George ). Julian Davies, in Edinburgh, implemented an extended version of POP-2, which he named POP-10 on
3816-570: The Basic Programming Division, was based on ideas from the Orion and the spooling system of the Atlas computer. The initial version, George 1 (for the ICT 1901, 1902 and 1903 machines), was a simple batch processing system. Job descriptions were read in from cards or paper tape , peripherals and magnetic tape files were dynamically allocated to the job, which was then run, producing output on
3922-574: The Business Equipment Exhibition, Olympia . The first commercial sale was made in 1964 to the Morgan Crucible Company , comprising a 16K word 1902 with an 80-column 980-card/minute reader, a card punch, a 600 line/min printer and 4 x 20kchar/s tape drives . It was soon upgraded to a 32K word memory and a floating point unit to allow for some scientific work. The same company had also been the first to order ICT's first computer,
4028-421: The E series machines: Improvements to the memory subsystems of these machines, replacing the 1.8μs core with 0.75μs core, were introduced as the F series. (ICT merged with English Electric Computers to form ICL on 9 July 1968. Thus although the E series had been designed by ICT many, if not all, were delivered with ICL badges). In 1969 the 1900 A series was delivered, replacing the remaining machines from
4134-566: The FP6000 as their medium-sized processor in the 1965–1968 timeframe, replacing the ICT 1302 . Another plan being considered was to license a new range of machines being developed by RCA , probably compatible with the expected IBM 8000 . The initial 1900 range did not suffer from the many years of careful planning behind the IBM 360. -- Virgilio Pasquali On 7 April 1964 IBM announced the System/360 series,
4240-410: The FP6000 executive was provided with the ICT 1904/1905, and new versions were written for the ICT 1906/7 and ICT 1901/2/3. An important task of these different versions was to hide the hardware differences between the different machines, providing emulation of missing instructions as extracodes . The concept was that applications, and later operating systems, were written to run on the combination of
4346-711: The HEC4 (later ICT 1201), in 1955. The first system delivered was a 1904, for the Northampton College of Advanced Technology , London, in January 1965. The ICT 1900 was a word-addressing machine using a register -to-memory architecture with eight accumulator registers, three of which could be used as modifier ( index ) registers. The word length was 24 bits , which could be used as four six-bit characters; instructions were provided for copying single characters to and from memory. The accumulators were addressable as if they were
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4452-534: The I/O operations on behalf of user programs, allowing allocation of different peripherals as needed. Despite its simplicity executive was, for the time, quite powerful, allocating memory to programs as needed (rather than the fixed partitions provided by OS/360 ). This was possible because the FP6000 design contained hardware to aid multi-programming , datum and limit registers, which made programs address independent (relocatable) and prevented one program from accessing
4558-599: The ICL 1901 and 1902 models. To recapture the market, an ICL project known internally as PF73 was started, based on an ICL Stevenage-developed microprogrammed machine known as MICOS-1, which came to market in 1973 as the ICL 2903 and 2904. Despite their New Range numbering, these machines used the ICL 1900 instruction set and ran 1900 software, although a microprogram was available that provided an IBM-360 instruction set to allow them to run IBM software. The 2903/2904 were released with an RPG compiler to better compete with System/3 . It
4664-619: The ICT 1906, was to be developed by the ICT West Gorton unit (formerly part of Ferranti). To meet the needs of smaller customers, smaller machines, the ICT 1901 and ICT 1902/3, were developed by the ICT Stevenage unit, based on the PF182 and PF183 processors already in development. On 29 September 1964 the ICT 1900 range was announced in a filmed presentation, scripted by Antony Jay . The following week two working systems were demonstrated at
4770-563: The Odra machines ran standard ICL software (executive E6RM, George 3). Second generation "S3E" (microcoded) versions of the larger New Range systems (such as the 2960/2966 from West Gorton, and the later 2940/50 from Stevenage), could run 1900 series code under DME ( Direct Machine Environment ) as an emulation as well as the New Range instruction set under the newer VME (Virtual Machine Environment). Later CME (Concurrent Machine Environment) microcode
4876-619: The PDP-10 computer running TOPS-10 . This was the first dialect of POP-2 that treated case as significant in identifier names, used lower case for most system identifiers, and supported long identifiers with more than 8 characters. Shortly after that, a new implementation known as WPOP (for WonderPop) was implemented by Robert Rae and Allan Ramsay in Edinburgh, on a research-council funded project. That version introduced caged address spaces, some compile-time syntactic typing (e.g., for integers and reals), and some pattern matching constructs for use with
4982-487: 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
5088-420: The compiler and all its subroutines at run time made it possible to support far richer language extensions than are possible with Macros, and as a result Pop-11 was used (by Steve Hardy, Chris Mellish and John Gibson) to produce an implementation of Prolog , using the standard syntax of Prolog, and the combined system became known as Poplog , to which Common Lisp and Standard ML were added later. This version
5194-717: The contents of store location x to register y") ranged from 2.5 μs for a 1906 or 1907 with 1.1 μs core store, to 34 μs for a 1901 with 6 μs core store. All machines except the 1901 were operated from a modified Teletype Model 33 ASR used to give commands to the executive . The 1901 was operated from console switches, with a console available as an optional extra. A range of peripherals was available, including 80-column card punches and readers, 8 track paper tape punches and readers and solid barrel line printers . Data could be stored on open-reel half-inch magnetic tape or one-inch 8-track magnetic tape cassettes. Magnetic disk storage became available in 1966. In 1968 ICT introduced
5300-402: 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
5406-408: 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
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#17330937067305512-432: 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
5618-433: 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
5724-503: The executive using extracodes , instructions that caused a trap into the executive. The executive would then communicate with the appropriate peripheral via the Standard Interface, using functions not available to user processes. The subsequent data transfers would then occur across this interface, autonomously without further program involvement. The conclusion of the transfers (or error if any) would similarly be indicated back to
5830-432: The executive. On smaller members of the series, some expensive instructions ( floating point for example) were also implemented as extracodes. The combination of the executive and hardware provided the same interface to programs running on any model of the range. The hardware floating-point unit, if fitted, ran autonomously. After a floating-point operation was started, integer instructions could be run in parallel until
5936-429: The first eight words of memory, giving the effect of register-to-register instructions with no extra operation codes being needed. The hardware registers were an optional feature, and if not fitted the accumulators were the first eight words of memory. The large number of optional features in the FP6000 design gave ICT great flexibility in pricing. A notable feature of the series was the hardware support (in all except
6042-461: 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
6148-405: The flexibility of an interpreted language , including allowing new function definitions at run time and modification of function definitions while a program runs (both of which are features of dynamic compilation ), without the overhead of an interpreted language. POP-2's syntax is ALGOL -like, except that assignments are in reverse order: instead of writing one writes The reason for this
6254-406: The following constructs and are equivalent. An interesting operation on functions is partial application , (sometimes termed currying ). In partial application, some number of the rightmost arguments of the function (which are the last ones placed on the stack before the function is involved) are frozen to given values, to produce a new function of fewer arguments, which is a closure of
6360-490: The full 128 characters of ASCII . Character #74 (i.e. octal 74) was considered an alpha shift and indicated subsequent characters were to be considered uppercase, #75 was a beta shift and indicated subsequent characters were in lower case, and #76 the delta shift, indicating the next character was a control character. Thus the ASCII string "Hello World" would be encoded as " αHβELLO αWβORLD ". Character #77
6466-477: The hardware and the executive, and so would run on any member of the series, no matter how different the underlying hardware was. With the introduction of magnetic disk systems executive became more complex, using overlaying to reduce its memory footprint . Disk based executives included features to simplify disk operations, handling file management (creation, renaming, deletion, resizing) on behalf of user programs. Files were identified by 12-character names, and
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#17330937067306572-540: The idea. ICT 1900 series ICT 1900 was a family of mainframe computers released by International Computers and Tabulators (ICT) and later International Computers Limited (ICL) during the 1960s and 1970s. The 1900 series was notable for being one of the few non-American competitors to the IBM System/360 , enjoying significant success in the European and British Commonwealth markets. In early 1963, ICT
6678-465: The initial series and the E/F machines. The original discrete germanium semiconductor implementations were replaced by Texas Instruments 7400 series TTL integrated circuits in most of the range and Motorola MECL 10K ECL integrated circuits in the new 1906A (which was based on the original 1906 rather than the dual processor 1904 of the 1906E/F). There was a proposal to build a multiprocessor version of
6784-402: 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
6890-429: 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
6996-417: 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,
7102-511: 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
7208-400: 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
7314-429: The memory allocated to another. To allow more efficient use of peripherals, as well running multiple programs simultaneously, executive allowed a limited multi-threading within programs (each program could be split into up to four sub-programs, sharing the same address space, which were also time-shared; while one sub-program was waiting for peripheral activity another could continue processing). An extended version of
7420-639: 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
7526-528: The newly declared operation +*. The original version of POP-2 was implemented on an Elliott 4130 computer in the University of Edinburgh (with only 64 KB RAM, doubled to 128 KB in 1972). POP-2 was ported to the ICT 1900 series on a 1909 at Lancaster University by John Scott in 1968. In the mid-1970s, POP-2 was ported to BESM-6 (POPLAN System). In 1978 Hamish Dewar implemented a version of POP-2 specifically for use by Edinburgh University undergraduates in
7632-455: The operating system. The 1900 also allowed any process direct access to the first 4096 words of its address space. (Both the 1900 and 360 had a 12-bit operand field, but on the 360 addresses were physical addresses so a program could directly access the first 4096 bytes of physical memory). The System/360 had the advantage of a larger word and character size; its 32-bit words were large enough for (low accuracy) floating point numbers whereas
7738-455: 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
7844-436: 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
7950-436: 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
8056-421: The original FP6000 and the 1900 series was the inclusion of the ICT standard interface for connection of peripherals. This allowed connection of any ICT peripheral to any processor of the series, and owners could upgrade their processors while keeping the same peripherals or vice versa. All I/O operations were initiated by a privileged supervisor process, known as the executive . User processes communicated with
8162-416: The original function. For instance, consider a function for computing general second-degree polynomials: This can be bound, for instance as such that the expression applies the closure of poly2 with three arguments frozen, to the argument 3, returning the square of (3 - 1), which is 4. The application of the partially applied function causes the frozen values (in this case 1, -2, 1) to be added to whatever
8268-483: 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
8374-442: 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
8480-580: 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
8586-489: 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
8692-417: 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
8798-420: 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
8904-478: The range new models were released. In each case the model was simply based on the next higher model of the previous range, the 1903T being based on the 1904S for example. During and after the production of the 1900 series a number of compatible (or clone ) machines were produced by ICL licensees, as well as competitors. In 1969 IBM had introduced the System/3 entry-level machine, which began to cut into sales of
9010-400: The result of the floating-point operation was needed. The instruction set supported the following data formats: Since the ICT 1900 used a six-bit character it was largely limited to a 64-character repertoire, with only upper case letters and no control characters . In order to deal with data on paper tape or from communications equipment, a system of shifts could be used to represent
9116-404: 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
9222-448: The simple datum/limit system of the earlier machines. In April 1971 ICL announced the S series of machines, replacing the core store of the earlier machines with semiconductor memory in most of the range and very fast Plessey nickel plated wire memory for the top of the range 1906S. As the larger models of the new range were being introduced it was decided that the lower models of the 1900 range were becoming uncompetitive. To refresh
9328-461: The smallest processors) for running multiple processes – every process ran in an independent address space, enforced by datum and limit registers. No user process could access the memory of any other process. Later models added paging hardware, allowing true virtual memory with the GEORGE 4 operating system. On the original models the address size was 15 bits, allowing up to 32K words of memory. Later models added 22-bit addressing, allowing
9434-674: 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
9540-525: 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
9646-401: 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
9752-424: 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,
9858-475: 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
9964-476: The use of close for all loops in POP-2. Pop-11 also introduced a pattern matcher for list structures, making it far easier to teach artificial intelligence (AI) programming. Around 1980, Pop-11 was ported to a VAX-11/780 computer by Steve Hardy and John Gibson, and soon after that it was replaced by a full incremental compiler (producing machine-code instead of an interpreted intermediate code). The existence of
10070-476: 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
10176-461: Was a fill (ignore) character, similar to the rubout character in the 7-bit world. The 1900 used a variant of ASCII-63 , known by ICT as the ECMA character set, with differences in five character codes: Both the 1900 series and IBM System/360 provided hardware support for multi-programming. On the 1900, all user memory addresses were modified by a datum (base address) register and checked against
10282-501: Was a commercial success and almost 3000 machines were sold. Based on a fully microprogrammed CPU, the Stanford EMMY commercialised by Palyn Associates , the ME29 was sold as a replacement for the 2903 and 2904, still executing the 1900 order code. An EMMY processor emulating the IBM 360 order code was estimated to be around the speed of an IBM System/360 Model 50 , implying that the ME29
10388-487: Was developed, which allowed DME and VME to co-exist (and run) concurrently on the same platform, similar to the functionality offered by virtualisation software such as VMware today. The FP6000 ran under the control of operators executive , a simple operating system that allowed the operator using the system console to load programs from magnetic tape, cards or paper tape, allocate peripherals to programs and attribute priorities to running programs. Executive performed all
10494-608: Was engaged in negotiations to buy the computer business of Ferranti . In order to sweeten the deal, Ferranti demonstrated to ICT the Ferranti-Packard 6000 (FP6000) machine, which had been developed by its Canadian subsidiary Ferranti-Packard , to a design known as Harriac that had been initiated in Ferranti by Harry Johnson and fleshed out by Stanley Gill and John Iliffe. The FP6000 was an advanced design, notably including hardware support for multiprogramming . ICT considered using
10600-567: Was faster than the original ICT 1904, approaching the speed of the ICT 1906. In an effort to increase sales to ICL customers, and to profit from the difficulties ICL were having moving customers from the 1900 to the New Range, IBM introduced a microcode package for the 370/145 allowing execution of 1900 series programs. The Odra 1300 series (Odra 1304, Odra 1305 and Odra 1325) were a range of 1900 compatible machines built by Elwro in Wrocław , Poland between 1971 and 1978. By agreement with ICL
10706-467: Was implemented in an early dialect of C, using an idiosyncratic compiler made it very hard to maintain and upgrade to new versions of the Mac operating system. Also, AlphaPop was not " 32-bit clean" due to the use of high address bits as tag bits to signify the type of objects, which was incompatible with the use of memory above 8 Mb on later Macintoshes. Programming language A programming language
10812-407: 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
10918-532: Was later ported to a variety of machines and operating systems and as a result Pop-11 became the dominant dialect of POP-2, still available in the Poplog system. Around 1986, a new AI company Cognitive Applications Ltd., collaborated with members of Sussex university to produce a variant of Pop-11 named AlphaPop running on Apple Mac computers, with integrated graphics. This was used for many commercial projects, and to teach AI programming in several universities. That it
11024-550: 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
11130-430: 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
11236-548: Was written in Unix assembly language , and code was incrementally compiled to an intermediate bytecode which was interpreted. That port was completed around 1976, and as a result, Pop-11 was used in several places for teaching. To support its teaching function, many of the syntactic features of POP-2 were modified, e.g., replacing function ... end with define ... enddefine and adding a wider variety of looping constructs with closing brackets to match their opening brackets instead of
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