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66-554: The Scheme language is standardized in the official Institute of Electrical and Electronics Engineers (IEEE) standard and a de facto standard called the Revised Report on the Algorithmic Language Scheme (R n RS). A widely implemented standard is R5RS (1998). The most recently ratified standard of Scheme is "R7RS-small" (2013). The more expansive and modular R6RS was ratified in 2007. Both trace their descent from R5RS;

132-565: A certain knowledge area, which provide specialized publications, conferences, business networking and other services. In September 2008, the IEEE History Committee founded the IEEE Global History Network , which now redirects to Engineering and Technology History Wiki . The IEEE Foundation is a charitable foundation established in 1973 to support and promote technology education, innovation, and excellence. It

198-525: A function and a variable to have the same name, and requiring special notation for referring to a function as a value. This is sometimes known as the " Lisp-1 vs. Lisp-2 " distinction, referring to the unified namespace of Scheme and the separate namespaces of Common Lisp. In Scheme, the same primitives that are used to manipulate and bind data can be used to bind procedures. There is no equivalent of Common Lisp's defun and #' primitives. This subsection documents design decisions that have been taken over

264-597: A function during runtime". We can also remove clauses from the database with abolish/1 , or retract/1 . * The number after the clause's name is the number of arguments it can take. It is also called arity . We can also query the database to get the body of a clause: call is analogous to Lisp's eval function. The concept of treating code as data and the manipulation and evaluation thereof can be demonstrated very neatly in Rebol . (Rebol, unlike Lisp, does not require parentheses to separate expressions). The following

330-427: A powerful and expressive programming language." Like most modern programming languages and unlike earlier Lisps such as Maclisp , Scheme is lexically scoped: all possible variable bindings in a program unit can be analyzed by reading the text of the program unit without consideration of the contexts in which it may be called. This contrasts with dynamic scoping which was characteristic of early Lisp dialects, because of

396-450: A standard module system, allowing a split between the core language and libraries . Several drafts of the R6RS specification were released, the final version being R5.97RS. A successful vote resulted in ratifying the new standard, announced on August 28, 2007. Currently the newest releases of various Scheme implementations support the R6RS standard. There is a portable reference implementation of

462-416: A starting point of powerful mathematical logic. Second, it can reduce the requirement of programmers to consider the implementation details, because it can be used to imitate machine evaluation. Finally, the lambda calculation created a substantial meta-theory. The introduction of lexical scope resolved the problem by making an equivalence between some forms of lambda notation and their practical expression in

528-441: A symbol called var is bound to the number 10: Blocks can be nested to create arbitrarily complex block structures according to the need of the programmer. The use of block structuring to create local bindings alleviates the risk of namespace collision that can otherwise occur. One variant of let , let* , permits bindings to refer to variables defined earlier in the same construct, thus: The other variant, letrec ,

594-565: A traditional programmer's puzzle, shows that Scheme can handle continuations as first-class objects, binding them to variables and passing them as arguments to procedures. When executed this code displays a counting sequence: @*@**@***@****@*****@******@*******@********... In contrast to Common Lisp, all data and procedures in Scheme share a common namespace, whereas in Common Lisp functions and data have separate namespaces making it possible for

660-473: A working programming language. Sussman and Steele showed that the new language could be used to elegantly derive all the imperative and declarative semantics of other programming languages including ALGOL and Fortran , and the dynamic scope of other Lisps, by using lambda expressions not as simple procedure instantiations but as "control structures and environment modifiers". They introduced continuation-passing style along with their first description of Scheme in

726-509: Is also now specified in Unicode. Many standard procedures have been moved to the new standard libraries, which themselves form a large expansion of the standard, containing procedures and syntactic forms that were formerly not part of the standard. A new module system has been introduced, and systems for exception handling are now standardized. Syntax-rules has been replaced with a more expressive syntactic abstraction facility (syntax-case) which allows

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792-649: Is an American 501(c)(3) professional association for electrical engineering , electronics engineering , and other related disciplines. The IEEE has a corporate office in New York City and an operations center in Piscataway, New Jersey . The IEEE was formed in 1963 as an amalgamation of the American Institute of Electrical Engineers and the Institute of Radio Engineers . The IEEE traces its founding to 1884 and

858-448: Is an example of code in Rebol (Note that >> represents the interpreter prompt; spaces between some elements have been added for readability): ( repeat is in fact a built-in function in Rebol and is not a language construct or keyword). By enclosing the code in square brackets, the interpreter does not evaluate it, but merely treats it as a block containing words: This block has

924-420: Is annotated with footnote 4, which gives credit for the origin of the term: Following suggestion of McCullough W. S., based upon terminology due to Peirce, C. S. The researchers implicated in this quote might be neurophysiologist and cybernetician Warren Sturgis McCulloch (note the difference in the surname from the note) and philosopher, logician and mathematician Charles Sanders Peirce . Pierce indeed used

990-480: Is attributable to the use of lambda calculus to derive much of the syntax of the language from more primitive forms. For instance of the 23 s-expression-based syntactic constructs defined in the R5RS Scheme standard, 14 are classed as derived or library forms, which can be written as macros involving more fundamental forms, principally lambda. As R5RS (§3.1) says: "The most fundamental of the variable binding constructs

1056-423: Is designed to enable mutually recursive procedures to be bound to one another. (See Hofstadter's male and female sequences for the definitions used in this example.) All procedures bound in a single letrec may refer to one another by name, as well as to values of variables defined earlier in the same letrec , but they may not refer to values defined later in the same letrec . A variant of let ,

1122-445: Is desirable that the internal character code representation be identical to, or very similar to, the external code representation. In the present TRAC implementation, the internal character representation is based upon ASCII . Because TRAC procedures and text have the same representation inside and outside the processor, the term homoiconic is applicable, from homo meaning the same, and icon meaning representation. The last sentence above

1188-677: Is incorporated separately from the IEEE, although it has a close relationship to it. Members of the Board of Directors of the foundation are required to be active members of IEEE, and one third of them must be current or former members of the IEEE Board of Directors. Initially, the role of the IEEE Foundation was to accept and administer donations for the IEEE Awards program, but donations increased beyond what

1254-642: Is primarily a functional programming language. It shares many characteristics with other members of the Lisp programming language family. Scheme's very simple syntax is based on s-expressions , parenthesized lists in which a prefix operator is followed by its arguments. Scheme programs thus consist of sequences of nested lists. Lists are also the main data structure in Scheme, leading to a close equivalence between source code and data formats ( homoiconicity ). Scheme programs can easily create and evaluate pieces of Scheme code dynamically. The reliance on lists as data structures

1320-408: Is shared by all Lisp dialects. Scheme inherits a rich set of list-processing primitives such as cons , car and cdr from its Lisp progenitors. Scheme uses strictly but dynamically typed variables and supports first class procedures . Thus, procedures can be assigned as values to variables or passed as arguments to procedures. This section concentrates mainly on innovative features of

1386-424: Is that extending the language with new concepts typically becomes simpler, as data representing code can be passed between the meta and base layer of the program. The abstract syntax tree of a function may be composed and manipulated as a data structure in the meta layer, and then evaluated . It can be much easier to understand how to manipulate the code since it can be more easily understood as simple data (since

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1452-501: Is the lambda expression, because all other variable binding constructs can be explained in terms of lambda expressions." Example: a macro to implement let as an expression using lambda to perform the variable bindings. Thus using let as defined above a Scheme implementation would rewrite " (let ((a 1)(b 2)) (+ b a)) " as " ((lambda (a b) (+ b a)) 1 2) ", which reduces implementation's task to that of coding procedure instantiations. In 1998, Sussman and Steele remarked that

1518-516: The 2022 Russian invasion of Ukraine and requesting the IEEE Spectrum to acknowledge "that they have unwittingly published a piece furthering misinformation and Russian propaganda." A few days later a note from the editors was added on April 6 with an apology "for not providing adequate context at the time of publication", though the editors did not revise the original article. Homoiconicity In computer programming , homoiconicity (from

1584-587: The American Institute of Electrical Engineers . In 1912, the rival Institute of Radio Engineers was formed. Although the AIEE was initially larger, the IRE attracted more students and was larger by the mid-1950s. The AIEE and IRE merged in 1963. The IEEE is headquartered in New York City , but most business is done at the IEEE Operations Center in Piscataway, New Jersey , opened in 1975. The Australian Section of

1650-487: The Greek words homo- meaning "the same" and icon meaning "representation") is an informal property of some programming languages . A language is homoiconic if a program written in it can be manipulated as data using the language. The program's internal representation can thus be inferred just by reading the program itself. This property is often summarized by saying that the language treats code as data . The informality of

1716-419: The named let form provide support for iteration using tail recursion. Continuations in Scheme are first-class objects . Scheme provides the procedure call-with-current-continuation (also known as call/cc ) to capture the current continuation by packing it up as an escape procedure bound to a formal argument in a procedure provided by the programmer. (R5RS sec. 6.4) First-class continuations enable

1782-405: The "named let" form, has an identifier after the let keyword. This binds the let variables to the argument of a procedure whose name is the given identifier and whose body is the body of the let form. The body may be repeated as desired by calling the procedure. The named let is widely used to implement iteration. Example: a simple counter Like any procedure in Scheme, the procedure created in

1848-595: The "severe legal implications" of U.S. government sanctions against Huawei. As members of its standard-setting body, Huawei employees could continue to exercise their voting rights, attend standards development meetings, submit proposals and comment in public discussions on new standards. The ban sparked outrage among Chinese scientists on social media. Some professors in China decided to cancel their memberships. On June 3, 2019, IEEE lifted restrictions on Huawei's editorial and peer review activities after receiving clearance from

1914-600: The IEEE existed between 1972 and 1985, after which it split into state- and territory-based sections. As of 2023 , IEEE has over 460,000 members in 190 countries, with more than 66 percent from outside the United States. IEEE claims to produce over 30% of the world's literature in the electrical, electronics, and computer engineering fields, publishing approximately 200 peer-reviewed journals and magazines. IEEE publishes more than 1,700 conference proceedings every year. The published content in these journals as well as

1980-719: The R5RS standard but the second does not conform to R6RS because it does not implement the full numerical tower. Scheme supports delayed evaluation through the delay form and the procedure force . The lexical context of the original definition of the promise is preserved, and its value is also preserved after the first use of force . The promise is only ever evaluated once. These primitives, which produce or handle values known as promises , can be used to implement advanced lazy evaluation constructs such as streams . Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers ( IEEE )

2046-513: The Scheme Steering Committee, which oversees the standardization process, announced its intention to recommend splitting Scheme into two languages: a large modern programming language for programmers; and a small version, a subset of the large version retaining the minimalism praised by educators and casual implementors. Two working groups were created to work on these two new versions of Scheme. The Scheme Reports Process site has links to

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2112-582: The United States government. On February 26, 2022, the chair of the IEEE Ukraine Section, Ievgen Pichkalov, publicly appealed to the IEEE members to "freeze [IEEE] activities and membership in Russia" and requested "public reaction and strict disapproval of Russia's aggression" from the IEEE and IEEE Region 8. On March 17, 2022, an article in the form of Q&A interview with IEEE Russia (Siberia) senior member Roman Gorbunov titled "A Russian Perspective on

2178-608: The War in Ukraine" was published in IEEE Spectrum to demonstrate "the plurality of views among IEEE members" and the "views that are at odds with international reporting on the war in Ukraine". On March 30, 2022, activist Anna Rohrbach created an open letter to the IEEE in an attempt to have them directly address the article, stating that the article used "common narratives in Russian propaganda" on

2244-448: The authors' use of the ITS operating system , which limited filenames to two components of at most six characters each. Currently, "Schemer" is commonly used to refer to a Scheme programmer. A new language standardization process began at the 2003 Scheme workshop, with the goal of producing an R6RS standard in 2006. This process broke with the earlier R n RS approach of unanimity. R6RS features

2310-486: The concept of the lexical closure (on page 21), which had been described in an AI Memo in 1970 by Joel Moses , who attributed the idea to Peter J. Landin . Alonzo Church 's mathematical notation, the lambda calculus, has inspired Lisp's use of "lambda" as a keyword for introducing a procedure, as well as influencing the development of functional programming techniques involving the use of higher-order functions in Lisp. But early Lisps were not suitable expressions of

2376-567: The content from several hundred annual conferences sponsored by the IEEE are available in the IEEE Electronic Library (IEL) available through IEEE Xplore platform, for subscription-based access and individual publication purchases. In addition to journals and conference proceedings, the IEEE also publishes tutorials and standards that are produced by its standardization committees. The organization also has its own IEEE paper format. IEEE has 39 technical societies, each focused on

2442-452: The exactness of a number. inexact->exact produces "the exact number that is numerically closest to the argument". exact->inexact produces "the inexact number that is numerically closest to the argument". The R6RS standard omits these procedures from the main report, but specifies them as R5RS compatibility procedures in the standard library (rnrs r5rs (6)). In the R5RS standard, Scheme implementations are not required to implement

2508-521: The fields without traversing the whole fields list that are saved in the RTD. RTD allows users to expand the basic RTD to create a new record system. R6RS introduces numerous significant changes to the language. The source code is now specified in Unicode , and a large subset of Unicode characters may now appear in Scheme symbols and identifiers , and there are other minor changes to the lexical rules. Character data

2574-466: The first of the Lambda Papers, and in subsequent papers, they proceeded to demonstrate the raw power of this practical use of lambda calculus. Scheme inherits its block structure from earlier block structured languages, particularly ALGOL . In Scheme, blocks are implemented by three binding constructs : let , let* and letrec . For instance, the following construct creates a block in which

2640-428: The format of the language itself is as a data format). A typical demonstration of homoiconicity is the meta-circular evaluator . All Von Neumann architecture systems, which includes the vast majority of general purpose computers today, can implicitly be described as homoiconic due to the way that raw machine code executes in memory, the data type being bytes in memory. However, this feature can also be abstracted to

2706-464: The lambda calculus because of their treatment of free variables . A formal lambda system has axioms and a complete calculation rule. It is helpful for the analysis using mathematical logic and tools. In this system, calculation can be seen as a directional deduction. The syntax of lambda calculus follows the recursive expressions from x, y, z, ...,parentheses, spaces, the period and the symbol λ. The function of lambda calculation includes: First, serve as

Scheme (programming language) - Misplaced Pages Continue

2772-496: The language, including those features that distinguish Scheme from other Lisps. Unless stated otherwise, descriptions of features relate to the R5RS standard. In examples provided in this section, the notation "===> result" is used to indicate the result of evaluating the expression on the immediately preceding line. This is the same convention used in R5RS. Scheme is a very simple language, much easier to implement than many other languages of comparable expressive power . This ease

2838-457: The main design goals was that the input script of TRAC (what is typed in by the user) should be identical to the text which guides the internal action of the TRAC processor. In other words, TRAC procedures should be stored in memory as a string of characters exactly as the user typed them at the keyboard. If the TRAC procedures themselves evolve new procedures, these new procedures should also be stated in

2904-405: The minimalism of Scheme was not a conscious design goal, but rather the unintended outcome of the design process. "We were actually trying to build something complicated and discovered, serendipitously, that we had accidentally designed something that met all our goals but was much simpler than we had intended....we realized that the lambda calculus—a small, simple formalism—could serve as the core of

2970-549: The named let is a first-class object. Scheme has an iteration construct, do , but it is more idiomatic in Scheme to use tail recursion to express iteration . Standard-conforming Scheme implementations are required to optimize tail calls so as to support an unbounded number of active tail calls (R5RS sec. 3.5)—a property the Scheme report describes as proper tail recursion —making it safe for Scheme programmers to write iterative algorithms using recursive structures, which are sometimes more intuitive. Tail recursive procedures and

3036-568: The other string), both talk to the user with one language, and both are "homoiconic" in that their internal and external representations are essentially the same. They both have the ability to dynamically create new functions which may then be elaborated at the users's pleasure. Their only great drawback is that programs written in them look like King Burniburiach 's letter to the Sumerians done in Babylonian cuniform! [...] One advantage of homoiconicity

3102-516: The primitive Lisp function LIST and set the variable EXPRESSION to the result Change the COS term to SIN Evaluate the expression Print the expression to a string Read the expression from a string On line 4 we create a new clause. The operator :- separates the head and the body of a clause. With assert/1 * we add it to the existing clauses (add it to the "database"), so we can call it later. In other languages we would call it "creating

3168-529: The primitive Lisp function READ . READ returns Lisp data: lists, symbols , numbers, strings. The primitive Lisp function EVAL uses Lisp code represented as Lisp data, computes side-effects and returns a result. The result will be printed by the primitive function PRINT , which creates an external S-expression from Lisp data. Lisp data, a list using different data types: (sub)lists, symbols, strings and integer numbers. Lisp code. The example uses lists, symbols and numbers. Create above expression with

3234-417: The processing costs associated with the primitive textual substitution methods used to implement lexical scoping algorithms in compilers and interpreters of the day. In those Lisps, it was perfectly possible for a reference to a free variable inside a procedure to refer to quite distinct bindings external to the procedure, depending on the context of the call. The impetus to incorporate lexical scoping, which

3300-438: The program's entities at runtime ) depends on a single, homogeneous structure, and it does not have to handle several different structures that would appear in a complex syntax. Homoiconic languages typically include full support of syntactic macros , allowing the programmer to express transformations of programs in a concise way. A commonly cited example is Lisp , which was created to allow for easy list manipulations and where

3366-408: The programmer to create non-local control constructs such as iterators , coroutines , and backtracking . Continuations can be used to emulate the behavior of return statements in imperative programming languages. The following function find-first , given function func and list lst , returns the first element x in lst such that (func x) returns true. The following example,

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3432-641: The programming language level. Languages such as Lisp and its dialects, such as Scheme , Clojure , and Racket employ S-expressions to achieve homoiconicity, and are considered the "Purest" forms of homoiconicity, as these languages use the same representation for both data and code. Other languages provide data structures for easily and efficiently manipulating code. Notable examples of this weaker form of homoiconicity include Julia , Nim , and Elixir . Languages often considered to be homoiconic include: Lisp uses S-expressions as an external representation for data and code. S-expressions can be read with

3498-421: The property arises from the fact that, strictly, this applies to almost all programming languages. No consensus exists on a precise definition of the property. In a homoiconic language, the primary representation of programs is also a data structure in a primitive type of the language itself. This makes metaprogramming easier than in a language without this property: reflection in the language (examining

3564-437: The proposed implicitly phased libraries for R6RS, called psyntax, which loads and bootstraps itself properly on various older Scheme implementations. A feature of R6RS is the record-type descriptor (RTD). When an RTD is created and used, the record type representation can show the memory layout. It also calculated object field bit mask and mutable Scheme object field bit masks, and helped the garbage collector know what to do with

3630-406: The quality of exactness. An exact number can only be produced by a sequence of exact operations involving other exact numbers—inexactness is thus contagious. The standard specifies that any two implementations must produce equivalent results for all operations resulting in exact numbers. The R5RS standard specifies procedures exact->inexact and inexact->exact which can be used to change

3696-413: The same script. The TRAC processor in its action interprets this script as its program. In other words, the TRAC translator program (the processor) effectively converts the computer into a new computer with a new program language -- the TRAC language. At any time, it should be possible to display program or procedural information in the same form as the TRAC processor will act upon it during its execution. It

3762-564: The structure is given by S-expressions that take the form of nested lists, and can be manipulated by other Lisp code. Other examples are the programming languages Clojure (a contemporary dialect of Lisp), Rebol (also its successor Red ), Refal , Prolog , and possibly Julia (see the section “Implementation methods” for more details). The term first appeared in connection with the TRAC programming language , developed by Calvin Mooers : One of

3828-497: The term "icon" in his Semiotic Theory. According to Peirce, there are three kinds of sign in communication: the icon, the index and the symbol. The icon is the simplest representation: an icon physically resembles that which it denotes. Alan Kay used and possibly popularized the term "homoiconic" through his use of the term in his 1969 PhD thesis: A notable group of exceptions to all the previous systems are Interactive LISP [...] and TRAC. Both are functionally oriented (one list,

3894-468: The timeline below reflects the chronological order of ratification. Scheme started in the 1970s as an attempt to understand Carl Hewitt 's Actor model , for which purpose Steele and Sussman wrote a "tiny Lisp interpreter" using Maclisp and then "added mechanisms for creating actors and sending messages". Scheme was originally called "Schemer", in the tradition of other Lisp -derived languages such as Planner or Conniver . The current name resulted from

3960-402: The type block! and can furthermore be assigned as the value of a word by using what appears to be a syntax for assignment, but is actually understood by the interpreter as a special type ( set-word! ) and takes the form of a word followed by a colon: The block can still be interpreted by using the do function provided in Rebol (similar to eval in Lisp ). It is possible to interrogate

4026-465: The use of all of Scheme at macro expansion time. Compliant implementations are now required to support Scheme's full numeric tower , and the semantics of numbers have been expanded, mainly in the direction of support for the IEEE 754 standard for floating point numerical representation. The R6RS standard has caused controversy because some see it as a departure from the minimalist philosophy. In August 2009,

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4092-791: The whole numerical tower, but they must implement "a coherent subset consistent with both the purposes of the implementation and the spirit of the Scheme language" (R5RS sec. 6.2.3). The new R6RS standard does require implementation of the whole tower, and "exact integer objects and exact rational number objects of practically unlimited size and precision, and to implement certain procedures...so they always return exact results when given exact arguments" (R6RS sec. 3.4, sec. 11.7.1). Example 1: exact arithmetic in an implementation that supports exact rational complex numbers. Example 2: Same arithmetic in an implementation that supports neither exact rational numbers nor complex numbers but does accept real numbers in rational notation. Both implementations conform to

4158-402: The working groups' charters, public discussions and issue tracking system. The ninth draft of R7RS (small language) was made available on April 15, 2013. A vote ratifying this draft closed on May 20, 2013, and the final report has been available since August 6, 2013, describing "the 'small' language of that effort: therefore it cannot be considered in isolation as the successor to R6RS". Scheme

4224-429: The years which have given Scheme a particular character, but are not the direct outcomes of the original design. Scheme specifies a comparatively full set of numerical datatypes including complex and rational types, which is known in Scheme as the numerical tower (R5RS sec. 6.2). The standard treats these as abstractions, and does not commit the implementor to any particular internal representations. Numbers may have

4290-526: Was an unusual scoping model in the early 1970s, into their new version of Lisp, came from Sussman's studies of ALGOL . He suggested that ALGOL-like lexical scoping mechanisms would help to realize their initial goal of implementing Hewitt's Actor model in Lisp. The key insights on how to introduce lexical scoping into a Lisp dialect were popularized in Sussman and Steele's 1975 Lambda Paper, "Scheme: An Interpreter for Extended Lambda Calculus", where they adopted

4356-553: Was necessary for this purpose, and the scope was broadened. In addition to soliciting and administering unrestricted funds, the foundation also administers donor-designated funds supporting particular educational, humanitarian, historical preservation, and peer recognition programs of the IEEE. As of the end of 2014, the foundation's total assets were nearly $ 45 million, split equally between unrestricted and donor-designated funds. In May 2019, IEEE restricted Huawei employees from peer reviewing papers or handling papers as editors due to

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