Invocations of macros and procedures bear a close resemblance—both are s-expressions—but they are treated differently. When the compiler encounters an s-expression in the program, it first checks to see if the symbol is defined as a syntactic keyword within the current lexical scope. If so, it then attempts to expand the macro, treating the items in the tail of the s-expression as arguments without compiling code to evaluate them, and this process is repeated recursively until no macro invocations remain. If it is not a syntactic keyword, the compiler compiles code to evaluate the arguments in the tail of the s-expression and then to evaluate the variable represented by the symbol at the head of the s-expression and call it as a procedure with the evaluated tail expressions passed as actual arguments to it.

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1660s, from French fond "a bottom, floor, ground" (12c.), also "a merchant's basic stock or capital," from Latin fundus "bottom, foundation, piece of land," from PIE root *bhudh- "bottom, base" (cf. Sanskrit budhnah, Greek pythmen "foundation, bottom," Old English botm "lowest part;" see bottom (n.)). Funds "money at one's disposal" is from 1728. Fund-raiser (also fundraiser) first attested 1957.

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The elegant, minimalist design has made Scheme a popular target for language designers, hobbyists, and educators, and because of its small size, that of a typical interpreter, it is also a popular choice for embedded systems and scripting. This has resulted in scores of implementations,[35] most of which differ from each other so much that porting programs from one implementation to another is quite difficult, and the small size of the standard language means that writing a useful program of any great complexity in standard, portable Scheme is almost impossible.[7] The R6RS standard specifies a much broader language, in an attempt to broaden its appeal to programmers.

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1550s, "figure of speech," from Medieval Latin schema "shape, figure, form, appearance; figure of speech; posture in dancing," from Greek skhema (genitive skhematos) "figure, appearance, the nature of a thing," related to skhein "to get," and ekhein "to have," from PIE root *segh- "to hold, to hold in one's power, to have" (cf. Sanskrit sahate "he masters, overcomes," sahah "power, victory;" Avestan hazah "power, victory;" Greek ekhein "to have, hold;" Gothic sigis, Old High German sigu, Old Norse sigr, Old English sige "victory").

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^ Joel Moses (June 1970), The Function of FUNCTION in LISP, or Why the FUNARG Problem Should Be Called the Environment Problem, hdl:1721.1/5854, AI Memo 199, A useful metaphor for the difference between FUNCTION and QUOTE in LISP is to think of QUOTE as a porous or an open covering of the function since free variables escape to the current environment. FUNCTION acts as a closed or nonporous covering (hence the term "closure" used by Landin). Thus we talk of "open" Lambda expressions (functions in LISP are usually Lambda expressions) and "closed" Lambda expressions. [...] My interest in the environment problem began while Landin, who had a deep understanding of the problem, visited MIT during 1966-67. I then realized the correspondence between the FUNARG lists which are the results of the evaluation of "closed" Lambda expressions in LISP and ISWIM's Lambda Closures.

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The R6RS standard has caused controversy because it is seen to have departed from the minimalist philosophy.[13][14] In August 2009, 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.[7] Two working groups were created to work on these two new versions of Scheme. The Scheme Reports Process site has links to the working groups' charters, public discussions and issue tracking system.

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The information on this computer and network is the property of a private corporation and is protected by intellectual property rights. You must be assigned an account on this computer to access information and are only allowed to access information as defined by the system administrators. Use of company resources should be for business purposes only and should be in compliance with the Code of Conduct and company policies and procedures. By accessing the property of a private corporation, your activities may be monitored and/or recorded and you should have no expectation of privacy on this computer and its networks. Use of this computer implies consent to monitoring and recording.

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The introduction of lexical scope resolved the problem by making an equivalence between some forms of lambda notation and their practical expression in 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".[23] They introduced continuation-passing style along with their first description of Scheme in the first of the Lambda Papers, and in subsequent papers, they proceeded to demonstrate the raw power of this practical use of lambda calculus.

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The introduction of lexical scope resolved the problem by making an equivalence between some forms of lambda notation and their practical expression in 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".[23] They introduced continuation-passing style along with their first description of Scheme in the first of the Lambda Papers, and in subsequent papers, they proceeded to demonstrate the raw power of this practical use of lambda calculus. 

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The Scheme language is standardized in the official IEEE standard[3] and a de facto standard called the Revisedn Report on the Algorithmic Language Scheme (RnRS). The most widely implemented standard is R5RS (1998);[4] a new standard, R6RS,[5] was ratified in 2007.[6] Scheme has a diverse user base due to its compactness and elegance, but its minimalist philosophy has also caused wide divergence between practical implementations, so much that the Scheme Steering Committee calls it "the world's most unportable programming language" and "a family of dialects" rather than a single language.[7]

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Almost all implementations provide a traditional Lisp-style read–eval–print loop for development and debugging. Many also compile Scheme programs to executable binary. Support for embedding Scheme code in programs written in other languages is also common, as the relative simplicity of Scheme implementations makes it a popular choice for adding scripting capabilities to larger systems developed in languages such as C. The Gambit, Chicken, and Bigloo Scheme interpreters compile Scheme to C, which makes embedding particularly easy. In addition, Bigloo's compiler can be configured to generate JVM bytecode, and it also features an experimental bytecode generator for .NET.

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Some implementations support additional features. For example, Kawa and JScheme provide integration with Java classes, and the Scheme to C compilers often make it easy to use external libraries written in C, up to allowing the embedding of actual C code in the Scheme source. Another example is Pvts, which offers a set of visual tools for supporting the learning of Scheme.

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These meditations were entirely employed on Mr Allworthy's fortune; for, first, he exercised much thought in calculating, as well as he could, the exact value of the whole: which calculations he often saw occasion to alter in his own favour: and, secondly and chiefly, he pleased himself with intended alterations in the house and gardens, and in projecting many other schemes, as well for the improvement of the estate as of the grandeur of the place: for this purpose he applied himself to the studies of architecture and gardening, and read over many books on both these subjects; for these sciences, indeed, employed his whole time, and formed his only amusement.

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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 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.

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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",[19] where they adopted 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.[20]

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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.[21] The function of lambda calculation includes: First, serve as a starting point of powerful mathematical logic. Second, it can reduce the requirement of programmers to consider the implementation details, because it can use for imitate machine evaluation. Finally, the lambda calculation created a substantial meta-theory.[22]

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The elegant, minimalist design has made Scheme a popular target for language designers, hobbyists, and educators, and because of its small size, that of a typical interpreter, it is also a popular choice for embedded systems and scripting. This has resulted in scores of implementations,[35] most of which differ from each other so much that porting programs from one implementation to another is quite difficult, and the small size of the standard language means that writing a useful program of any great complexity in standard, portable Scheme is almost impossible.[7] The R6RS standard specifies a much broader language, in an attempt to broaden its appeal to programmers.

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Scheme is widely used by a number[37] of schools; in particular, a number of introductory Computer Science courses use Scheme in conjunction with the textbook Structure and Interpretation of Computer Programs (SICP).[38] For the past 12 years, PLT has run the ProgramByDesign (formerly TeachScheme!) project, which has exposed close to 600 high school teachers and thousands of high school students to rudimentary Scheme programming. MIT's old introductory programming class 6.001 was taught in Scheme,[39] Although 6.001 has been replaced by more modern courses, SICP continues to be taught at MIT.[40] The textbook How to Design Programs by Matthias Felleisen, currently at Northeastern University, is used by some institutes of higher education for their introductory computer science courses. Both Northeastern University and Worcester Polytechnic Institute use Scheme exclusively for their introductory courses Fundamentals of Computer Science (CS2500) and Introduction to Program Design (CS1101), respectively.[41][42] Rose-Hulman uses Scheme in its more advanced Programming Language Concepts course.[43] Indiana University's introductory class, C211, is taught entirely in Scheme. The introductory class at UC Berkeley, CS 61A, was until 2015 taught entirely in Scheme, save minor diversions into Logo to demonstrate dynamic scope; all course materials, including lecture webcasts, are available online free of charge.[44] A self-paced version of the course, CS 61AS, continues to use Scheme.[45] The introductory computer science courses at Yale and Grinnell College are also taught in Scheme.[46] Programming Design Paradigms,[47] a mandatory course for the Computer science Graduate Students at Northeastern University, also extensively uses Scheme. The introductory Computer Science course at the University of Minnesota - Twin Cities, CSCI 1901, also uses Scheme as its primary language, followed by a course that introduces students to the Java programming language.[48] In the software industry, Tata Consultancy Services, Asia's largest software consultancy firm, uses Scheme in their month-long training program for fresh college graduates.[citation needed]

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Most Lisps specify an order of evaluation for procedure arguments. Scheme does not. Order of evaluation—including the order in which the expression in the operator position is evaluated—may be chosen by an implementation on a call-by-call basis, and the only constraint is that "the effect of any concurrent evaluation of the operator and operand expressions is constrained to be consistent with some sequential order of evaluation." (R5RS sec. 4.1.3)[4]

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In economics funds are injected into the market as capital by lenders and taken as loans by borrowers. There are two ways in which the capital can end up at the borrower. The lender can lend the capital to a financial intermediary against interest. These financial intermediaries then reinvest the money against a higher rate. The use of financial intermediaries to finance operations is called indirect finance. A lender can also go the financial markets to directly lend to a borrower. This method is called direct finance.[3]

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Implementations of the hygienic macro system, also called syntax-rules, are required to respect the lexical scoping of the rest of the language. This is assured by special naming and scoping rules for macro expansion and avoids common programming errors that can occur in the macro systems of other programming languages. R6RS specifies a more sophisticated transformation system, syntax-case, which has been available as a language extension to R5RS Scheme for some time.

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Scheme 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.

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Full integration with Global Treasury Services' records will be the icing on the cake for the Funding the Mission plan. Pastors, church boards, treasurers, district officers, and other record keepers can log into the Reporting Calculator, enter a few line items, match up previous contributions, check progress toward Ten Percent recognition, and safely and securely transfer funds for World Evangelism.

R5RS resolves this confusion by specifying three procedures that return environments and providing a procedure eval that takes an s-expression and an environment and evaluates the expression in the environment provided. (R5RS sec. 6.5)[4] R6RS extends this by providing a procedure called environment by which the programmer can specify exactly which objects to import into the evaluation environment.

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Up to the R5RS standard, the standard comment in Scheme was a semicolon, which makes the rest of the line invisible to Scheme. Numerous implementations have supported alternative conventions permitting comments to extend for more than a single line, and the R6RS standard permits two of them: an entire s-expression may be turned into a comment (or "commented out") by preceding it with #; (introduced in SRFI 62[29]) and a multiline comment or "block comment" may be produced by surrounding text with #| and |#.

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^ Jump up to: a b 1178-1990 (Reaff 2008) IEEE Standard for the Scheme Programming Language. IEEE part number STDPD14209, unanimously reaffirmed at a meeting of the IEEE-SA Standards Board Standards Review Committee (RevCom), March 26, 2008 (item 6.3 on minutes), reaffirmation minutes accessed October 2009. NOTE: this document is only available for purchase from IEEE and is not available online at the time of writing (2009). 

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Government could allocate funds itself or through government agencies to projects that benefit the public through selection process to students or researchers and even organisations. At least two external peer-reviewers and internal research award committee review each application. The research awards committee would meet some time to discuss shortlisted applications. A further shortlist and ranking is made. Projects are funded and applicants are informed.[7]

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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 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.

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The R6RS standard has caused controversy because it is seen to have departed from the minimalist philosophy.[13][14] In August 2009, 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.[7] Two working groups were created to work on these two new versions of Scheme. The Scheme Reports Process site has links to the working groups' charters, public discussions and issue tracking system.

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The introduction of lexical scope resolved the problem by making an equivalence between some forms of lambda notation and their practical expression in 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".[23] They introduced continuation-passing style along with their first description of Scheme in the first of the Lambda Papers, and in subsequent papers, they proceeded to demonstrate the raw power of this practical use of lambda calculus.

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verb arrange, be cunning, cabal, calculate, chart, collude, complot, compose, concoct, connive, contrive, design, devise, diagram, engineer, fabricate, fashion, frame, hatch, have designs, improvise, intrigue, invent, lay a plan, machinate, make arrangements, maneuver, manipulate, map, map out, outline, plan, plot, predesign, predetermine, prepare, project, ratio, think ahead, think out, weave a plot, work out, work up

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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 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.[11]

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Most Lisps specify an order of evaluation for procedure arguments. Scheme does not. Order of evaluation—including the order in which the expression in the operator position is evaluated—may be chosen by an implementation on a call-by-call basis, and the only constraint is that "the effect of any concurrent evaluation of the operator and operand expressions is constrained to be consistent with some sequential order of evaluation." (R5RS sec. 4.1.3)[4]

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Up to the R5RS standard, the standard comment in Scheme was a semicolon, which makes the rest of the line invisible to Scheme. Numerous implementations have supported alternative conventions permitting comments to extend for more than a single line, and the R6RS standard permits two of them: an entire s-expression may be turned into a comment (or "commented out") by preceding it with #; (introduced in SRFI 62[29]) and a multiline comment or "block comment" may be produced by surrounding text with #| and |#.

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Full integration with Global Treasury Services' records will be the icing on the cake for the Funding the Mission plan. Pastors, church boards, treasurers, district officers, and other record keepers can log into the Reporting Calculator, enter a few line items, match up previous contributions, check progress toward Ten Percent recognition, and safely and securely transfer funds for World Evangelism.

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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 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.[11]

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R5RS resolves this confusion by specifying three procedures that return environments and providing a procedure eval that takes an s-expression and an environment and evaluates the expression in the environment provided. (R5RS sec. 6.5)[4] R6RS extends this by providing a procedure called environment by which the programmer can specify exactly which objects to import into the evaluation environment.

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Crowdfunding exists in mainly two types, reward-based crowdfunding and equity-based crowdfunding. In the former, small firms could pre-sell a product or service to start a business whereas in the latter, backers buys certain amount of shares of a firm in exchange of money.[8] As for reward-based crowdfunding, project creators would set a funding target and deadline. Anyone who is interested can pledge on the projects. Projects must reach its targeted amount in order for it to be carried out. Once the projects ended with enough funds, projects creators would have to make sure that they fulfil their promises by the intended timeline and delivery their products or services.[9]

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R5RS resolves this confusion by specifying three procedures that return environments and providing a procedure eval that takes an s-expression and an environment and evaluates the expression in the environment provided. (R5RS sec. 6.5)[4] R6RS extends this by providing a procedure called environment by which the programmer can specify exactly which objects to import into the evaluation environment.

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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 the lambda calculus because of their treatment of free variables.[8]

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Invocations of macros and procedures bear a close resemblance—both are s-expressions—but they are treated differently. When the compiler encounters an s-expression in the program, it first checks to see if the symbol is defined as a syntactic keyword within the current lexical scope. If so, it then attempts to expand the macro, treating the items in the tail of the s-expression as arguments without compiling code to evaluate them, and this process is repeated recursively until no macro invocations remain. If it is not a syntactic keyword, the compiler compiles code to evaluate the arguments in the tail of the s-expression and then to evaluate the variable represented by the symbol at the head of the s-expression and call it as a procedure with the evaluated tail expressions passed as actual arguments to it.

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1550s, "figure of speech," from Medieval Latin schema "shape, figure, form, appearance; figure of speech; posture in dancing," from Greek skhema (genitive skhematos) "figure, appearance, the nature of a thing," related to skhein "to get," and ekhein "to have," from PIE root *segh- "to hold, to hold in one's power, to have" (cf. Sanskrit sahate "he masters, overcomes," sahah "power, victory;" Avestan hazah "power, victory;" Greek ekhein "to have, hold;" Gothic sigis, Old High German sigu, Old Norse sigr, Old English sige "victory").

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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)[4] First-class continuations enable the programmer to create non-local control constructs such as iterators, coroutines, and backtracking.

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It is used for research, in fields of technology or social science. Research funding can split into commercial and non-commercial. Research and development departments of a corporation normally provide commercial research funding. Whereas, non-commercial research funding is obtained from charities, research councils, or government agencies.[4] Organisations that require such funding normally have to go through competitive selections. Only those that have the most potential would be chosen. Funding is vital in ensuring the sustainability of certain projects. 

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In the R5RS standard and also in later reports, the syntax of Scheme can easily be extended via the macro system. The R5RS standard introduced a powerful hygienic macro system that allows the programmer to add new syntactic constructs to the language using a simple pattern matching sublanguage (R5RS sec 4.3).[4] Prior to this, the hygienic macro system had been relegated to an appendix of the R4RS standard, as a "high level" system alongside a "low level" macro system, both of which were treated as extensions to Scheme rather than an essential part of the language.[26]

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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 the lambda calculus because of their treatment of free variables.[8]

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It is used for research, in fields of technology or social science. Research funding can split into commercial and non-commercial. Research and development departments of a corporation normally provide commercial research funding. Whereas, non-commercial research funding is obtained from charities, research councils, or government agencies.[4] Organisations that require such funding normally have to go through competitive selections. Only those that have the most potential would be chosen. Funding is vital in ensuring the sustainability of certain projects.
Scheme 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.

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Entrepreneurs with a business concept would want to accumulate all the necessary resources including capital to venture into a market. Funding is part of the process, as some businesses would require large start-up sums that individuals would not have.[5] These start-up funds are essential to kick-start a business idea, without it, entrepreneurs would not have the ability to carry out their concepts in the business world.

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The R6RS standard has caused controversy because it is seen to have departed from the minimalist philosophy.[13][14] In August 2009, 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.[7] Two working groups were created to work on these two new versions of Scheme. The Scheme Reports Process site has links to the working groups' charters, public discussions and issue tracking system.

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Guile has been adopted by GNU project as its official scripting language, and that implementation of Scheme is embedded in such applications as GNU LilyPond and GnuCash as a scripting language for extensions. Likewise, Guile used to be the scripting language for the desktop environment GNOME,[51] and GNOME still has a project that provides Guile bindings to its library stack.[52] There is a project to incorporate Guile into GNU Emacs, GNU's flagship program, replacing the current Emacs Lisp interpreter.[citation needed]

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Chez scheme is a notable example for individual type of implementation of Scheme, it was created by R. Kent Dybvig in 1985. Chez Scheme includes completely different implementation of Scheme, which could replace some of the functions of Racket. Chez scheme has a relatively different core part in distribution. As a result, the application of Chez scheme can make every Racket runs magically fast.[36] 

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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 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.

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R5RS resolves this confusion by specifying three procedures that return environments and providing a procedure eval that takes an s-expression and an environment and evaluates the expression in the environment provided. (R5RS sec. 6.5)[4] R6RS extends this by providing a procedure called environment by which the programmer can specify exactly which objects to import into the evaluation environment.

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These meditations were entirely employed on Mr Allworthy's fortune; for, first, he exercised much thought in calculating, as well as he could, the exact value of the whole: which calculations he often saw occasion to alter in his own favour: and, secondly and chiefly, he pleased himself with intended alterations in the house and gardens, and in projecting many other schemes, as well for the improvement of the estate as of the grandeur of the place: for this purpose he applied himself to the studies of architecture and gardening, and read over many books on both these subjects; for these sciences, indeed, employed his whole time, and formed his only amusement.

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The Scheme language is standardized in the official IEEE standard[3] and a de facto standard called the Revisedn Report on the Algorithmic Language Scheme (RnRS). The most widely implemented standard is R5RS (1998);[4] a new standard, R6RS,[5] was ratified in 2007.[6] Scheme has a diverse user base due to its compactness and elegance, but its minimalist philosophy has also caused wide divergence between practical implementations, so much that the Scheme Steering Committee calls it "the world's most unportable programming language" and "a family of dialects" rather than a single language.[7]
^ Jump up to: a b 1178-1990 (Reaff 2008) IEEE Standard for the Scheme Programming Language. IEEE part number STDPD14209, unanimously reaffirmed at a meeting of the IEEE-SA Standards Board Standards Review Committee (RevCom), March 26, 2008 (item 6.3 on minutes), reaffirmation minutes accessed October 2009. NOTE: this document is only available for purchase from IEEE and is not available online at the time of writing (2009).

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The R6RS standard has caused controversy because it is seen to have departed from the minimalist philosophy.[13][14] In August 2009, 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.[7] Two working groups were created to work on these two new versions of Scheme. The Scheme Reports Process site has links to the working groups' charters, public discussions and issue tracking system.

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Because of Scheme's minimalism, many common procedures and syntactic forms are not defined by the standard. In order to keep the core language small but facilitate standardization of extensions, the Scheme community has a "Scheme Request for Implementation" (SRFI) process by which extension libraries are defined through careful discussion of extension proposals. This promotes code portability. Many of the SRFIs are supported by all or most Scheme implementations.

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Chez scheme is a notable example for individual type of implementation of Scheme, it was created by R. Kent Dybvig in 1985. Chez Scheme includes completely different implementation of Scheme, which could replace some of the functions of Racket. Chez scheme has a relatively different core part in distribution. As a result, the application of Chez scheme can make every Racket runs magically fast.[36]

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