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R6RS introduces numerous significant changes to the language.<ref name="r6rs_Language_changes">{{Cite web |date=2007-09-26 |title=Revised^6 Report on the Algorithmic Language Scheme, Appendix E: language changes |url=http://www.r6rs.org/final/html/r6rs/r6rs-Z-H-19.html#node_chap_E |access-date=2009-10-20 |publisher=Scheme Steering Committee}}</ref> The source code is now specified in [[Unicode]], and a large subset of Unicode characters may now appear in Scheme symbols and [[identifier]]s, and there are other minor changes to the lexical rules. Character data 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 the use of all of Scheme at macro expansion time. Compliant implementations are now ''required'' to support Scheme's full [[Numerical tower|numeric tower]], and the semantics of numbers have been expanded, mainly in the direction of support for the [[IEEE 754-1985|IEEE 754]] standard for floating point numerical representation.
===R7RS===
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This section concentrates mainly on innovative features of 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.
===Minimalism===
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{{See also|Scope (programming)}}
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.
The impetus to incorporate lexical scoping, which 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 [[Block (programming)|ALGOL-like lexical scoping mechanisms]] would help to realize their initial goal of implementing [[Carl Hewitt#Actor model|Hewitt's Actor model]] in Lisp.<ref name="revisited"/>
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== Usage ==
Scheme is widely used by several<ref name="schemers_inc">{{Cite web |last=Ed Martin |date=2009-07-20 |title=List of Scheme-using schools |url=http://www.schemers.com/schools.html |access-date=2009-10-20 |publisher=Schemers Inc.}}</ref> schools; in particular, several introductory [[computer science]] courses use Scheme in conjunction with the textbook ''[[Structure and Interpretation of Computer Programs]]'' (SICP).<ref name="sicp_adopters">{{Cite web |date=1999-01-26 |title=List of SICP-using schools |url=http://mitpress.mit.edu/sicp/adopt-list.html |access-date=2009-10-20 |publisher=MIT Press}}</ref> For the past 12 years, [[Racket (programming language)|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,<ref name="6.001">{{Cite web |last=Eric Grimson |author-link=Eric Grimson |date=Spring 2005 |title=6.001 Structure and Interpretation of Computer Programs |url=http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-001Spring-2005/CourseHome/index.htm |access-date=2009-10-20 |publisher=MIT Open Courseware}}</ref> Although 6.001 has been replaced by more modern courses, SICP continues to be taught at MIT.<ref name="6.001_zombies">{{Cite web |last1=Alex Vandiver |last2=Nelson Elhage |display-authors=etal |date=January 2009 |title=6.184 - Zombies drink caffeinated 6.001 |url=http://web.mit.edu/alexmv/6.001/ |access-date=2009-10-20 |publisher=MIT CSAIL}}</ref> Likewise, the introductory class at [[UC Berkeley]], CS 61A, was until 2011 taught entirely in Scheme, save minor diversions into [[Logo (programming language)|Logo]] to demonstrate dynamic scope. Today, like MIT, Berkeley has replaced the syllabus with a more modern version that is primarily taught in [[Python (programming language)|Python 3]], but the current syllabus is still based on the old curriculum, and parts of the class are still taught in Scheme.<ref name="61A">{{Cite web |last=John DeNero |date=Fall 2019 |title=Computer Science 61A, Berkeley |url=https://cs61a.org/articles/about.html |access-date=2019-12-17 |publisher=Department of Electrical Engineering and Computer Sciences, Berkeley}}</ref>
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.<ref name="neu">[http://www.ccs.neu.edu/course/cs2500/ CS 2500: Fundamentals of Computer Science I], [[Northeastern University]]</ref><ref name="wpi">[http://web.cs.wpi.edu/~cs1101/a05/details.html#software CS 1101: Introduction to Program Design (A05): course software], [[Worcester Polytechnic Institute]]</ref> [[Rose-Hulman]] uses Scheme in its more advanced Programming Language Concepts course.<ref name="rhit">{{Cite web |title=CSSE 304: Programming Language Concepts |url=https://www.rose-hulman.edu/Users/faculty/young/CS-Classes/csse304/syllabus.html |publisher=[[Rose-Hulman Institute of Technology]]}}</ref> [[Brandeis University]]'s core course, Structure and Interpretations of Computer Programs (COSI121b), is also taught exclusively in Scheme by theoretical computer scientist [[Harry Mairson]].<ref name="brandeis">{{Cite web |title=Spring 2021 CS121b Syllabus |url=https://moodle2.brandeis.edu/syllabus/public/1202dcdfe19c0860e226f6447f66875c.pdf |publisher=[[Brandeis University]]}}</ref> [[Indiana University]]'s introductory class, C211, is taught entirely in Scheme. A self-paced version of the course, CS 61AS, continues to use Scheme.<ref>{{cite web |url=https://berkeley-cs61as.github.io/ |title=Home |website=berkeley-cs61as.github.io}}</ref> The introductory computer science courses at [[Yale]] and [[Grinnell College]] are also taught in Scheme.<ref name="yale_cs201">{{Cite web |last=Dana Angluin |date=Fall 2009 |title=Introduction to Computer Science (CPSC 201) |url=http://zoo.cs.yale.edu/classes/cs201/ |access-date=2009-10-20 |publisher=The Zoo, Yale University Computer Science Department}}</ref> Programming Design Paradigms,<ref name="neu2">{{Cite web |date=Fall 2009 |title=Programming Design Paradigms CSG107 Course Readings |url=http://www.ccs.neu.edu/home/matthias/107-f08/readings.html |access-date=2012-08-09 |publisher=Northeastern University College of Computer and Information Science}}</ref> a mandatory course for the Computer science Graduate Students at [[Northeastern University]], also extensively uses Scheme.
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