Scheme (programming language): Difference between revisions

Revision as of 06:44, 30 December 2022

Revision as of 19:24, 28 January 2023

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Currently the newest releases of various Scheme implementations<ref name="rs6s_Implementations">{{Cite web |title=R6RS Implementations |url=http://www.r6rs.org/implementations.html |access-date=2017-11-24 |publisher=r6rs.org}}</ref> support the R6RS standard. There is a portable reference implementation of the proposed implicitly phased libraries for R6RS, called psyntax, which loads and bootstraps itself properly on various older Scheme implementations.<ref name="psyntax">{{Cite web |last=Abdulaziz Ghuloum |date=2007-10-27 |title=R6RS Libraries and syntax-case system (psyntax) |url=https://www.cs.indiana.edu/~aghuloum/r6rs-libraries/ |access-date=2009-10-20 |publisher=Ikarus Scheme}}</ref>

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.<ref>{{Cite journal |last=Keep |first=Andrew W. |last2=Dybvig |first2=R. Kent |date=November 2014 |title=A run-time representation of scheme record types |journal=Journal of Functional Programming |volume=24 |issue=6 |pages=675–716 |doi=10.1017/S0956796814000203 |s2cid=40001845|doi-access=free }}</ref>

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.