History of the Scheme programming language: Difference between revisions

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The history of the programming language [[Scheme (programming language)|Scheme]] begins with the development of earlier members of the [[Lisp (programming language)|Lisp]] family of languages during the second half of the twentieth century. During the design and development period of Scheme, language designers [[Guy L. Steele]] and [[Gerald Jay Sussman]] released an influential series of [[Massachusetts Institute of Technology]] (MIT) [[AI Memo]]s known as the ''[[Lambda Papers]]'' (1975–1980). This resulted in the growth of popularity in the language and the era of standardization from 1990 onward. Much of the history of Scheme has been documented by the developers themselves.<ref name="steele_history">{{cite web |url=http://www-mips.unice.fr/~roy/JAOO-SchemeHistory-2006public.pdf |title=History of Scheme |last=Steele |first=Guy |date=2006 |website=Sun Microsystems Laboratories |format=PDF slideshow |access-date=2023-04-05 |archive-date=2023-03-02 |archive-url=https://web.archive.org/web/20230302184733/http://www-mips.unice.fr/~roy/JAOO-SchemeHistory-2006public.pdf |url-status=bot: unknown }}</ref>

==Prehistory==

{{Expand section|date=January 2011}}

The development of Scheme was heavily influenced by two predecessors that were quite different from one another: [[Lisp (programming language)|Lisp]] provided its general semantics and syntax, and [[ALGOL]] provided its [[Scope (computer science)|lexical scope]] and block structure. Scheme is a dialect of Lisp but Lisp has evolved; the Lisp dialects from which Scheme evolved—although they were in the mainstream at the time—are quite different from any modern Lisp. Scheme falls within the large Lisp family of languages that includes Common Lisp, Scheme, ISLisp, EuLisp, XLisp, and AutoLisp.

===Lisp===

{{detailsfurther|Lisp (programming language)}}

Lisp was invented by [[John McCarthy (computer scientist)|John McCarthy]] in 1958 while he was at the [[Massachusetts Institute of Technology]] (MIT). McCarthy published its design in a paper in ''[[Communications of the ACM]]'' in 1960, entitled "Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I"<ref name="McCarthy">{{cite web |url=http://www-formal.stanford.edu/jmc/recursive.html |title=Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I |last=McCarthy |first=John |author-link=John McCarthy (computer scientist) |access-date=2006-10-13 |archive-url=https://web.archive.org/web/20131004215327/http://www-formal.stanford.edu/jmc/recursive.html |archive-date=2013-10-04 |url-status=dead }}</ref> (Part II was never published). He showed that with a few simple operators and a notation for functions, one can build a [[Turing-complete]] language for algorithms.

The use of [[s-expression]]s which characterize the syntax of Lisp was initially intended to be an interim measure pending the development of a language employing what McCarthy called "[[m-expression]]s". As an example, the m-expression <code>car[cons[A,B]]</code> is equivalent to the s-expression <code>{{Nowrap|(car (cons A B))}}</code>. S-expressions proved popular, however, and the many attempts to implement m-expressions failed to catch on.

The first implementation of Lisp was on an [[IBM 704]] by [[Steve Russell (computer scientist)|Steve Russell]], who read McCarthy's paper and coded the eval function he described in machine code. The familiar (but puzzling to newcomers) names [[CAR and CDR]] used in Lisp to describe the head element of a list and its tail, evolved from two [[IBM 704]] assembly language commands: Contents of Address Register and Contents of Decrement Register, each of which returned the contents of a 15-bit register corresponding to segments of a [[36-bit computing|36-bit]] IBM &nbsp;704 instruction [[Wordword (computer architecture)|word]].

The first complete Lisp compiler, written in Lisp, was implemented in 1962 by Tim Hart and Mike Levin at MIT.<ref name="Levin">{{cite web |url=ftp://publications.ai.mit.edu/ai-publications/pdf/AIM-039.pdf |title=AI Memo 39, The New Compiler |lastlast1=Hart |firstfirst1=Tim |last2=Levin |first2=Mike |accessarchive-dateurl=2006https://web.archive.org/web/20170706114742/ftp://publications.ai.mit.edu/ai-10publications/pdf/AIM-13039.pdf }}{{Dead link|archive-date=January 20202017-07-06 |boturl-status=InternetArchiveBotdead |fixaccess-attempteddate=yes2006-10-13 }}</ref> This compiler introduced the Lisp model of incremental compilation, in which compiled and interpreted functions can intermix freely.

The two variants of Lisp most significant in the development of Scheme were both developed at MIT: LISP 1.5<ref>{{cite book |url=https://archive.org/details/lisp15programmer00john |title=LISP 1.5 Programmer's Manual |publisher=[[MIT Press]] |lastlast1=McCarthy |firstfirst1=John |author-link=John McCarthy (computer scientist) |last2=Abrahams |first2=Paul W. |last3=Edwards |first3=Daniel J. |last4=Hart |first4=Timothy P. |last5=Levin |first5=Michael I. |isbn=978-0-262-13011-0 |year=1985 |url-access=registration }}</ref> developed by McCarthy and others, and [[Maclisp]]<ref>{{cite web |url=http://zane.brouhaha.com/~healyzh/doc/lisp.doc.txt |title=Maclisp Reference Manual |date=March 3, 1979 |archive-url=https://web.archive.org/web/20071214064433/http://zane.brouhaha.com/~healyzh/doc/lisp.doc.txt |archive-date=2007-12-14}}</ref> – developed for MIT's [[Project MAC]], a direct descendant of LISP 1.5. which ran on the PDP-10 and [[Multics]] systems.

Since its inception, Lisp was closely connected with the [[artificial intelligence]] (AI) research community, especially on [[PDP-10]]. The 36-bit word size of the [[PDP-6]] and [[PDP-10]] was influenced by the usefulness of having two Lisp [[18-bit computing|18-bit]] pointers in one word.<ref>{{cite newsgroup |quote=The PDP-6 project started in early 1963, as a [[24-bit computing|24-bit]] machine. It grew to 36 bits for LISP, a design goal. |url=https://groups.google.com/group/alt.folklore.computers/browse_thread/thread/6e5602ce733d0ec/17597705ae289112 |title=The History of TOPS or Life in the Fast ACs |newsgroup=alt.folklore.computers |message-id= [e-mail] |date=18 October 1990 |last=Hurley |first=Peter J.}}</ref>

===ALGOL===

{{detailsFurther|ALGOL}}

[[ALGOL 58]], originally to be called IAL for "International Algorithmic Language", was developed jointly by a committee of European and American computer scientists in a meeting in 1958 at [[ETH Zurich]]. [[ALGOL 60]], a later revision developed at the ALGOL 60 meeting in Paris and now commonly named [[ALGOL]], became the standard for the publication of algorithms and had a profound effect on future language development, despite the language's lack of commercial success and its limitations. [[Tony Hoare]] has remarked: "Here is a language so far ahead of its time that it was not only an improvement on its predecessors but also on nearly all its successors."<ref>{{cite book |last=Hoare |first=Tony |author-link=Tony Hoare |date=December 1973 |title=Hints on Programming Language Design |url=http://www.eecs.umich.edu/~bchandra/courses/papers/Hoare_Hints.pdf |page=27 }} (This statement is sometimes erroneously attributed to [[Edsger W. Dijkstra]], also involved in implementing the first ALGOL 60 [[compiler]].)</ref>

ALGOL introduced the use of block structure and lexical scope. It was also notorious for its difficult [[call by name]] default parameter passing mechanism, which was defined so as to require textual substitution of the expression representing the working parameter in place of the formal parameter during execution of a procedure or function, causing it to be re-evaluated each time it is referenced during execution. ALGOL implementors developed a mechanism they called a [[thunk]], which captured the context of the working parameter, enabling it to be evaluated during execution of the procedure or function.

==Carl Hewitt, the Actor model, and the birth of Scheme==

{{See also|Actor model|Planner (programming language)|MDL (programming language)}}

In 1971 Sussman, [[Drew McDermott]], and [[Eugene Charniak]] had developed a system called [[Planner (programming language)#Micro-planner implementation|Micro-Planner]] which was a partial and somewhat unsatisfactory implementation of [[Carl Hewitt]]'s ambitious [[Planner (programming language)|Planner]] project. Sussman and Hewitt worked together along with others on Muddle, later renamed [[MDL (programming language)|MDL]], an extended Lisp which formed a component of Hewitt's project. Drew McDermott, and Sussman in 1972 developed the Lisp-based language ''Conniver'', which revised the use of automatic backtracking in Planner which they thought was unproductive. Hewitt was dubious that the "hairy control structure" in Conniver was a solution to the problems with Planner. [[Pat Hayes]] remarked: "Their [Sussman and McDermott] solution, to give the user access to the implementation primitives of Planner, is however, something of a retrograde step (what are Conniver's semantics?)"<ref>{{cite journal |last=Hayes |first=Pat |date=1974 |title=Some Problems and Non-Problems in Representation Theory |journal=Society for the Study of Artificial Intelligence and the Simulation of Behaviour (AISB) }}</ref>

In November 1972, Hewitt and his students invented the [[Actor model]] of computation as a solution to the problems with Planner.<ref name="hewitt1973">{{cite journal |lastlast1=Hewitt |firstfirst1=Carl |author-link=Carl Hewitt |last2=Bishop |first2=Peter |last3=Steiger |first3=Richard |title=A Universal Modular Actor Formalism for Artificial Intelligence |publisher=IJCAI |year=1973}}</ref> A partial implementation of Actors was developed called Planner-73 (later called PLASMA). Steele, then a graduate student at MIT, had been following these developments, and he and Sussman decided to implement a version of the Actor model in their own "tiny Lisp" developed on [[Maclisp]], to understand the model better. Using this basis they then began to develop mechanisms for creating actors and sending messages.<ref name="revisited">{{cite journal

|lastlast1=Sussman |firstfirst1=Gerald Jay |author-link=Gerald Jay Sussman |last2=Steele Jr. |first2=Guy L. |author-link2=Guy L. Steele Jr.

|date = December 1998

|url = http://www.brics.dk/~hosc/local/HOSC-11-4-pp399-404.pdf

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|pages = 399–404

|doi = 10.1023/A:1010079421970

|s2cid=7704398 |issn = 1388-3690

|access-date = 2006-06-19

|url-status = dead

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}}</ref>

PLASMA's use of lexical scope was similar to the [[lambda calculus]]. Sussman and Steele decided to try to model Actors in the lambda calculus. They called their modeling system Schemer, eventually changing it to Scheme to fit the six-character limit on the [[Incompatible Timesharing System|ITS]] file system on their DEC [[PDP-10]]. They soon concluded Actors were essentially closures that never return but instead invoke a [[continuation]], and thus they decided that the closure and the Actor were, for the purposes of their investigation, essentially identical concepts. They eliminated what they regarded as redundant code and, at that point, discovered that they had written a very small and capable dialect of Lisp. Hewitt remained critical of the "hairy control structure" in Scheme<ref>{{cite journal |last=Hewitt |first=Carl |author-link=Carl Hewitt |date=December 1976 |title=Viewing Control Structures as Patterns of Passing Messages |journal=AI Memo 410 }}</ref><ref>{{cite journal |last=Hewitt |first=Carl |author-link=Carl Hewitt |date=June 1977 |title=Viewing Control Structures as Patterns of Passing Messages |journal=Journal of Artificial Intelligence |volume=8 |issue=3 |pages=323–364 |doi=10.1016/0004-3702(77)90033-9 |hdl=1721.1/6272 |hdl-access=free }}</ref> and considered primitives (e.g., <code>START!PROCESS</code>, <code>STOP!PROCESS</code>, and <code>EVALUATE!UNINTERRUPTIBLY</code>) used in the Scheme implementation to be a backward step.

25 years later, in 1998, Sussman and Steele reflected that 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 a powerful and expressive programming language."<ref name="revisited"/>

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==Influence==

Scheme was the first dialect of Lisp to choose [[Scope (computer science)|lexical scope]]. It was also one of the first programming languages after Reynold's Definitional Language<ref>{{cite conference |title=Definitional interpreters for higher order programming languages |last=Reynolds |first=John |date=1972 |book-title=ACM Conference Proceedings |conference=Association for Computing Machinery }}</ref> to support [[First-class citizen|first-class]] [[continuation]]s. It had a large impact on the effort that led to the development of its sister-language, [[Common Lisp]], to which Guy Steele was a contributor.<ref name="lispworks">{{cite web |url=http://www.lispworks.com/documentation/HyperSpec/Body/01_ab.htm |title=Common Lisp Hyperspec – 1.1.2 History |author=<!--Unstated.--> |date=2005 |website=LispWorks |access-date=2018-12-02}}</ref>

==Standardization==

The Scheme language is [[Technical standard|standardized]] in the official [[Institute of Electrical and Electronics Engineers]] (IEEE) standard,<ref name="ieee1178">1178-1990 (R1995) IEEE Standard for the Scheme Programming Language</ref> and a de facto standard called the ''Revisedⁿ Report on the Algorithmic Language Scheme'' (R''n''RS). The most widely implemented standard is ''R5RS'' (1998),<ref name="r5rs">{{cite journal

|lastlast1=Kelsey |firstfirst1=Richard |last2=Clinger |first2=William |last3=Rees |first3=Jonathan

|date=August 1998

|title=Revised⁵ Report on the Algorithmic Language Scheme

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|pages=7–105

|doi=10.1023/A:1010051815785

|display-authors=etal|url-access=subscription
}}</ref> and a new standard, ''R6RS'',<ref name="r6rs">{{cite journal

|lastlast1=Sperber |firstfirst1=Michael |last2=Dybvig |first2=R. Kent |last3=Flatt |first3=Matthew |last4=Van Straaten |first4=Anton |last5=Findler |first5=Robby |last6=Matthews |first6=Jacob

|date=August 2009

|title=Revised⁶ Report on the Algorithmic Language Scheme

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|pages=1–301

|doi=10.1017/S0956796809990074

|citeseerx=10.1.1.154.5197 |s2cid=62724224 }}</ref> was ratified in 2007.<ref>{{cite web |url=http://www.r6rs.org/ratification/results.html |title=R6RS ratification-voting results }}</ref> Besides the RnRS standards there are also [[Scheme Requests for Implementation]] documents, that contain additional libraries that may be added by Scheme implementations.

==Timeline==

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[[Category:History of software|Scheme programming language]]

[[Category:Scheme (programming language)]]

[[Category:Software topical history overviews|Scheme programming language]]