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69-704: TOPS-20 began in 1969 as the TENEX operating system of Bolt, Beranek and Newman (BBN) and shipped as a product by DEC starting in 1976. TOPS-20 is almost entirely unrelated to the similarly named TOPS-10 , but it was shipped with the PA1050 TOPS-10 Monitor Calls emulation facility which allowed most, but not all, TOPS-10 executables to run unchanged. As a matter of policy, DEC did not update PA1050 to support later TOPS-10 additions except where required by DEC software. TOPS-20 competed with TOPS-10, ITS and WAITS —all of which were notable time-sharing systems for

138-422: A Model B hardware revision to enlarge the user virtual address space. Some effective address calculations by instructions located beyond the original 18-bit address space were performed to 30 significant bits, although only a 23-bit virtual address space was supported. Program code located in the original 18-bit address space had unchanged semantics, for backward compatibility . The first in-house code name for

207-754: A GTJFN (Get Job File Number) JSYS, and then that JFN number was used to open (OPENF) and manipulate the file's contents. PCL (Programmable Command Language) is a programming language that runs under TOPS-20. PCL source programs are, by default, stored with Filetype .PCL, and enable extending the TOPS-20 EXEC via a verb named DECLARE. Newly compiled commands then become functionally part of the EXEC. PCL includes: Paul Allen maintained several publicly accessible historic computer systems before his death, including an XKL TOAD-2 running TOPS-20. See also SDF Public Access Unix System . TENEX (operating system) TENEX

276-526: A decade earlier than Common Lisp, Scheme is a more minimalist design. It has a much smaller set of standard features but with certain implementation features (such as tail-call optimization and full continuations ) not specified in Common Lisp. A wide variety of programming paradigms, including imperative, functional, and message passing styles, find convenient expression in Scheme. Scheme continues to evolve with

345-407: A flexible and powerful form of dynamic dispatch . It has served as the template for many subsequent Lisp (including Scheme ) object systems, which are often implemented via a metaobject protocol , a reflective meta-circular design in which the object system is defined in terms of itself: Lisp was only the second language after Smalltalk (and is still one of the very few languages) to possess such

414-617: A great compliment because it transmits the full flavour of liberation: it has assisted a number of our most gifted fellow humans in thinking previously impossible thoughts. Largely because of its resource requirements with respect to early computing hardware (including early microprocessors), Lisp did not become as popular outside of the AI community as Fortran and the ALGOL -descended C language. Because of its suitability to complex and dynamic applications, Lisp enjoyed some resurgence of popular interest in

483-460: A language others considered antiquated. New Lisp programmers often describe the language as an eye-opening experience and claim to be substantially more productive than in other languages. This increase in awareness may be contrasted to the " AI winter " and Lisp's brief gain in the mid-1990s. As of 2010 , there were eleven actively maintained Common Lisp implementations. The open source community has created new supporting infrastructure: CLiki

552-431: A list of files in a directory, whereas TENEX used DIRECTORY (OF FILES) . " DIRECTORY " was the command word, " (OF FILES) " was noise added to make the purpose of the command clearer. To relieve users of the need to type these long commands, TENEX used a command completion system that understood unambiguously abbreviated command words, and expanded partial command words into complete words or phrases. For instance,

621-590: A low-cost version of the KI-10. While this was going on, Stanford University AI programmers, many of them MIT alumni , were working on their own project to build a PDP-10 that was ten times faster than the original KA-10. The project evolved into the Foonly line of computers. DEC visited them and many of their ideas were then folded into the KL-10 project. The same year IBM also announced their own machine with virtual memory, making it

690-445: A metaobject system. Many years later, Alan Kay suggested that as a result of the confluence of these features, only Smalltalk and Lisp could be regarded as properly conceived object-oriented programming systems. Lisp introduced the concept of automatic garbage collection , in which the system walks the heap looking for unused memory. Progress in modern sophisticated garbage collection algorithms such as generational garbage collection

759-490: A much simpler single-level page mapping system. This compromise impacted system sales; by this point TENEX was the most popular customer-written PDP-10 operating systems, but it would not run on the new, faster KI-10s. To correct this problem, the DEC PDP-10 sales manager purchased the rights to TENEX from BBN and set up a project to port it to the new machine. At around this time Murphy moved from BBN to DEC as well, helping on

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828-578: A paper in Communications of the ACM in April 1960, entitled "Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I". He showed that with a few simple operators and a notation for anonymous functions borrowed from Church, one can build a Turing-complete language for algorithms. Information Processing Language was the first AI language, from 1955 or 1956, and already included many of

897-728: A series of standards (Revised Report on the Algorithmic Language Scheme) and a series of Scheme Requests for Implementation . Clojure is a dialect of Lisp that targets mainly the Java virtual machine , and the Common Language Runtime (CLR), the Python VM, the Ruby VM YARV , and compiling to JavaScript . It is designed to be a pragmatic general-purpose language. Clojure draws considerable influences from Haskell and places

966-510: A single language. The new language, Common Lisp , was somewhat compatible with the dialects it replaced (the book Common Lisp the Language notes the compatibility of various constructs). In 1994, ANSI published the Common Lisp standard, "ANSI X3.226-1994 Information Technology Programming Language Common Lisp". Since inception, Lisp was closely connected with the artificial intelligence research community, especially on PDP-10 systems. Lisp

1035-437: A standard data structure—a quality much later dubbed " homoiconicity ". Thus, Lisp functions can be manipulated, altered or even created within a Lisp program without lower-level manipulations. This is generally considered one of the main advantages of the language with regard to its expressive power, and makes the language suitable for syntactic macros and meta-circular evaluation . A conditional using an if–then–else syntax

1104-477: A standard requirement for any computer. In the end the KL integrated a number of major changes to the system, but did not end up being any lower in cost. From the start, the new DECSYSTEM-20 would run a version of TENEX as its default operating system. Functional upgrades for the KL-10 processor architecture were limited. The most significant new feature (called extended addressing ) was modified pager microcode running on

1173-427: A very strong emphasis on immutability. Clojure provides access to Java frameworks and libraries, with optional type hints and type inference , so that calls to Java can avoid reflection and enable fast primitive operations. Clojure is not designed to be backwards compatible with other Lisp dialects. Further, Lisp dialects are used as scripting languages in many applications, with the best-known being Emacs Lisp in

1242-808: Is a weekly news service, Weekly Lisp News . Common-lisp.net is a hosting site for open source Common Lisp projects. Quicklisp is a library manager for Common Lisp. Fifty years of Lisp (1958–2008) was celebrated at LISP50@OOPSLA. There are regular local user meetings in Boston, Vancouver, and Hamburg. Other events include the European Common Lisp Meeting, the European Lisp Symposium and an International Lisp Conference. The Scheme community actively maintains over twenty implementations . Several significant new implementations (Chicken, Gambit, Gauche, Ikarus, Larceny, Ypsilon) have been developed in

1311-520: Is a wiki that collects Common Lisp related information, the Common Lisp directory lists resources, #lisp is a popular IRC channel and allows the sharing and commenting of code snippets (with support by lisppaste , an IRC bot written in Lisp), Planet Lisp collects the contents of various Lisp-related blogs, on LispForum users discuss Lisp topics, Lispjobs is a service for announcing job offers and there

1380-450: Is an operating system developed in 1969 by BBN for the PDP-10 , which later formed the basis for Digital Equipment Corporation 's TOPS-20 operating system. In the 1960s, BBN was involved in a number of LISP -based artificial intelligence projects for DARPA , many of which had very large (for the era) memory requirements. One solution to this problem was to add paging software to

1449-565: Is implemented in Femtolisp, a dialect of Scheme (Julia is inspired by Scheme, which in turn is a Lisp dialect). In October 2019, Paul Graham released a specification for Bel , "a new dialect of Lisp." Common Lisp and Scheme represent two major streams of Lisp development. These languages embody significantly different design choices. Common Lisp is a successor to Maclisp . The primary influences were Lisp Machine Lisp , Maclisp, NIL , S-1 Lisp , Spice Lisp , and Scheme. It has many of

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1518-480: Is intended for reading, not for computing. But he went ahead and did it. That is, he compiled the eval in my paper into IBM 704 machine code, fixing bugs , and then advertised this as a Lisp interpreter, which it certainly was. So at that point Lisp had essentially the form that it has today ... The result was a working Lisp interpreter which could be used to run Lisp programs, or more properly, "evaluate Lisp expressions". Two assembly language macros for

1587-507: Is written as s-expressions , or parenthesized lists. A function call or syntactic form is written as a list with the function or operator's name first, and the arguments following; for instance, a function f that takes three arguments would be called as ( f arg1 arg2 arg3 ) . John McCarthy began developing Lisp in 1958 while he was at the Massachusetts Institute of Technology (MIT). McCarthy published its design in

1656-406: Is written with its elements separated by whitespace , and surrounded by parentheses. For example, ( 1 2 foo ) is a list whose elements are the three atoms 1 , 2 , and foo . These values are implicitly typed: they are respectively two integers and a Lisp-specific data type called a "symbol", and do not have to be declared as such. The empty list () is also represented as

1725-686: The Emacs editor, AutoLISP and later Visual Lisp in AutoCAD , Nyquist in Audacity , and Scheme in LilyPond . The potential small size of a useful Scheme interpreter makes it particularly popular for embedded scripting. Examples include SIOD and TinyScheme , both of which have been successfully embedded in the GIMP image processor under the generic name "Script-fu". LIBREP, a Lisp interpreter by John Harper originally based on

1794-536: The Emacs Lisp language, has been embedded in the Sawfish window manager . Lisp has officially standardized dialects: R6RS Scheme , R7RS Scheme , IEEE Scheme, ANSI Common Lisp and ISO ISLISP . Paul Graham identifies nine important aspects of Lisp that distinguished it from existing languages like Fortran : Lisp was the first language where the structure of program code is represented faithfully and directly in

1863-554: The IBM 704 became the primitive operations for decomposing lists: car ( Contents of the Address part of Register number) and cdr ( Contents of the Decrement part of Register number), where "register" refers to registers of the computer's central processing unit (CPU). Lisp dialects still use car and cdr ( / k ɑːr / and / ˈ k ʊ d ər / ) for the operations that return

1932-526: The LISP language, allowing it to write out unused portions of memory to disk for later recall if needed. One such system had been developed for the PDP-1 at MIT by Daniel Murphy before he joined BBN. Early DEC machines were based on an 18-bit word, allowing addresses to encode for a 256 kiloword memory. The machines were based on expensive core memory and included nowhere near the required amount. The pager used

2001-590: The LLVM , the Java virtual machine , x86-64, PowerPC, Alpha, ARM, Motorola 68000, and MIPS, and operating systems such as Windows, macOS, Linux, Solaris, FreeBSD, NetBSD, OpenBSD, Dragonfly BSD, and Heroku. Scheme is a statically scoped and properly tail-recursive dialect of the Lisp programming language invented by Guy L. Steele, Jr. and Gerald Jay Sussman . It was designed to have exceptionally clear and simple semantics and few different ways to form expressions. Designed about

2070-457: The PDP-10 during this timeframe. TOPS-20 is informally known as TWENEX. TOPS-20 was based upon the TENEX operating system, which had been created by Bolt Beranek and Newman for Digital's PDP-10 computer. After Digital started development of the KI-10 version of the PDP-10, an issue arose: by this point TENEX was the most popular customer-written PDP-10 operating systems, but it would not run on

2139-456: The PDP-10 . BBN started talks with DEC to get a paging subsystem in the new machine, then known by its CPU name, the KA-10. DEC was not interested; however, one development of these talks was support in the PDP-10 for a second virtual memory segment, allowing half of the user address space to be mapped to a separate (potentially read-only) region of physical memory. Additionally, DEC insisted on keeping

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2208-482: The read–eval–print loop . The name LISP derives from "LISt Processor". Linked lists are one of Lisp's major data structures , and Lisp source code is made of lists. Thus, Lisp programs can manipulate source code as a data structure, giving rise to the macro systems that allow programmers to create new syntax or new domain-specific languages embedded in Lisp. The interchangeability of code and data gives Lisp its instantly recognizable syntax. All program code

2277-473: The 2000s (decade). The Revised Report on the Algorithmic Language Scheme standard of Scheme was widely accepted in the Scheme community. The Scheme Requests for Implementation process has created a lot of quasi-standard libraries and extensions for Scheme. User communities of individual Scheme implementations continue to grow. A new language standardization process was started in 2003 and led to

2346-482: The 2010s. Lisp is an expression oriented language . Unlike most other languages, no distinction is made between "expressions" and "statements" ; all code and data are written as expressions. When an expression is evaluated , it produces a value (possibly multiple values), which can then be embedded into other expressions. Each value can be any data type. McCarthy's 1958 paper introduced two types of syntax: Symbolic expressions ( S-expressions , sexps), which mirror

2415-491: The Extensible Markup Language ( XML ). The reliance on expressions gives the language great flexibility. Because Lisp functions are written as lists, they can be processed exactly like data. This allows easy writing of programs which manipulate other programs ( metaprogramming ). Many Lisp dialects exploit this feature using macro systems, which enables extension of the language almost without limit. A Lisp list

2484-556: The Lisp model of incremental compilation , in which compiled and interpreted functions can intermix freely. The language used in Hart and Levin's memo is much closer to modern Lisp style than McCarthy's earlier code. Garbage collection routines were developed by MIT graduate student Daniel Edwards , prior to 1962. During the 1980s and 1990s, a great effort was made to unify the work on new Lisp dialects (mostly successors to Maclisp such as ZetaLisp and NIL (New Implementation of Lisp) into

2553-470: The R RS Scheme standard in 2007. Academic use of Scheme for teaching computer science seems to have declined somewhat. Some universities are no longer using Scheme in their computer science introductory courses; MIT now uses Python instead of Scheme for its undergraduate computer science program and MITx massive open online course. There are several new dialects of Lisp: Arc , Hy , Nu , Liskell , and LFE (Lisp Flavored Erlang). The parser for Julia

2622-456: The S-expression syntax is also responsible for much of Lisp's power: the syntax is simple and consistent, which facilitates manipulation by computer. However, the syntax of Lisp is not limited to traditional parentheses notation. It can be extended to include alternative notations. For example, XMLisp is a Common Lisp extension that employs the metaobject protocol to integrate S-expressions with

2691-503: The TOPS-20 Command Processor. JSYS stands for J ump to SYS tem. Operands were at times memory addresses. "TOPS-20 allows you to use 18-bit or 30-bit addresses. Some monitor calls require one kind, some the other; some calls accept either kind. Some monitor calls use only 18 bits to hold an address. These calls interpret 18-bit addresses as locations in the current section." Internally, files were first identified, using

2760-596: The concepts, such as list-processing and recursion, which came to be used in Lisp. McCarthy's original notation used bracketed " M-expressions " that would be translated into S-expressions . As an example, the M-expression car[cons[A,B]] is equivalent to the S-expression ( car ( cons A B )) . Once Lisp was implemented, programmers rapidly chose to use S-expressions, and M-expressions were abandoned. M-expressions surfaced again with short-lived attempts of MLisp by Horace Enea and CGOL by Vaughan Pratt . Lisp

2829-418: The core theme of an S-expression language. Moreover, each given dialect may have several implementations—for instance, there are more than a dozen implementations of Common Lisp . Differences between dialects may be quite visible—for instance, Common Lisp uses the keyword defun to name a function, but Scheme uses define . Within a dialect that is standardized, however, conforming implementations support

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2898-419: The cost of the machine as low as possible, such as supporting systems with a minimum of 16K words of core, and omitting the fast semiconductor register option (substituting core), at the cost of a considerable performance decrease. BBN nevertheless went ahead with its purchase of several PDP-10s, and decided to build their own hardware pager. During this period a debate began on what operating system to run on

2967-596: The features of Lisp Machine Lisp (a large Lisp dialect used to program Lisp Machines ), but was designed to be efficiently implementable on any personal computer or workstation. Common Lisp is a general-purpose programming language and thus has a large language standard including many built-in data types, functions, macros and other language elements, and an object system ( Common Lisp Object System ). Common Lisp also borrowed certain features from Scheme such as lexical scoping and lexical closures . Common Lisp implementations are available for targeting different platforms such as

3036-415: The first item in a list and the rest of the list, respectively. The first complete Lisp compiler, written in Lisp, was implemented in 1962 by Tim Hart and Mike Levin at MIT, and could be compiled by simply having an existing LISP interpreter interpret the compiler code, producing machine code output able to be executed at a 40-fold improvement in speed over that of the interpreter. This compiler introduced

3105-504: The internal representation of code and data; and Meta expressions ( M-expressions ), which express functions of S-expressions. M-expressions never found favor, and almost all Lisps today use S-expressions to manipulate both code and data. The use of parentheses is Lisp's most immediately obvious difference from other programming language families. As a result, students have long given Lisp nicknames such as Lost In Stupid Parentheses , or Lots of Irritating Superfluous Parentheses . However,

3174-457: The late 1950s, it is the second-oldest high-level programming language still in common use, after Fortran . Lisp has changed since its early days, and many dialects have existed over its history. Today, the best-known general-purpose Lisp dialects are Common Lisp , Scheme , Racket , and Clojure . Lisp was originally created as a practical mathematical notation for computer programs , influenced by (though not originally derived from)

3243-557: The late 1980s, most of the TOPS-20 users had migrated to Unix. A loyal group of TOPS-20 enthusiasts kept working on various projects to preserve and extend TOPS-20, notably Mark Crispin and the Panda TOPS-20 distribution. LISP Lisp (historically LISP , an abbreviation of "list processing") is a family of programming languages with a long history and a distinctive, fully parenthesized prefix notation . Originally specified in

3312-512: The most significant bits of the address to index a table of blocks on a magnetic drum that acted as the pager's backing store . The software would fetch the pages if needed, and then resolve the address to the proper area of RAM . In 1964 DEC announced the PDP-6 . DEC was still heavily involved with MIT's AI Lab, and many feature requests from the LISP hackers were moved into this machine. 36-bit computing

3381-488: The name TENEX (TEN-EXtended) for the new system. It included a full virtual memory system—that is, not only could programs access a full 18 bit address space of 262144 words of virtual memory, every program could do so at the same time. The pager system would handle mapping as it would always, copying data to and from the backing store as needed. The only change needed was for the pager to be able to hold several sets of mappings between RAM and store, one for each program using

3450-573: The new machines. Strong arguments were made for the continued use of TOPS-10, in order to keep their existing software running with minimum effort. This would require a re-write of TOPS-10 to support the paging system, and this seemed like a major problem. At the same time, TOPS-10 did not support a number of features the developers wanted. In the end they decided to make a new system, but include an emulation library that would allow it to run existing TOPS-10 software with minor effort. The developer team—amongst them Daniel Murphy and Daniel G. Bobrow —chose

3519-676: The new, faster KI-10s. To correct this problem, the DEC PDP-10 sales manager purchased the rights to TENEX from BBN and set up a project to port it to the new machine. In the end, very little of the original TENEX code remained, and Digital ultimately named the resulting operating system TOPS-20. Some of what came with TOPS-20 was merely an emulation of the TOPS-10 Operating System's calls. These were known as UUO's, standing for Unimplemented User Operation, and were needed both for compilers, which were not 20-specific, to run, as well as user-programs written in these languages. The package that

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3588-415: The notation of Alonzo Church 's lambda calculus . It quickly became a favored programming language for artificial intelligence (AI) research. As one of the earliest programming languages, Lisp pioneered many ideas in computer science , including tree data structures , automatic storage management , dynamic typing , conditionals , higher-order functions , recursion , the self-hosting compiler , and

3657-488: The operating system was VIROS (VIRtual memory Operating System); when customers started asking questions, the name was changed to SNARK so that DEC could truthfully deny that there was any project called VIROS. When the name SNARK became known, the name was briefly reversed to become KRANS; this was quickly abandoned when someone objected that " krans " meant "funeral wreath" in Swedish (though it simply means "wreath"; this part of

3726-518: The porting project. Most of the work centered on emulating the BBN pager hardware in a combination of software and the KI-10's simpler hardware. The speed of the KI-10 compared to the PDP-6 made this possible. Additionally the porting effort required a number of new device drivers to support the newer backing store devices being used. Just as the new TENEX was shipping, DEC started work on the KL-10, intended to be

3795-474: The same core language, but with different extensions and libraries. After having declined somewhat in the 1990s, Lisp has experienced a resurgence of interest after 2000. Most new activity has been focused around implementations of Common Lisp , Scheme , Emacs Lisp , Clojure , and Racket , and includes development of new portable libraries and applications. Many new Lisp programmers were inspired by writers such as Paul Graham and Eric S. Raymond to pursue

3864-406: The special atom nil . This is the only entity in Lisp which is both an atom and a list. Expressions are written as lists, using prefix notation . The first element in the list is the name of a function, the name of a macro, a lambda expression or the name of a "special operator" (see below). The remainder of the list are the arguments. For example, the function list returns its arguments as

3933-446: The story may be apocryphal). Ultimately DEC picked TOPS-20 as the name of the operating system, and it was as TOPS-20 that it was marketed. The hacker community , mindful of its origins, quickly dubbed it TWENEX (a portmanteau of "twenty TENEX"), even though by this point very little of the original TENEX code remained (analogously to the differences between AT&T V7 Unix and BSD ). DEC people cringed when they heard "TWENEX", but

4002-437: The system would have paging support invisibly, making programming much easier. DEC was initially interested, however in 1966 they announced they would be discontinuing the PDP-6 and concentrating solely on their smaller 18-bit and new 16-bit lines. The PDP-6 was expensive and complex, and therefore had not sold well. It was not long until it became clear that DEC was once again entering the 36-bit business with what would become

4071-461: The system. The pager also held access time information in order to tune performance. The resulting pager was fairly complex, filling a full-height 19" rackmount chassis. One notable feature of TENEX was its user-oriented command line interpreter . Unlike typical systems of the era, TENEX deliberately used long command names and even included non-significant noise words to further expand the commands for clarity. For instance, Unix uses ls to print

4140-591: The term caught on nevertheless (the written abbreviation "20x" was also used). TWENEX was successful and very popular; in fact, there was a period in the early 1980s when it commanded as fervent a culture of partisans as Unix or ITS —but DEC's decision to scrap all the internal rivals to the VAX architecture and its VMS operating system killed the DEC-20 and put an end to TWENEX's brief period of popularity. DEC attempted to convince TOPS-20 users to convert to VMS, but instead, by

4209-451: The user could type DIR and the escape key, at which point TENEX would replace DIR with the full command. The completion feature also worked with file names, which took some effort on the part of the interpreter, and the system allowed for long file names with human-readable descriptions. TENEX also included a command recognition help system: typing a question mark ( ? ), printed out a list of possible matching commands and then return

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4278-466: The user to the command line with the question mark removed. The command line completion and help live on in current CLIs like tcsh . TENEX became fairly popular in the small PDP-10 market, and the external pager hardware developed into a small business of its own. In early 1970 DEC started work on an upgrade to the PDP-10 processor, the KI-10. BBN once again attempted to get DEC to support a complex pager with indirect page tables, but instead DEC decided on

4347-409: Was especially useful for LISP programming because with an 18-bit address space, a word of storage on these systems contained two addresses, a perfect match for the common LISP CAR and CDR operations. BBN became interested in buying one for their AI work when they became available, but wanted DEC to add a hardware version of Murphy's pager directly into the system. With such an addition, every program on

4416-404: Was first implemented by Steve Russell on an IBM 704 computer using punched cards . Russell had read McCarthy's paper and realized (to McCarthy's surprise) that the Lisp eval function could be implemented in machine code . According to McCarthy Steve Russell said, look, why don't I program this eval  ... and I said to him, ho, ho, you're confusing theory with practice, this eval

4485-420: Was influenced by Smalltalk, with later dialects adopting object-oriented programming features (inheritance classes, encapsulating instances, message passing, etc.) in the 1970s. The Flavors object system introduced the concept of multiple inheritance and the mixin . The Common Lisp Object System provides multiple inheritance, multimethods with multiple dispatch , and first-class generic functions , yielding

4554-502: Was invented by McCarthy for a chess program written in Fortran . He proposed its inclusion in ALGOL , but it was not made part of the Algol 58 specification. For Lisp, McCarthy used the more general cond -structure. Algol 60 took up if–then–else and popularized it. Lisp deeply influenced Alan Kay , the leader of the research team that developed Smalltalk at Xerox PARC ; and in turn Lisp

4623-848: Was mapped into a user's address space was named PA1050: PA as in PAT as in compatibility; 10 as in DEC or PDP 10; 50 as in a PDP 10 Model 50, 10/50, 1050. Sometimes PA1050 was referred to as PAT, a name that was a good fit to the fact that PA1050, "was simply unprivileged user-mode code" that "performed the requested action, using JSYS calls where necessary." The major ways to get at TOPS-20 capabilities, and what made TOPS-20 important, were The "EXEC" accomplished its work primarily using Rather advanced for its day were some TOPS-20-specific features: One could then type ? to find out what operands were permitted/required. Pressing Ctrl-T displays status information . The following list of commands are supported by

4692-433: Was stimulated by its use in Lisp. Edsger W. Dijkstra in his 1972 Turing Award lecture said, With a few very basic principles at its foundation, it [LISP] has shown a remarkable stability. Besides that, LISP has been the carrier for a considerable number of in a sense our most sophisticated computer applications. LISP has jokingly been described as "the most intelligent way to misuse a computer". I think that description

4761-454: Was used as the implementation of the language Micro Planner , which was used in the famous AI system SHRDLU . In the 1970s, as AI research spawned commercial offshoots, the performance of existing Lisp systems became a growing issue, as programmers needed to be familiar with the performance ramifications of the various techniques and choices involved in the implementation of Lisp. Over its sixty-year history, Lisp has spawned many variations on

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