Lisp (programming language): Difference between revisions

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{{Infobox programming language

| name = Lisp

| logo = Lisp logo.svg

| logo size = 150px

| paradigm = [[Multi-paradigm programming language|Multi-paradigm]]: [[Functional programming|functional]], [[Procedural programming|procedural]], [[Reflective programming|reflective]], [[Metaprogramming|meta]]

| released = {{Start date and age|1960}}

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{{Multiple image |direction=vertical |image1=John McCarthy Stanford.jpg |image2=Steve Russell.jpg |footer=[[John McCarthy (computer scientist)|John McCarthy]] (top) and [[Steve Russell (computer scientist)|Steve Russell]]}}

[[John McCarthy (computer scientist)|John McCarthy]] began developing Lisp in 1958 while he was at the [[Massachusetts Institute of Technology]] (MIT). He was motivated by a desire to create an AI programming language that would work on the [[IBM 704]], as he believed that "IBM looked like a good bet to pursue Artificial Intelligence research vigorously."<ref name="wexelblat-history-programming-languages">{{cite book |title=History of programming languages |last1=McCarthy |first1=John |last2=Wexelblat |first2=Richard L. |year=1978 |isbn=0127450408 |publisher=Association for Computing Machinery |pages=173–183}}</ref> He was inspired by [[Information Processing Language]], which was also based on list processing, but did not use it because it was designed for different hardware and he found an algebraic language more appealing.<ref name="wexelblat-history-programming-languages" /> Due to these factors, he consulted on the design of the [[Fortran]] List Processing Language, which was implemented as a Fortran library. However, he was dissatisfied with it because it did not support [[Recursion (computer science)|recursion]] or a modern [[Conditional (computer programming)#If–then(–else)|if-then-else]] statement (which was a new concept when lispLisp was first introduced) {{NoteTag|At the time, Fortran had an if-then-else construct that accepted line numbers as jump targets, in the manner of a [[Goto]] statement, rather than accepting arbitrary expression in "then" and "else" blocks}}.<ref name="wexelblat-history-programming-languages" />

McCarthy's original notation used bracketed "[[M-expression]]s" that would be translated into [[S-expression]]s. As an example, the M-expression {{Lisp2|car[cons[A,B]]}} is equivalent to the S-expression {{Lisp2|(car (cons A B))}}. Once Lisp was implemented, programmers rapidly chose to use S-expressions, and M-expressions were abandoned.<ref name="wexelblat-history-programming-languages"/> M-expressions surfaced again with short-lived attempts of [[MLisp]]<ref name="Smith">{{cite book |last=Smith |first=David Canfield |title=MLISP Users Manual |url=http://www.softwarepreservation.org/projects/LISP/stanford/Smith-MLISP-AIM-84.pdf |access-date=2006-10-13}}</ref> by Horace Enea and [[CGOL]] by [[Vaughan Pratt]].

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[[Garbage collection (computer science)|Garbage collection]] routines were developed by MIT graduate student [[Daniel Edwards (programmer)|Daniel Edwards]], prior to 1962.<ref>{{cite book |title=LISP 1.5 Programmer's Manual |url=http://www.softwarepreservation.org/projects/LISP/book/LISP%201.5%20Programmers%20Manual.pdf |page=Preface |orig-date=1962 |year=1985 |version=15th printing |last1=McCarthy |first1=John |last2=Abrahams |first2=Paul W. |last3=Edwards |first3=Daniel J. |last4=Hart |first4=Timothy P. |last5=Levin |first5=Michael I. |edition=2nd}}</ref>

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 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".

=== Timeline ===

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===Conses and lists===

{{Main|Cons}}

[[File:Cons-cellsCell.svg|thumb|right|300px|Box-andCons-[[pointercell (computeras programming)|pointer]]an diagramomnipresent foriconographic thedepiction listin (42LISP 69 613)literature.]]

A Lisp list is implemented as a [[singly linked list]].<ref name="SebestaLanguages">{{cite book |last1=Sebesta |first1=Robert W. |title=Concepts of Programming Languages |chapter="2.4 Functional Programming: LISP";"6.9 List Types";"15.4 The First Functional Programming Language: LISP" |date=2012 |publisher=Addison-Wesley |___location=Boston, MA, US |isbn=978-0-13-139531-2 |pages=47–52;281–284;677–680 |edition=10th |url=https://www.pearson.com/us/higher-education/product/Sebesta-Concepts-of-Programming-Languages-10th-Edition/9780131395312.html |language=en |format=print}}</ref> Each cell of this list is called a ''cons'' (in Scheme, a ''pair'') and is composed of two [[pointer (computer programming)|pointers]], called the [[CAR and CDR|''car'' and ''cdr'']]. These are respectively equivalent to the {{Lisp2|data}} and {{Lisp2|next}} fields discussed in the article ''[[linked list]]''.

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====S-expressions represent lists====

[[File:Cons-cells.svg|thumb|right|300px|Box-and-[[pointer (computer programming)|pointer]] diagram for the list (42 69 613)]]

Parenthesized S-expressions represent linked list structures. There are several ways to represent the same list as an S-expression. A cons can be written in ''dotted-pair notation'' as {{Lisp2|(a . b)}}, where {{Lisp2|a}} is the car and {{Lisp2|b}} the cdr. A longer proper list might be written {{Lisp2|(a . (b . (c . (d . nil))))}} in dotted-pair notation. This is conventionally abbreviated as {{Lisp2|(a b c d)}} in ''list notation''. An improper list<ref name="r3sL3">NB: a so-called "dotted list" is only one kind of "improper list". The other kind is the "circular list" where the cons cells form a loop. Typically this is represented using #n=(...) to represent the target cons cell that will have multiple references, and #n# is used to refer to this cons. For instance, (#1=(a b) . #1#) would normally be printed as ((a b) a b) (without circular structure printing enabled), but makes the reuse of the cons cell clear. #1=(a . #1#) cannot normally be printed as it is circular, although (a...) is sometimes displayed, the CDR of the cons cell defined by #1= is itself.</ref> may be written in a combination of the two – as {{Lisp2|(a b c . d)}} for the list of three conses whose last cdr is {{Lisp2|d}} (i.e., the list {{Lisp2|(a . (b . (c . d)))}} in fully specified form).