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{{Short description|Text-string-oriented programming language}} {{About|the programming language|the cleaning product|SnoBol (cleaner)}} {{Infobox programming language | name = SNOBOL | paradigm = [[imperative programming|Imperative]], [[Procedural programming|procedural]], [[unstructured programming|unstructured]] | year = {{Start date and age|1962}} | designer = [[David J. Farber]], [[Ralph Griswold]] and [[Ivan P. Polonsky]] | developer = David J. Farber, Ralph E. Griswold, Ivan P. Polonsky, and [[Bell Labs]] | latest release version = SNOBOL4 | latest release date = {{Start date and age|1967}} | implementations = SNOBOL, [[SPITBOL]] | influenced by = [[COMIT]] | influenced = [[AWK]], SL5, [[Icon (programming language)|Icon]], [[bs (programming language)|bs]], [[Lua (programming language)|Lua]]<ref>{{Citation |last1=Ierusalimschy |first1=Roberto |last2=de Figueiredo |first2=Luiz Henrique |last3=Celes |first3=Waldemar |title=Proceedings of the third ACM SIGPLAN conference on History of programming languages |chapter=The evolution of Lua | date=2007 |url=https://www.lua.org/doc/hopl.pdf |volume= |issue= |pages=26 |doi=10.1145/1238844.1238846 |isbn=9781595937667 |s2cid=475143 |access-date=}}</ref> | website = https://www.regressive.org/snobol4/ }} '''SNOBOL''' ("StriNg Oriented and symBOlic Language") is a series of [[programming language]]s developed between 1962 and 1967 at [[AT&T Corporation|AT&T]] [[Bell Laboratories]] by [[David J. Farber]], [[Ralph Griswold]] and Ivan P. Polonsky, culminating in SNOBOL4. It was one of a number of [[String (computer science)|text-string]]-oriented languages developed during the 1950s and 1960s; others included [[COMIT]] and [[TRAC (programming language)|TRAC]]. Despite the similar name, it is entirely unlike [[COBOL]]. SNOBOL4 stands apart from most programming languages of its era by having patterns as a [[first-class object|first-class data type]], a data type whose values can be manipulated in all ways permitted to any other data type in the programming language, and by providing operators for pattern [[concatenation]] and [[alternation (formal language theory)|alternation]]. SNOBOL4 patterns are a type of object and admit various manipulations, much like later [[object-oriented language]]s such as [[JavaScript]] whose patterns are known as [[regular expression]]s. In addition SNOBOL4 strings generated during execution can be treated as programs and either interpreted or compiled and executed (as in the [[eval]] function of other languages). SNOBOL4 was quite widely taught in larger U.S. universities in the late 1960s and early 1970s and was widely used in the 1970s and 1980s as a text manipulation language in the [[humanities]]. In the 1980s and 1990s, its use faded as newer languages such as [[AWK]] and [[Perl]] made string manipulation by means of [[regular expression]]s fashionable. SNOBOL4 patterns include a way to express [[Backus–Naur Form|BNF]] grammars, which are equivalent to [[context-free grammar]]s and more powerful than regular expressions.<ref>{{cite journal |author=Gimpel, J. F. |title=A theory of discrete patterns and their implementation in SNOBOL4 |journal=Communications of the ACM |volume=16 |issue=2 |date=February 1973 |pages=91–100 |doi=10.1145/361952.361960|s2cid=17059429 |doi-access=free }}</ref> The "regular expressions" in current versions of AWK and Perl are in fact extensions of regular expressions in the [[Regular language|traditional sense]], but regular expressions, unlike SNOBOL4 patterns, are not recursive, which gives a distinct computational advantage to SNOBOL4 patterns.<ref>{{cite web|url=http://www.drdobbs.com/architecture-and-design/programs-that-transform-their-own-source/228701469 |title=Dr. Dobb's: Programs That Transform Their Own Source Code; or: the Snobol Foot Joke |publisher=Dobbscodetalk.com |access-date=2011-12-04}}</ref> (Recursive expressions did appear in [[Perl 5 version history|Perl 5.10]], though, released in December 2007.<ref>{{cite web|author=Contact details |url=http://perldoc.perl.org/5.10.0/perlre.html#Extended-Patterns |title=perlre |publisher=perldoc.perl.org |access-date=2011-12-04}}</ref><ref>{{cite web|url=http://www.rexegg.com/regex-recursion.html|title=Recursive Regex Tutorial|access-date=2017-03-19}}</ref>) The later SL5 (1977)<ref>{{cite journal |first1=Ralph E. |last1=Griswold |first2=David R. |last2=Hanson |title=An Overview of SL5 |journal=ACM SIGPLAN Notices |volume=12 |issue=4 |pages=40–50 |date=April 1977 |doi=10.1145/954654.954658 |s2cid=38692673 |url=|doi-access=free }}</ref> and [[Icon (programming language)|Icon]] (1978) languages were designed by Griswold to combine the backtracking of SNOBOL4 pattern matching with more standard [[ALGOL]]-like structuring. == Development == === SNOBOL1 === The initial SNOBOL language was created as a tool to be used by its authors to work with the symbolic manipulation of polynomials. It was written in assembly language for the [[IBM 7090]]. It had a simple syntax, only one datatype, the string, no functions, and no declarations and very little error control. However, despite its simplicity and its "personal" nature its use began to spread to other groups. As a result, the authors decided to extend it and tidy it up. === SNOBOL2 === SNOBOL2 did exist but it was a short-lived intermediate development version without user-defined functions and was never released. === SNOBOL3 === SNOBOL was rewritten to add functions, both standard and user-defined, and the result was released as SNOBOL3. SNOBOL3 became quite popular and was rewritten for other computers than the IBM 7090 by other programmers. As a result, several incompatible dialects arose. === SNOBOL4 === As SNOBOL3 became more popular, the authors received more and more requests for extensions to the language. They also began to receive complaints about incompatibility and bugs in versions that they hadn't written. To address this and to take advantage of the new computers being introduced in the late 1960s, the decision was taken to develop SNOBOL4 with many extra datatypes and features but based on a [[virtual machine]] to allow improved portability across computers.<ref>See Chapter 1 of ''The Macro Implementation of SNOBOL4''</ref> The SNOBOL4 language translator was still written in assembly language. However the macro features of the assembler were used to define the virtual machine instructions of the '''S'''NOBOL '''I'''mplementation '''L'''anguage, the SIL. This very much improved the portability of the language by making it relatively easy to port the virtual machine which hosted the translator by recreating its virtual instructions on any machine which included a macro assembler or indeed a high level language.<ref>SNOBOL4 has been implemented using C to recreate the virtual machine instructions.</ref> The machine-independent language SIL arose as a generalization of string manipulation macros by [[Douglas McIlroy]], which were used extensively in the initial SNOBOL implementation. In 1969, McIlroy influenced the language again by insisting on addition of the table type to SNOBOL4.<ref name="Gris78">{{cite journal |last=Griswold |first=Ralph |author-link=Ralph Griswold |title=A history of the SNOBOL programming languages |journal=ACM SIGPLAN Notices |pages=275–308 |volume=13 |number=8 |year=1978 |doi=10.1145/960118.808393 |s2cid=5413577 |url=http://pdfs.semanticscholar.org/a404/c09b14e2b03496604387f532fd33975179ec.pdf |archive-url=https://web.archive.org/web/20190302233559/http://pdfs.semanticscholar.org/a404/c09b14e2b03496604387f532fd33975179ec.pdf |url-status=dead |archive-date=2019-03-02 }}</ref><ref>{{cite book |editor-link=Richard Wexelblat|editor-first=Richard L. |editor-last=Wexelblat |title=History of Programming Languages |orig-year=1981 |year=2014 |publisher=Academic Press |isbn=9781483266169 |pages=784}}</ref> == SNOBOL4 features == {{Original research|date=August 2020}} SNOBOL is distinctive in format and programming style, which are radically different from contemporary procedural languages such as [[Fortran]] and [[ALGOL]]. SNOBOL4 supports a number of built-in [[data type]]s, such as [[integer]]s and limited precision [[real number]]s, [[string (computer science)|strings]], [[pattern matching|pattern]]s, [[Array data type|array]]s, and [[associative array|table]]s (associative arrays), and also allows the programmer to define additional data types and new [[function (programming)|function]]s. SNOBOL4's programmer-defined data type facility was advanced at the time—it is similar to the records of the earlier [[COBOL]] and the later [[Pascal programming language|Pascal]] programming languages. All SNOBOL command lines are of the form :''label subject pattern'' '''=''' ''object'' ''':''' ''transfer'' Each of the five elements is optional. In general, the ''subject'' is matched against the ''pattern''. If the ''object'' is present, any matched portion is replaced by the ''object'' via rules for replacement. The ''transfer'' can be an absolute branch or a conditional branch dependent upon the success or failure of the subject evaluation, the pattern evaluation, the pattern match, the object evaluation or the final assignment. It can also be a transfer to code created and compiled by the program itself during a run. A SNOBOL pattern can be very simple or extremely complex. A simple pattern is just a text string (e.g. "ABCD"), but a complex pattern may be a large structure describing, for example, the complete grammar of a computer language. It is possible to implement a language interpreter in SNOBOL almost directly from a [[Backus–Naur form]] expression of it, with few changes. Creating a macro assembler and an interpreter for a completely theoretical piece of hardware could take as little as a few hundred lines, with a new instruction being added with a single line. Complex SNOBOL patterns can do things that would be impractical or impossible using the more primitive regular expressions used in most other pattern-matching languages. Some of this power derives from the so-called "SPITBOL extensions" (which have since been incorporated in basically all modern implementations of the original SNOBOL 4 language too), although it is possible to achieve the same power without them. Part of this power comes from the side effects that it is possible to produce during the pattern matching operation, including saving numerous intermediate/tentative matching results and the ability to invoke user-written functions during the pattern match which can perform nearly any desired processing, and then influence the ongoing direction the interrupted pattern match takes, or even to indeed change the pattern itself during the matching operation. Patterns can be saved like any other first-class data item, and can be concatenated, used within other patterns, and used to create very complex and sophisticated pattern expressions. It is possible to write, for example, a SNOBOL4 pattern which matches "a complete name and international postal mailing address", which is well beyond anything that is practical to even attempt using regular expressions. SNOBOL4 pattern-matching uses a backtracking algorithm similar to that used in the [[logic programming]] language [[Prolog]], which provides pattern-like constructs via [[Definite clause grammar|DCG]]s. This algorithm makes it easier to use SNOBOL as a logic programming language than is the case for most languages. SNOBOL stores variables, strings and data structures in a single [[garbage collection (computer science)|garbage-collected]] heap. == Example programs == The "Hello, World!" program might be as follows... <syntaxhighlight lang=snobol> OUTPUT = "Hello, World!" END </syntaxhighlight> A simple program to ask for a user's name and then use it in an output sentence... <syntaxhighlight lang=snobol> OUTPUT = "What is your name?" Username = INPUT OUTPUT = "Thank you, " Username END </syntaxhighlight> Use :S (branch on successful match) to choose among three possible outputs... <syntaxhighlight lang=snobol> OUTPUT = "What is your name?" Username = INPUT Username "J" :S(LOVE) Username "K" :S(HATE) MEH OUTPUT = "Hi, " Username :(END) LOVE OUTPUT = "How nice to meet you, " Username :(END) HATE OUTPUT = "Oh. It's you, " Username END </syntaxhighlight> To continue requesting input until no more is forthcoming... <syntaxhighlight lang=snobol> OUTPUT = "This program will ask you for personal names" OUTPUT = "until you press return without giving it one" NameCount = 0 :(GETINPUT) AGAIN NameCount = NameCount + 1 OUTPUT = "Name " NameCount ": " PersonalName GETINPUT OUTPUT = "Please give me name " NameCount + 1 PersonalName = INPUT PersonalName LEN(1) :S(AGAIN) OUTPUT = "Finished. " NameCount " names requested." END </syntaxhighlight> == Implementations == The classic implementation was on the [[PDP-10]]; it has been used to study [[compiler]]s, [[formal grammar]]s, and [[artificial intelligence]], especially [[machine translation]] and machine comprehension of [[natural language]]s. The original implementation was on an IBM 7090 at Bell Labs, Holmdel, N.J. SNOBOL4 was specifically designed for portability; the first implementation was started on an IBM 7094 in 1966 but completed on an IBM 360 in 1967. It was rapidly ported to many other platforms. It is normally implemented as an [[interpreter (computer software)|interpreter]] because of the difficulty in implementing some of its very high-level features, but there is a [[compiler]], the [[SPITBOL compiler]], which provides nearly all the facilities that the interpreter provides. The classic implementation on the [[PDP-10]] was quite slow, and in 1972 James Gimpel of Bell Labs, Holmdel, N.J. designed a native implementation of SNOBOL4 for the [[PDP-10]] that he named SITBOL. He used the design as the basis of a graduate class in string processing that he taught that year at [[Stevens Institute of Technology]] (which is why it was named SITBOL). Students were given sections to implement (in PDP-10 assembler) and the entire semester was focused on implementing SITBOL. It was over 80% complete by the end of the semester and was subsequently completed by Professor Gimpel and several students over the summer. SITBOL was a full-featured, high-performance SNOBOL4 interpreter. The [[GNAT]] [[Ada (programming language)|Ada]] Compiler comes with a package (GNAT.Spitbol) that implements all of the Spitbol string manipulation semantics. This can be called from within an Ada program. The file editor for the [[Michigan Terminal System]] (MTS) provided pattern matching based on SNOBOL4 patterns.<ref>[https://books.google.com/books?id=c9BWAAAAMAAJ Introduction to the MTS file editor], University of Michigan Computing Center, 1986.</ref> Several implementations are currently available. Macro SNOBOL4 in C written by Phil Budne is a free, open source implementation, capable of running on almost any platform.<ref>{{cite web| title=SNOBOL4.ORG -- SNOBOL4 Resources |url=http://www.regressive.org/snobol4/}}</ref> Catspaw, Inc provided a commercial implementation of the SNOBOL4 language for many different computer platforms, including DOS, Macintosh, Sun, RS/6000, and others, and these implementations are now available free from Catspaw. Minnesota SNOBOL4, by Viktors Berstis, the closest PC implementation to the original IBM mainframe version (even including Fortran-like FORMAT statement support) is also free.<ref>{{cite web| url=http://www.berstis.com/snobol4.htm |title=The MINNESOTA SNOBOL4 Programming Language}}</ref> Although SNOBOL itself has no [[structured programming]] features, a SNOBOL preprocessor called [[Snostorm]] was designed and implemented during the 1970s by Fred G. Swartz for use under the [[Michigan Terminal System]] (MTS) at the [[University of Michigan]].<ref name=MTSVolume9-June1979>[https://books.google.com/books?id=WxVXAAAAMAAJ&dq=snostorm+preprocessor&pg=PA114 "SNOSTORM"], ''MTS Volume 9: SNOBOL4 in MTS'', Computing Center, University of Michigan, June 1979, pages 99-120. Retrieved 1 September 2014.</ref> Snostorm was used at the eight to fifteen sites that ran MTS. It was also available at [[University College London]] (UCL) between 1982 and 1984. Snocone by [[Andrew Koenig (programmer)|Andrew Koenig]] adds block-structured constructs to the SNOBOL4 language. Snocone is a self-contained programming language, rather than a proper superset of SNOBOL4.<ref>[http://www.snobol4.com/report.htm "The Snocone Programming Language"], Andrew Koenig, USENIX (Portland, Oregon), June 1985. Retrieved 2 September 2014.</ref> The SPITBOL implementation also introduced a number of features which, while not using traditional structured programming keywords, nevertheless can be used to provide many of the equivalent capabilities normally thought of as "structured programming", most notably nested if/then/else type constructs. These features have since been added to most recent SNOBOL4 implementations. After many years as a commercial product, in April 2009 SPITBOL was released as free software under the [[GNU General Public License]]. == Naming == According to Dave Farber,<ref>[http://www.listbox.com/member/archive/247/2008/12/sort/time_rev/page/1/entry/0:180/20081226091150:1B4F85B0-D357-11DD-ABF7-AB09AB975BFC/ WORTH READING Wikipedia entry on SNOBOL {{--}} the TRUE story NOT Wikipedias] (Dave Farber, Interesting People mailing list, 26 December 2008)</ref> he, Griswold and Polonsky "finally arrived at the name Symbolic EXpression Interpreter SEXI." {{Blockquote|All went well until one day I was submitting a batch job to assemble the system and as normal on my JOB [[Punched card|card]] {{--}} the first card in the deck, I, in BTL standards, punched my job and my name {{--}} SEXI Farber. One of the Comp Center girls looked at it and said, "That's what you think" in a humorous way. That made it clear that we needed another name!! We sat and talked and drank coffee and shot rubber bands and after much too much time someone said {{--}} most likely Ralph {{--}} "We don't have a [[wikt:snowball's chance in hell|Snowball's chance in hell]] of finding a name". All of us yelled at once, "WE GOT IT {{--}} SNOBOL" in the spirit of all the [[COBOL|BOL languages]]. We then stretched our mind to find what it stood for.}} Common [[backronym]]s of "SNOBOL" are 'String Oriented Symbolic Language'<ref>''Computers and the humanities'' '''1''':158, 1967.</ref> or (as a [[Acronym and initialism|quasi-initialism]]) 'StriNg Oriented symBOlic Language'.<ref>{{cite book |editor-first=Jack |editor-last=Belzer |editor2-first=Albert G. |editor2-last=Holzman |editor3-first=Allen |editor3-last=Kent |chapter=SNOBOL |chapter-url=https://books.google.com/books?id=CEGXR7FeAWQC&dq=SNOBOL&pg=PA173 |title=Encyclopedia of Computer Science and Technology |publisher=CRC Press |volume=13 |date=1979 |isbn=0-8247-2263-9 |pages=173 }}</ref> == See also == * [[Icon (programming language)]] * [[Snowball (programming language)]] * [[Snostorm]] * [[SPITBOL]] * [[Unicon (programming language)]] == References == {{Reflist}} == Further reading == *{{cite book |first=Mark B. |last=Emmer |title=SNOBOL4+: The SNOBOL4 Language for the Personal Computer User |publisher=Prentice Hall |date=1985 |isbn=0-13-815119-9 }} *{{cite book |first=James F. |last=Gimpel |title=Algorithms in SNOBOL4 |publisher=Wiley |date=1976 |isbn=0-471-30213-9 }} republished Salida, CO: Catspaw, 1986 ({{ISBN|0-939793-00-8}}). *{{cite book |first=Ralph E. |last=Griswold |title=The Macro Implementation of SNOBOL4 |publisher=W.H. Freeman |date=1972 |isbn=0-7167-0447-1 }} *{{cite book |last1=Griswold |first1=Ralph E. |first2=J.F. |last2=Poage |first3=I.P. |last3=Polonsky |title=The SNOBOL4 Programming Language |publisher=Prentice Hall |date=1968 |isbn=0-13-815373-6 }} *{{cite book |first=Ralph E. |last=Griswold |title=String and List Processing in SNOBOL4: Techniques and Applications |publisher=Prentice Hall |date=1975 |isbn=0-13-853010-6 }} *{{cite book |author-link=Susan Hockey |first=Susan M. |last=Hockey |title=Snobol Programming for the Humanities |publisher=Clarendon Press |date=1985 |isbn=0-19-824676-5 }} == External links == * [http://www.regressive.org/snobol4/csnobol4 CSNOBOL4] is a free and open source BSD-licensed port of the original Bell Labs SNOBOL4 to systems with a C compiler, and includes SPITBOL and Blocks enhancements. * [http://www.regressive.org/snobol4/ Catspaw, Inc. offers implementations of and commercial support for SNOBOL4] * {{cite web |title=Oral history interview with Ralph E. Griswold — discusses development of SNOBOL |date= 25 July 1990|publisher=[[Charles Babbage Institute]], University of Minnesota |location=Minneapolis |url=http://purl.umn.edu/107340|last1= Griswold|first1= Ralph E.}} ]. * {{cite web |title=Charles Hall Collection on the SNOBOL Programming Language |date= |publisher=Charles Babbage Institute, University of Minnesota |location=Minneapolis |url=http://purl.umn.edu/40905 }} * [https://www.vintagebigblue.org/Compilerator/SNOBOL4/mvsSnobol4Compile.php For a small brief taste of what SNOBOL4 is about try this online compiler]{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }} * [https://tio.run/#snobol4 Try It Online (Snobol4/CSNOBOL)] Online compiler * [https://tilde.club/~drofmij/snobol/ An introduction to SNOBOL] {{Authority control}} [[Category:Pattern matching programming languages]] [[Category:Programming languages created in 1962]] [[Category:SNOBOL programming language family]] [[Category:Assembly language software]] [[Category:Text-oriented programming languages]] [[Category:Programming languages]] [[Category:Homoiconic programming languages]] [[Category:1962 software]]
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