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{{Short description|Parser generator}}
{{Infobox software
{{Infobox software
| name = Yacc
| name = Yacc
Line 10: Line 11:
| latest release version =
| latest release version =
| latest release date =
| latest release date =
| programming language = [[C (programming language)|C]]
| operating system = [[Unix]], [[Unix-like]], [[Plan 9 from Bell Labs|Plan 9]], [[Inferno (operating system)|Inferno]]
| operating system = [[Unix]], [[Unix-like]], [[Plan 9 from Bell Labs|Plan 9]], [[Inferno (operating system)|Inferno]]
| platform = [[Cross-platform]]
| platform = [[Cross-platform]]
| genre = [[Command (computing)|Command]]
| genre = [[Command (computing)|Command]]
| license =
| license = Plan 9: [[MIT License]]
| website =
| website =
}}
}}
'''Yacc''' ('''Yet Another Compiler-Compiler''') is a [[computer program]] for the [[Unix]] operating system developed by [[Stephen C. Johnson]]. It is a [[LALR parser generator|Look Ahead Left-to-Right (LALR) parser generator]], generating a [[LALR parser]] (the part of a [[compiler]] that tries to make syntactic sense of the [[source code]]) based on an [[formal grammar]], written in a notation similar to [[Backus-Naur form|Backus–Naur Form (BNF)]].<ref>{{cite web |title=The A-Z of Programming Languages: YACC |publisher=Computerworld |url=http://www.techworld.com.au/article/252319/a-z_programming_languages_yacc/ |accessdate=30 November 2012}}</ref> Yacc is supplied as a standard utility on BSD and AT&T Unix.<ref name="Levine 1992 p.xx">{{cite book | last=Levine | first=John | title=Lex & yacc | publisher=O'Reilly & Associates | publication-place=Sebastopol, CA | year=1992 | isbn=1-56592-000-7 | page=xx | url-access=registration | url=https://archive.org/details/lexyacc00levi }}</ref> [[GNU]]-based [[Linux]] distributions include [[GNU bison|Bison]], a forward-compatible Yacc replacement.<ref name="Levine 2009 p.xv">{{cite book | last=Levine | first=John | title=Flex & bison | publisher=O'Reilly Media | publication-place=Sebastopol, Calif | year=2009 | isbn=978-0-596-15597-1 | page=xv}}</ref>
'''Yacc''' ('''Yet Another Compiler-Compiler''') is a [[computer program]] for the [[Unix]] operating system developed by [[Stephen C. Johnson]]. It is a [[LALR parser generator|lookahead left-to-right rightmost derivation (LALR) parser generator]], generating a [[LALR parser]] (the part of a [[compiler]] that tries to make syntactic sense of the [[source code]]) based on a [[formal grammar]], written in a notation similar to [[Backus–Naur form]] (BNF).<ref>{{cite web |title=The A-Z of Programming Languages: YACC |publisher=Computerworld |url=http://www.techworld.com.au/article/252319/a-z_programming_languages_yacc/ |access-date=30 November 2012 |archive-date=31 January 2013 |archive-url=https://web.archive.org/web/20130131031011/http://www.techworld.com.au/article/252319/a-z_programming_languages_yacc/ |url-status=dead }}</ref> Yacc is supplied as a standard utility on BSD and AT&T Unix.<ref name="Levine 1992 p.xx">{{cite book | last=Levine | first=John | title=Lex & yacc | publisher=O'Reilly & Associates | publication-place=Sebastopol, CA | year=1992 | isbn=1-56592-000-7 | page=xx | url-access=registration | url=https://archive.org/details/lexyacc00levi }}</ref> [[GNU]]-based [[Linux]] distributions include [[GNU bison|Bison]], a [[forward-compatible]] Yacc replacement.<ref name="Levine 2009 p.xv">{{cite book | last=Levine | first=John | title=Flex & bison | publisher=O'Reilly Media | publication-place=Sebastopol, Calif | year=2009 | isbn=978-0-596-15597-1 | page=xv}}</ref>


== History ==
== History ==
In the early 1970s, [[Stephen C. Johnson]], a computer scientist at [[Bell Labs]] / [[AT&T Corporation|AT&T]], developed Yacc because he wanted to insert an [[exclusive or]] operator into a [[B (programming language)|B language]] compiler (developed using [[Douglas McIlroy|McIlroy]]'s [[TMG (language)|TMG]] compiler-compiler<ref name="Chistory"/>), but it turned out to be a hard task. As a result, he was directed by Bell Labs colleague [[Al Aho]] to [[Donald Knuth]]'s work on [[LR parser|LR parsing]], which served as the basis for Yacc.<ref name="red">{{cite news|last1=Morris|first1=Richard|title=Stephen Curtis Johnson: Geek of the Week|url=https://www.red-gate.com/simple-talk/opinion/geek-of-the-week/stephen-curtis-johnson-geek-of-the-week/|accessdate=19 January 2018|work=Red Gate Software|date=1 October 2009}}</ref> Yacc was influenced by<ref name="Yacc: Yet Another Compiler-Compiler"/> and received its name in reference to TMG compiler-compiler.<ref>{{cite web|title=Early Translator Writing Systems |url=http://www.chilton-computing.org.uk/acl/applications/cc/p007.htm |publisher=Atlas Computer Laboratory}}</ref>
In the early 1970s, [[Stephen C. Johnson]], a computer scientist at [[Bell Labs]] / [[AT&T Corporation|AT&T]], developed Yacc because he wanted to insert an [[exclusive or]] operator into a [[B (programming language)|B language]] compiler<ref name="red">{{cite news|last1=Morris|first1=Richard|title=Stephen Curtis Johnson: Geek of the Week|url=https://www.red-gate.com/simple-talk/opinion/geek-of-the-week/stephen-curtis-johnson-geek-of-the-week/|access-date=19 January 2018|work=Red Gate Software|date=1 October 2009}}</ref> (developed using [[Douglas McIlroy|McIlroy]]'s [[TMG (language)|TMG]] compiler-compiler<ref name="Chistory"/>), but it turned out to be a hard task. As a result, he was directed by his colleague at Bell Labs [[Al Aho]] to [[Donald Knuth]]'s work on [[LR parser|LR parsing]], which served as the basis for Yacc.<ref name="red">{{cite news|last1=Morris|first1=Richard|title=Stephen Curtis Johnson: Geek of the Week|url=https://www.red-gate.com/simple-talk/opinion/geek-of-the-week/stephen-curtis-johnson-geek-of-the-week/|access-date=19 January 2018|work=Red Gate Software|date=1 October 2009}}</ref> Yacc was influenced by<ref name="Yacc: Yet Another Compiler-Compiler"/> and received its name in reference to TMG compiler-compiler.<ref>{{cite web|title=Early Translator Writing Systems |url=http://www.chilton-computing.org.uk/acl/applications/cc/p007.htm |publisher=Atlas Computer Laboratory}}</ref>


Yacc was originally written in the [[B (programming language)|B programming language]], but was soon rewritten in [[C (programming language)|C]] by Alan Snyder.<ref name="Chistory">{{cite conference
⚫
Yacc was originally written in the [[B (programming language)|B programming language]], but was soon rewritten in [[C (programming language)|C]].<ref name="Chistory">{{cite conference |last=Ritchie |first=Dennis M. |authorlink=Dennis Ritchie |date=April 1993 |title=The Development of the C Language |publisher=Association for Computing Machinery, Inc. |url=http://heim.ifi.uio.no/inf2270/programmer/historien-om-C.pdf }}</ref> It appeared as part of [[Version 3 Unix]],<ref name="reader">{{cite techreport |first1=M. D. |last1=McIlroy |authorlink1=Doug McIlroy |year=1987 |url=http://www.cs.dartmouth.edu/~doug/reader.pdf |title=A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 |series=CSTR |number=139 |institution=Bell Labs}}</ref> and a full description of Yacc was published in 1975.<ref name="Yacc: Yet Another Compiler-Compiler">{{cite techreport |last=Johnson|first=Stephen C.|authorlink=Stephen C. Johnson|year=1975|title=Yacc: Yet Another Compiler-Compiler|number=32|publisher=AT&T Bell Laboratories|location=Murray Hill, New Jersey|url=http://dinosaur.compilertools.net/yacc/|accessdate=31 January 2020}}</ref>
|last=Ritchie
|first=Dennis M.
|author-link=Dennis Ritchie
|date=April 1993
|title=The Development of the C Language
|publisher=Association for Computing Machinery, Inc.
|doi=10.1145/234286.1057834
|doi-access=free
|book-title=History of programming languages---II
|language=en
|isbn=0-201-89502-1
|publication-date=1996-01-01
|quote=After the TMG version of B was working, Thompson rewrote B in itself(a bootstrapping step).…When Johnson returned to Bell Labs in 1973, he was disconcerted to find that the language whose seeds he had brought to Canada had evolved back home; even his own yacc program had been rewritten in C, by Alan Snyder.
|quote-pages=675,684
}}
⚫
</ref> It appeared as part of [[Version 3 Unix]],<ref name="reader">{{cite tech report |first1=M. D. |last1=McIlroy |author-link1=Doug McIlroy |year=1987 |url=http://www.cs.dartmouth.edu/~doug/reader.pdf |title=A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 |series=CSTR |number=139 |institution=Bell Labs}}</ref> and a full description of Yacc was published in 1975.<ref name="Yacc: Yet Another Compiler-Compiler">{{cite tech report |last=Johnson|first=Stephen C.|author-link=Stephen C. Johnson|year=1975|title=Yacc: Yet Another Compiler-Compiler|number=32|publisher=AT&T Bell Laboratories|location=Murray Hill, New Jersey|url=http://dinosaur.compilertools.net/yacc/|access-date=31 January 2020}}</ref>


Johnson used Yacc to create the [[Portable C Compiler]].<ref name="reader"/> [[Bjarne Stroustrup]], on the other hand, attempted to use Yacc for his initial work on [[C++]], but "was defeated by C's syntax" (for example, having both prefix and postfix declaration operators).<ref name="hopl2">{{cite web|last=Stroustrup|first=Bjarne |authorlink=Bjarne Stroustrup |title=A History of C++: 1979−1991|url=http://www.stroustrup.com/hopl2.pdf}}</ref>
Johnson used Yacc to create the [[Portable C Compiler]].<ref name="reader"/> [[Bjarne Stroustrup]] also attempted to use Yacc to create a formal specification of [[C++]], but "was defeated by C's syntax".<ref name="hopl2">{{cite web|last=Stroustrup|first=Bjarne |author-link=Bjarne Stroustrup |title=A History of C++: 1979−1991|url=http://www.stroustrup.com/hopl2.pdf}}</ref> While finding it unsuitable for a formal specification of the language, Stroustrup did proceed to use Yacc to implement [[Cfront]], the first implementation of C++.<ref name="oldcfront">{{cite web|last=Stroustrup|first=Bjarne |author-link=Bjarne Stroustrup |title=Cfront source code|url=http://www.softwarepreservation.org/projects/c_plus_plus/index.html#cfront}}</ref>


In a 2008 interview, Johnson reflected that "the contribution Yacc made to the spread of [[Unix]] and [[C (programming language)|C]] is what I'm proudest of".<ref name="cw">{{
In a 2008 interview, Johnson reflected that "the contribution Yacc made to the spread of [[Unix]] and [[C (programming language)|C]] is what I'm proudest of".<ref name="cw">{{
Line 41: Line 59:
== Description ==
== Description ==
The input to Yacc is a grammar with snippets of [[C (programming language)|C]] code (called "actions") attached to its rules. Its output is a [[shift-reduce parser]] in C that executes the C snippets associated with each rule as soon as the rule is recognized. Typical actions involve the construction of [[parse tree]]s. Using an example from Johnson, if the call {{mono|node(label, left, right)}} constructs a binary parse tree node with the specified {{mono|label}} and children, then the rule
The input to Yacc is a grammar with snippets of [[C (programming language)|C]] code (called "actions") attached to its rules. Its output is a [[shift-reduce parser]] in C that executes the C snippets associated with each rule as soon as the rule is recognized. Typical actions involve the construction of [[parse tree]]s. Using an example from Johnson, if the call {{mono|node(label, left, right)}} constructs a binary parse tree node with the specified {{mono|label}} and children, then the rule
<syntaxhighlight lang="text">
<syntaxhighlight lang="C">
expr : expr '+' expr { $$ = node('+', $1, $3); }
expr : expr '+' expr { $$ = node('+', $1, $3); }
</syntaxhighlight>
</syntaxhighlight>
recognizes summation expressions and constructs nodes for them. The special identifiers {{mono|$$}}, {{mono|$1}} and {{mono|$3}} refer to items on the parser's [[Push-down automaton|stack]].{{r|Yacc: Yet Another Compiler-Compiler}}
recognizes summation expressions and constructs nodes for them. The special identifiers {{mono|$$}}, {{mono|$1}} and {{mono|$3}} refer to items on the parser's [[Push-down automaton|stack]].{{r|Yacc: Yet Another Compiler-Compiler}}


Yacc produces only a parser (phrase analyzer); for full syntactic analysis this requires an external [[lexical analyzer]] to perform the first tokenization stage (word analysis), which is then followed by the parsing stage proper.<ref name="Yacc: Yet Another Compiler-Compiler"/> Lexical analyzer generators, such as [[Lex (software)|Lex]] or [[Flex (lexical analyser generator)|Flex]], are widely available. The [[IEEE]] [[POSIX]] P1003.2 standard defines the functionality and requirements for both Lex and Yacc.<ref>{{man|cu|lex}}, {{man|cu|yacc}}.</ref>
Yacc produces only a parser (phrase analyzer) which can be used alone in the case of [[scannerless parsing]] however, full syntactic analysis typically requires an external [[lexical analyzer]] to perform a tokenization stage first (word analysis), which is then followed by the parsing stage proper.<ref name="Yacc: Yet Another Compiler-Compiler"/> Lexical analyzer generators, such as [[Lex (software)|Lex]] or [[Flex (lexical analyser generator)|Flex]], are widely available for this purpose. The [[IEEE]] [[POSIX]] P1003.2 standard defines the functionality and requirements for both Lex and Yacc.<ref>{{man|cu|lex}}, {{man|cu|yacc}}.</ref>


Some versions of AT&T Yacc have become [[open-source software|open source]]. For example, [[source code]] is available with the standard distributions of [[Plan 9 from Bell Labs|Plan 9]].<ref>{{cite web|title=plan9: UC Berkeley release of Plan 9 under the GPLv2|url=https://github.com/brho/plan9/blob/89d43d2262ad43eb4b26c2a8d6a27cfeddb33828/sys/src/cmd/yacc.c|accessdate=2 January 2018|date=26 December 2017}}</ref>
Some versions of AT&T Yacc have become [[open-source software|open source]]. For example, [[source code]] is available with the standard distributions of [[Plan 9 from Bell Labs|Plan 9]].<ref>{{cite web|title=plan9: UC Berkeley release of Plan 9 under the GPLv2|website=[[GitHub]] |url=https://github.com/brho/plan9/blob/89d43d2262ad43eb4b26c2a8d6a27cfeddb33828/sys/src/cmd/yacc.c|access-date=2 January 2018|date=26 December 2017}}</ref>


== Impact ==
== Impact ==
Yacc and similar programs (largely reimplementations) have been very popular. Yacc itself used to be available as the default parser generator on most Unix systems, though it has since been supplanted by more recent, largely compatible, programs such as [[Berkeley Yacc]], [[GNU bison|GNU Bison]], [[MKS Inc.|MKS]] Yacc, and Abraxas PCYACC. An updated version of the original AT&T version is included as part of [[Sun Microsystems|Sun's]] [[OpenSolaris]] project. Each offers slight improvements and additional features over the original Yacc, but the concept and basic syntax have remained the same.<ref>[https://www.gnu.org/software/bison/manual/html_node/History.html#History Bison Manual: History]</ref>
Yacc and similar programs (largely reimplementations) have been very popular. Yacc itself used to be available as the default parser generator on most Unix systems, though it has since been supplanted by more recent, largely compatible, programs such as [[Berkeley Yacc]], [[GNU bison|GNU Bison]], [[MKS Inc.|MKS]] Yacc, and Abraxas PCYACC. An updated version of the original AT&T Yacc is included as part of [[Sun Microsystems|Sun's]] [[OpenSolaris]] project. Each offers slight improvements and additional features over the original Yacc, but the concept and basic syntax have remained the same.<ref>[https://www.gnu.org/software/bison/manual/html_node/History.html#History Bison Manual: History]</ref>


Yacc was also one of several UNIX tools available for Charles River Data Systems' [[UNOS (operating system)|UNOS]] operating system under [[Bell Laboratories]] license.<ref>{{Cite book|year=1983|title=The Insider's Guide To The Universe|publisher=Charles River Data Systems, Inc.|url=https://www.1000bit.it/ad/bro/charles/CharlesRiverSystem-Universe.pdf|page=13}}</ref>
⚫
Among the languages that were first implemented with Yacc are [[AWK]], [[eqn (software)|eqn]] and [[Pic language|Pic]].<ref>{{cite web|url=https://www.youtube.com/watch?v=vT_J6xc-Az0 |title=UNIX Special: Profs Kernighan & Brailsford |work=Computerphile |date=September 30, 2015 }}</ref> Yacc was also used on Unix to implement the [[Portable C Compiler]], as well as parsers for such programming languages as [[FORTRAN 77]], [[Ratfor]], [[APL (programming language)|APL]], [[bc (programming language)|bc]], [[m4 (computer language)|m4]], etc.<ref name="reader"/><ref>{{cite book|last1=Kernighan|first1=Brian W.|last2=Pike|first2=Rob|title=[[The Unix Programming Environment]]|year=1984|publisher=Prentice Hall|isbn=0-13-937681-X}}</ref>


⚫
Among the languages that were first implemented with Yacc are [[AWK]], [[C++]],<ref name="oldcfront">{{cite web|last=Stroustrup|first=Bjarne |author-link=Bjarne Stroustrup |title=Cfront source code|url=http://www.softwarepreservation.org/projects/c_plus_plus/index.html#cfront}}</ref> [[eqn (software)|eqn]] and [[Pic language|Pic]].<ref>{{cite web|url=https://www.youtube.com/watch?v=vT_J6xc-Az0 |archive-url=https://ghostarchive.org/varchive/youtube/20211211/vT_J6xc-Az0| archive-date=2021-12-11 |url-status=live|title=UNIX Special: Profs Kernighan & Brailsford |work=Computerphile |date=September 30, 2015 }}{{cbignore}}</ref> Yacc was also used on Unix to implement the [[Portable C Compiler]], as well as parsers for such programming languages as [[FORTRAN 77]], [[Ratfor]], [[APL (programming language)|APL]], [[bc (programming language)|bc]], [[m4 (computer language)|m4]], etc.<ref name="reader"/><ref>{{cite book|last1=Kernighan|first1=Brian W.|last2=Pike|first2=Rob|title=[[The Unix Programming Environment]]|year=1984|publisher=Prentice Hall|isbn=0-13-937681-X}}</ref>
⚫
Yacc has also been rewritten for other languages, including [[OCaml]],<ref>{{cite web |title=OCaml User's Manual: Chapter 12 Lexer and parser generators (ocamllex, ocamlyacc) |url=http://caml.inria.fr/pub/docs/manual-ocaml-4.00/manual026.html |accessdate=25 Nov 2013}}</ref> [[Ratfor]], [[ML programming language|ML]], [[Ada (programming language)|Ada]], [[Pascal (programming language)|Pascal]], [[Java (programming language)|Java]], [[Python (programming language)|Python]], [[Ruby (programming language)|Ruby]], [[Go (programming language)|Go]],<ref>{{cite web |title=Yacc.go: A version of Yacc for the Go Programming Language |url=https://godoc.org/golang.org/x/tools/cmd/goyacc |accessdate=15 July 2017}}</ref>, [[Common Lisp]]<ref>{{cite web|title=CL-Yacc: A Common Lisp version of Yacc |url=http://www.pps.univ-paris-diderot.fr/~jch/software/cl-yacc/}}</ref> and [[Erlang (programming language)|Erlang]].<ref>{{cite web |title=yecc: An Erlang implementation of Yacc |url=http://erlang.org/doc/man/yecc.html}}</ref>

⚫
Yacc has also been rewritten for other languages, including [[OCaml]],<ref>{{cite web |title=OCaml User's Manual: Chapter 12 Lexer and parser generators (ocamllex, ocamlyacc) |url=http://caml.inria.fr/pub/docs/manual-ocaml-4.00/manual026.html |access-date=25 Nov 2013}}</ref> [[Ratfor]], [[ML programming language|ML]], [[Ada (programming language)|Ada]], [[Pascal (programming language)|Pascal]], [[Java (programming language)|Java]], [[PHP]], [[Python (programming language)|Python]], [[Ruby (programming language)|Ruby]], [[Go (programming language)|Go]],<ref>{{cite web |title=Yacc.go: A version of Yacc for the Go Programming Language |url=https://godoc.org/golang.org/x/tools/cmd/goyacc |access-date=15 July 2017}}</ref> [[Common Lisp]]<ref>{{cite web|title=CL-Yacc: A Common Lisp version of Yacc |url=http://www.pps.univ-paris-diderot.fr/~jch/software/cl-yacc/}}</ref> and [[Erlang (programming language)|Erlang]].<ref>{{cite web |title=yecc: An Erlang implementation of Yacc |url=http://erlang.org/doc/man/yecc.html}}</ref>


* [[Berkeley Yacc]]: The Berkeley implementation of Yacc quickly became more popular than AT&T Yacc itself because of its performance and lack of reuse restrictions.<ref>{{citation |title=flex & bison |author=John Levine |publisher=O'Reilly Media |date=August 2009 }}</ref>
* [[Berkeley Yacc]]: The Berkeley implementation of Yacc quickly became more popular than AT&T Yacc itself because of its performance and lack of reuse restrictions.<ref>{{citation |title=flex & bison |author=John Levine |publisher=O'Reilly Media |date=August 2009 }}</ref>
Line 72: Line 92:


==External links==
==External links==
* [https://pacc.interitty.org Playground] environment for learning and testing syntax

{{Wikibooks|Guide to Unix|Commands}}
{{Wikibooks|Guide to Unix|Commands}}
* {{man|cu|yacc|SUS}}
* {{man|cu|yacc|SUS}}
* {{man|1|yacc|Plan 9}}
* {{man|1|yacc|Plan 9}}
* {{man|1|yacc|Inferno}}
* {{man|1|yacc|Inferno}}
* {{man|1|yacc|ManKier}}


{{Unix commands}}
{{Unix commands}}
{{Plan 9 commands}}

{{Authority control}}


[[Category:Compiling tools]]
[[Category:Compiling tools]]

Latest revision as of 21:29, 2 August 2024

Yacc
Original author(s)Stephen C. Johnson
Repository
Written inC
Operating systemUnix, Unix-like, Plan 9, Inferno
PlatformCross-platform
TypeCommand
LicensePlan 9: MIT License

Yacc (Yet Another Compiler-Compiler) is a computer program for the Unix operating system developed by Stephen C. Johnson. It is a lookahead left-to-right rightmost derivation (LALR) parser generator, generating a LALR parser (the part of a compiler that tries to make syntactic sense of the source code) based on a formal grammar, written in a notation similar to Backus–Naur form (BNF).[1] Yacc is supplied as a standard utility on BSD and AT&T Unix.[2] GNU-based Linux distributions include Bison, a forward-compatible Yacc replacement.[3]

History

[edit]

In the early 1970s, Stephen C. Johnson, a computer scientist at Bell Labs / AT&T, developed Yacc because he wanted to insert an exclusive or operator into a B language compiler[4] (developed using McIlroy's TMG compiler-compiler[5]), but it turned out to be a hard task. As a result, he was directed by his colleague at Bell Labs Al Aho to Donald Knuth's work on LR parsing, which served as the basis for Yacc.[4] Yacc was influenced by[6] and received its name in reference to TMG compiler-compiler.[7]

Yacc was originally written in the B programming language, but was soon rewritten in C by Alan Snyder.[5] It appeared as part of Version 3 Unix,[8] and a full description of Yacc was published in 1975.[6]

Johnson used Yacc to create the Portable C Compiler.[8] Bjarne Stroustrup also attempted to use Yacc to create a formal specification of C++, but "was defeated by C's syntax".[9] While finding it unsuitable for a formal specification of the language, Stroustrup did proceed to use Yacc to implement Cfront, the first implementation of C++.[10]

In a 2008 interview, Johnson reflected that "the contribution Yacc made to the spread of Unix and C is what I'm proudest of".[11]

Description

[edit]

The input to Yacc is a grammar with snippets of C code (called "actions") attached to its rules. Its output is a shift-reduce parser in C that executes the C snippets associated with each rule as soon as the rule is recognized. Typical actions involve the construction of parse trees. Using an example from Johnson, if the call node(label, left, right) constructs a binary parse tree node with the specified label and children, then the rule 

expr : expr '+' expr  { $$ = node('+', $1, $3); }

recognizes summation expressions and constructs nodes for them. The special identifiers $$, $1 and $3 refer to items on the parser's stack.[6]

Yacc produces only a parser (phrase analyzer) which can be used alone in the case of scannerless parsing however, full syntactic analysis typically requires an external lexical analyzer to perform a tokenization stage first (word analysis), which is then followed by the parsing stage proper.[6] Lexical analyzer generators, such as Lex or Flex, are widely available for this purpose. The IEEE POSIX P1003.2 standard defines the functionality and requirements for both Lex and Yacc.[12]

Some versions of AT&T Yacc have become open source. For example, source code is available with the standard distributions of Plan 9.[13]

Impact

[edit]

Yacc and similar programs (largely reimplementations) have been very popular. Yacc itself used to be available as the default parser generator on most Unix systems, though it has since been supplanted by more recent, largely compatible, programs such as Berkeley Yacc, GNU Bison, MKS Yacc, and Abraxas PCYACC. An updated version of the original AT&T Yacc is included as part of Sun's OpenSolaris project. Each offers slight improvements and additional features over the original Yacc, but the concept and basic syntax have remained the same.[14]

Yacc was also one of several UNIX tools available for Charles River Data Systems' UNOS operating system under Bell Laboratories license.[15]

Among the languages that were first implemented with Yacc are AWK, C++,[10] eqn and Pic.[16] Yacc was also used on Unix to implement the Portable C Compiler, as well as parsers for such programming languages as FORTRAN 77, Ratfor, APL, bc, m4, etc.[8][17]

Yacc has also been rewritten for other languages, including OCaml,[18] Ratfor, ML, Ada, Pascal, Java, PHP, Python, Ruby, Go,[19] Common Lisp[20] and Erlang.[21]

  • Berkeley Yacc: The Berkeley implementation of Yacc quickly became more popular than AT&T Yacc itself because of its performance and lack of reuse restrictions.[22]
  • LALR parser: The underlying parsing algorithm in Yacc-generated parsers.
  • Bison: The GNU version of Yacc.
  • Lex (and Flex lexical analyser), a token parser commonly used in conjunction with Yacc (and Bison).
  • BNF is a metasyntax used to express context-free grammars: that is a formal way to describe context-free languages.
  • PLY (Python Lex-Yacc) is an alternative implementation of Lex and Yacc in Python.

See also

[edit]

References

[edit]
  1. ^ "The A-Z of Programming Languages: YACC". Computerworld. Archived from the original on 31 January 2013. Retrieved 30 November 2012.
  2. ^ Levine, John (1992). Lex & yacc. Sebastopol, CA: O'Reilly & Associates. p. xx. ISBN 1-56592-000-7.
  3. ^ Levine, John (2009). Flex & bison. Sebastopol, Calif: O'Reilly Media. p. xv. ISBN 978-0-596-15597-1.
  4. ^ a b Morris, Richard (1 October 2009). "Stephen Curtis Johnson: Geek of the Week". Red Gate Software. Retrieved 19 January 2018.
  5. ^ a b Ritchie, Dennis M. (April 1993). "The Development of the C Language". History of programming languages---II. Association for Computing Machinery, Inc. (published 1996-01-01). doi:10.1145/234286.1057834. ISBN 0-201-89502-1. pp. 675, 684: After the TMG version of B was working, Thompson rewrote B in itself(a bootstrapping step).…When Johnson returned to Bell Labs in 1973, he was disconcerted to find that the language whose seeds he had brought to Canada had evolved back home; even his own yacc program had been rewritten in C, by Alan Snyder.
  6. ^ a b c d Johnson, Stephen C. (1975). Yacc: Yet Another Compiler-Compiler (Technical report). Murray Hill, New Jersey: AT&T Bell Laboratories. 32. Retrieved 31 January 2020.
  7. ^ "Early Translator Writing Systems". Atlas Computer Laboratory.
  8. ^ a b c McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. 139.
  9. ^ Stroustrup, Bjarne. "A History of C++: 1979−1991" (PDF).
  10. ^ a b Stroustrup, Bjarne. "Cfront source code".
  11. ^ Hamilton, Naomi (2008-07-09). "Yacc, Unix, and advice from Bell Labs alumni Stephen Johnson". www.computerworld.com. Archived from the original on 2020-08-22. Retrieved 2020-11-10.
  12. ^ lex – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group, yacc – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group.
  13. ^ "plan9: UC Berkeley release of Plan 9 under the GPLv2". GitHub. 26 December 2017. Retrieved 2 January 2018.
  14. ^ Bison Manual: History
  15. ^ The Insider's Guide To The Universe (PDF). Charles River Data Systems, Inc. 1983. p. 13.
  16. ^ "UNIX Special: Profs Kernighan & Brailsford". Computerphile. September 30, 2015. Archived from the original on 2021-12-11.
  17. ^ Kernighan, Brian W.; Pike, Rob (1984). The Unix Programming Environment. Prentice Hall. ISBN 0-13-937681-X.
  18. ^ "OCaml User's Manual: Chapter 12 Lexer and parser generators (ocamllex, ocamlyacc)". Retrieved 25 Nov 2013.
  19. ^ "Yacc.go: A version of Yacc for the Go Programming Language". Retrieved 15 July 2017.
  20. ^ "CL-Yacc: A Common Lisp version of Yacc".
  21. ^ "yecc: An Erlang implementation of Yacc".
  22. ^ John Levine (August 2009), flex & bison, O'Reilly Media
[edit]
  • Playground environment for learning and testing syntax
The Wikibook Guide to Unix has a page on the topic of: Commands
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