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Yacc
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). Yacc is supplied as a standard utility on BSD and AT&T Unix. GNU-based Linux distributions include Bison, a forward-compatible Yacc replacement. History 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 (developed using McIlroy's TMG compiler-compiler), 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. Yacc was influenced by and rec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Al Aho
Alfred Vaino Aho (born August 9, 1941) is a Canadian computer scientist best known for his work on programming languages, compilers, and related algorithms, and his textbooks on the art and science of computer programming. Aho was elected into the National Academy of Engineering in 1999 for his contributions to the fields of algorithms and programming tools. He and his long-time collaborator Jeffrey Ullman are the recipients of the 2020 Turing Award, generally recognized as the highest distinction in computer science. Career Aho received a B.A.Sc. (1963) in Engineering Physics from the University of Toronto, then an M.A. (1965) and Ph.D. (1967) in Electrical Engineering/Computer Science from Princeton University. He conducted research at Bell Labs from 1967 to 1991, and again from 1997 to 2002 as Vice President of the Computing Sciences Research Center. Since 1995, he has held the Lawrence Gussman Professorship in Computer Science at Columbia University. He served as chair of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Backus–Naur Form
In computer science, Backus–Naur form (BNF, pronounced ), also known as Backus normal form, is a notation system for defining the Syntax (programming languages), syntax of Programming language, programming languages and other Formal language, formal languages, developed by John Backus and Peter Naur. It is a metasyntax for Context-free grammar, context-free grammars, providing a precise way to outline the rules of a language's structure. It has been widely used in official specifications, manuals, and textbooks on programming language theory, as well as to describe Document format, document formats, Instruction set, instruction sets, and Communication protocol, communication protocols. Over time, variations such as extended Backus–Naur form (EBNF) and augmented Backus–Naur form (ABNF) have emerged, building on the original framework with added features. Structure BNF specifications outline how symbols are combined to form syntactically valid sequences. Each BNF consists of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LALR Parser Generator
A lookahead LR parser (LALR) generator is a software tool that reads a context-free grammar (CFG) and creates an LALR parser which is capable of parsing files written in the context-free language defined by the CFG. LALR parsers are desirable because they are very fast and small in comparison to other types of parsers. There are other types of parser generators, such as Simple LR parser, LR parser, GLR parser, LL parser and GLL parser generators. What differentiates one from another is the type of CFG which they are capable of accepting and the type of parsing algorithm which is used in the generated parser. An LALR parser generator accepts an LALR grammar as input and generates a parser that uses an LALR parsing algorithm (which is driven by LALR parser tables). In practice, LALR offers a good solution, because LALR(1) grammars are more powerful than SLR(1), and can parse most practical LL(1) grammars. LR(1) grammars are more powerful than LALR(1), but ("canonical") LR ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Douglas McIlroy
Malcolm Douglas McIlroy (born 1932) is an American mathematician, engineer, and programmer. As of 2019 he is an Adjunct Professor of Computer Science at Dartmouth College. McIlroy is best known for having originally proposed Unix pipelines and developed several Unix tools, such as echo, spell, diff, sort, join, graph, speak, and tr. He was also one of the pioneering researchers of macro processors and programming language extensibility. He participated in the design of multiple influential programming languages, particularly PL/I, SNOBOL, ALTRAN, TMG and C++. His seminal work on software componentization and code reuse makes him a pioneer of component-based software engineering and software product line engineering. Biography McIlroy earned his bachelor's degree in engineering physics from Cornell University, and a Ph.D. in applied mathematics from MIT in 1959 for his thesis ''On the Solution of the Differential Equations of Conical Shells'' (advisor Eric Reissner). ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LR Parser
In computer science, LR parsers are a type of bottom-up parsing, bottom-up parser that analyse deterministic context-free languages in linear time. There are several variants of LR parsers: SLR parsers, LALR parsers, canonical LR parser, canonical LR(1) parsers, canonical LR parser, minimal LR(1) parsers, and generalized LR parsers (GLR parsers). LR parsers can be generated by a parser generator from a formal grammar defining the syntax of the language to be parsed. They are widely used for the processing of computer languages. An LR parser (left-to-right, rightmost derivation in reverse) reads input text from left to right without backing up (this is true for most parsers), and produces a rightmost derivation in reverse: it does a bottom-up parsing, bottom-up parse – not a top-down parsing, top-down LL parse or ad-hoc parse. The name "LR" is often followed by a numeric qualifier, as in "LR(1)" or sometimes "LR(''k'')". To avoid backtracking or guessing, the LR parser is allowed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix
Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others. Initially intended for use inside the Bell System, AT&T licensed Unix to outside parties in the late 1970s, leading to a variety of both academic and commercial Unix variants from vendors including University of California, Berkeley ( BSD), Microsoft (Xenix), Sun Microsystems ( SunOS/ Solaris), HP/ HPE ( HP-UX), and IBM ( AIX). The early versions of Unix—which are retrospectively referred to as " Research Unix"—ran on computers such as the PDP-11 and VAX; Unix was commonly used on minicomputers and mainframes from the 1970s onwards. It distinguished itself from its predecessors as the first portable operating system: almost the entire operating system is written in the C programming language (in 1973), which allows U ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Portable C Compiler
The Portable C Compiler (also known as pcc or sometimes pccm - portable C compiler machine) is an early compiler for the C programming language written by Stephen C. Johnson of Bell Labs in the mid-1970s, based in part on ideas proposed by Alan Snyder in 1973, and "distributed as ''the'' C compiler by Bell Labs... with the blessing of Dennis Ritchie." Being one of the first compilers that could easily be adapted to output code for different computer architectures, the compiler had a long life span. It debuted in Seventh Edition Unix and shipped with BSD Unix until the release of 4.4BSD in 1994, when it was replaced by the GNU C Compiler. It was very influential in its day, so much so that at the beginning of the 1980s, the majority of C compilers were based on it. Anders Magnusson and Peter A Jonsson restarted development of pcc in 2007, rewriting it extensively to support the C99 standard. Features Key features of pcc are its portability and improved diagnostic capabilitie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Version 3 Unix
Research Unix refers to the early versions of the Unix operating system for DEC PDP-7, PDP-11, VAX and Interdata 7/32 and 8/32 computers, developed in the Bell Labs Computing Sciences Research Center (CSRC). The term ''Research Unix'' first appeared in the Bell System Technical Journal (Vol. 57, No. 6, Part 2 July/August 1978) to distinguish it from other versions internal to Bell Labs (such as PWB/UNIX and MERT) whose code-base had diverged from the primary CSRC version. However, that term was little-used until Version 8 Unix (1985), but has been retroactively applied to earlier versions as well. Prior to V8, the operating system was most commonly called simply UNIX (in caps) or the UNIX Time-Sharing System. Ancient UNIX is any early release of the Unix code base prior to Unix System III, particularly the Research Unix releases prior to and including Version 7 (the base for UNIX/32V as well as later developments of AT&T Unix). History AT&T licensed Version 5 to edu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
B (programming Language)
B is a programming language developed at Bell Labs circa 1969 by Ken Thompson and Dennis Ritchie. B was derived from BCPL, and its name may possibly be a contraction of BCPL. Thompson's coworker Dennis Ritchie speculated that the name might be based on Bon, an earlier, but unrelated, programming language that Thompson designed for use on Multics. B was designed for recursive, non-numeric, machine-independent applications, such as system and language software. It was a typeless language, with the only data type being the underlying machine's natural memory word format, whatever that might be. Depending on the context, the word was treated either as an integer or a memory address. As machines with ASCII processing became common, notably the DEC PDP-11 that arrived at Bell Labs, support for character data stuffed in memory words became important. The typeless nature of the language was seen as a disadvantage, which led Thompson and Ritchie to develop an expanded version of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
AT&T Corporation
AT&T Corporation, an abbreviation for its former name, the American Telephone and Telegraph Company, was an American telecommunications company that provided voice, video, data, and Internet telecommunications and professional services to businesses, consumers, and government agencies. During the Bell System's long history, AT&T was at times the world's largest telecommunications company, the world's largest cable television operator, and a regulated monopoly. At its peak in the 1950s and 1960s, it employed one million people and its revenue ranged between US$3 billion in 1950 ($ in present-day terms) and $12 billion in 1966 ($ in present-day terms). In 2005, AT&T was acquired by " Baby Bell" and former subsidiary SBC Communications for more than $16 billion ($ in present-day terms). SBC then changed its name to AT&T Inc., with AT&T Corporation continuing to exist as a long-distance calling subsidiary until its dissolution on May 1, 2024. History Origins ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exclusive Or
Exclusive or, exclusive disjunction, exclusive alternation, logical non-equivalence, or logical inequality is a logical operator whose negation is the logical biconditional. With two inputs, XOR is true if and only if the inputs differ (one is true, one is false). With multiple inputs, XOR is true if and only if the number of true inputs is odd. It gains the name "exclusive or" because the meaning of "or" is ambiguous when both operands are true. XOR ''excludes'' that case. Some informal ways of describing XOR are "one or the other but not both", "either one or the other", and "A or B, but not A and B". It is symbolized by the prefix operator J Translated as and by the infix operators XOR (, , or ), EOR, EXOR, \dot, \overline, \underline, , \oplus, \nleftrightarrow, and \not\equiv. Definition The truth table of A\nleftrightarrow B shows that it outputs true whenever the inputs differ: Equivalences, elimination, and introduction Exclusive disjunction essentially ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stephen C
Stephen or Steven is an English first name. It is particularly significant to Christians, as it belonged to Saint Stephen ( ), an early disciple and deacon who, according to the Book of Acts, was stoned to death; he is widely regarded as the first martyr (or " protomartyr") of the Christian Church. The name, in both the forms Stephen and Steven, is often shortened to Steve or Stevie. In English, the female version of the name is Stephanie. Many surnames are derived from the first name, including Stephens, Stevens, Stephenson, and Stevenson, all of which mean "Stephen's (son)". In modern times the name has sometimes been given with intentionally non-standard spelling, such as Stevan or Stevon. A common variant of the name used in English is Stephan ( ); related names that have found some currency or significance in English include Stefan (pronounced or in English), Esteban (often pronounced ), and the Shakespearean Stephano ( ). Origins The name "Stephen" ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
