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Simple Precedence Parser
In computer science, a simple precedence parser is a type of bottom-up parser for context-free grammars that can be used only by simple precedence grammars. The implementation of the parser is quite similar to the generic bottom-up parser. A stack is used to store a viable prefix of a sentential form from a rightmost derivation. The symbols ⋖, ≐ and ⋗ are used to identify the pivot, and to know when to Shift or when to Reduce. Implementation * Compute the Wirth–Weber precedence relationship table for a grammar with initial symbol S. * Initialize a stack with the starting marker $. * Append an ending marker $ to the string being parsed (Input). * Until Stack equals "$ S" and Input equals "$" ** Search the table for the relationship between Top(stack) and NextToken(Input) ** if the relationship is ⋖ or ≐ *** Shift: *** Push(Stack, relationship) *** Push(Stack, NextToken(Input)) *** RemoveNextToken(Input) ** if the relationship is ⋗ *** Reduce: *** SearchProductionToRe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Science
Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical disciplines (including the design and implementation of Computer architecture, hardware and Computer programming, software). Computer science is generally considered an area of research, academic research and distinct from computer programming. Algorithms and data structures are central to computer science. The theory of computation concerns abstract models of computation and general classes of computational problem, problems that can be solved using them. The fields of cryptography and computer security involve studying the means for secure communication and for preventing Vulnerability (computing), security vulnerabilities. Computer graphics (computer science), Computer graphics and computational geometry address the generation of images. Progr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bottom-up Parser
Bottom-up may refer to: * Bottom-up analysis, a fundamental analysis technique in accounting and finance * Bottom-up parsing, a computer science strategy * Bottom-up processing, in Pattern recognition (psychology) * Bottom-up theories of galaxy formation and evolution * Bottom-up tree automaton, in data structures * Bottom-up integration testing, in software testing * Top-down and bottom-up design, strategies of information processing and knowledge ordering * Bottom-up proteomics, a laboratory technique involving proteins * Bottom Up Records, a record label founded by Shyheim * Bottom-up approach of the Holocaust, a viewpoint on the causes of the Holocaust See also * Bottoms Up (other) * Top-down (other) * Capsizing, when a boat is turned upside down * Mundanity, an precursor of social movements * Social movements, bottom-up societal reform * Turtling (sailing) In dinghy sailing, a boat is said to be turtling or to turn turtle when the boat is fully invert ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Context-free Grammars
In formal language theory, a context-free grammar (CFG) is a formal grammar whose production rules are of the form :A\ \to\ \alpha with A a ''single'' nonterminal symbol, and \alpha a string of terminals and/or nonterminals (\alpha can be empty). A formal grammar is "context-free" if its production rules can be applied regardless of the context of a nonterminal. No matter which symbols surround it, the single nonterminal on the left hand side can always be replaced by the right hand side. This is what distinguishes it from a context-sensitive grammar. A formal grammar is essentially a set of production rules that describe all possible strings in a given formal language. Production rules are simple replacements. For example, the first rule in the picture, :\langle\text\rangle \to \langle\text\rangle = \langle\text\rangle ; replaces \langle\text\rangle with \langle\text\rangle = \langle\text\rangle ;. There can be multiple replacement rules for a given nonterminal symbol. The l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Simple Precedence Grammar
A simple precedence grammar is a context-free formal grammar that can be parsed with a simple precedence parser. The concept was first created in 1964 by Claude Pair, and was later rediscovered, from ideas due to Robert Floyd, by Niklaus Wirth and Helmut Weber who published a paper, entitled ''EULER: a generalization of ALGOL, and its formal definition'', published in 1966 in the Communications of the ACM. Formal definition G = (''N'', Σ, ''P'', ''S'') is a simple precedence grammar if all the production rules in ''P'' comply with the following constraints: * There are no erasing rules (ε-productions) * There are no useless rules In formal language theory, a context-free grammar (CFG) is a formal grammar whose Production (computer science), production rules are of the form :A\ \to\ \alpha with A a ''single'' nonterminal symbol, and \alpha a string of Terminal and nonter ... (unreachable symbols or unproductive rules) * For each pair of symbols ''X'', ''Y'' (''X'', ''Y ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Viable Prefix
Viability is the ability of a thing (a living organism, an artificial system, an idea, etc.) to maintain itself or recover its potentialities. Viability or viable may refer to: Biology, medicine or ecology * Viability selection, the selection of individual organisms who can survive until they are able to reproduce * Fetal viability, the ability of a fetus to survive outside of the uterus * Genetic viability, chance of a population of plants or animals to avoid the problems of inbreeding * Minimum viable population, a lower bound on the population of a species, such that it can survive in the wild * Population viability analysis, a species-specific method of risk assessment frequently used in conservation biology * Viable count, of viable cells Business * Viability study, a study of the profitability of a business concept which is to be converted into a business * Minimum viable product, in product development, a strategy used for fast and quantitative market testing of a product ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sentential Form
In formal language theory, a grammar (when the context is not given, often called a formal grammar for clarity) describes how to form strings from a language's alphabet that are valid according to the language's syntax. A grammar does not describe the meaning of the strings or what can be done with them in whatever context—only their form. A formal grammar is defined as a set of production rules for such strings in a formal language. Formal language theory, the discipline that studies formal grammars and languages, is a branch of applied mathematics. Its applications are found in theoretical computer science, theoretical linguistics, formal semantics, mathematical logic, and other areas. A formal grammar is a set of rules for rewriting strings, along with a "start symbol" from which rewriting starts. Therefore, a grammar is usually thought of as a language generator. However, it can also sometimes be used as the basis for a "recognizer"—a function in computing that deter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rightmost Derivation
In formal language theory, a context-free grammar (CFG) is a formal grammar whose production rules are of the form :A\ \to\ \alpha with A a ''single'' nonterminal symbol, and \alpha a string of terminals and/or nonterminals (\alpha can be empty). A formal grammar is "context-free" if its production rules can be applied regardless of the context of a nonterminal. No matter which symbols surround it, the single nonterminal on the left hand side can always be replaced by the right hand side. This is what distinguishes it from a context-sensitive grammar. A formal grammar is essentially a set of production rules that describe all possible strings in a given formal language. Production rules are simple replacements. For example, the first rule in the picture, :\langle\text\rangle \to \langle\text\rangle = \langle\text\rangle ; replaces \langle\text\rangle with \langle\text\rangle = \langle\text\rangle ;. There can be multiple replacement rules for a given nonterminal symbol. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wirth–Weber Precedence Relationship
In computer science, a ''Wirth–Weber relationship'' between a pair of symbols (V_t \cup V_n) is necessary to determine if a formal grammar is a simple precedence grammar. In such a case, the simple precedence parser can be used. The relationship is named after computer scientists Niklaus Wirth Niklaus Emil Wirth (born 15 February 1934) is a Swiss computer scientist. He has designed several programming languages, including Pascal (programming language), Pascal, and pioneered several classic topics in software engineering. In 1984, he w ... and Helmut Weber. The goal is to identify when the viable prefixes have the ''pivot'' and must be reduced. A \gtrdot means that the ''pivot'' is found, a \lessdot means that a potential ''pivot'' is starting, and a \doteq means that a relationship remains in the same ''pivot''. Formal definition : G = \langle V_n, V_t, S, P \rangle :: \begin X \doteq Y &\iff \begin A \to \alpha X Y \beta \in P \\ A \in V_n \\ \alpha , \beta \in (V_n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lexer (computer Science)
In computer science, lexical analysis, lexing or tokenization is the process of converting a sequence of characters (such as in a computer program or web page) into a sequence of ''lexical tokens'' (strings with an assigned and thus identified meaning). A program that performs lexical analysis may be termed a ''lexer'', ''tokenizer'', or ''scanner'', although ''scanner'' is also a term for the first stage of a lexer. A lexer is generally combined with a parser, which together analyze the syntax of programming languages, web pages, and so forth. Applications A lexer forms the first phase of a compiler frontend in modern processing. Analysis generally occurs in one pass. In older languages such as ALGOL, the initial stage was instead line reconstruction, which performed unstropping and removed whitespace and comments (and had scannerless parsers, with no separate lexer). These steps are now done as part of the lexer. Lexers and parsers are most often used for compilers, but ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Principles Of Compiler Design
''Principles of Compiler Design'', by Alfred Aho and Jeffrey Ullman, is a classic textbook on compilers for computer programming languages. Both of the authors won the 2020 Turing award for their work on compilers. It is often called the "green dragon book" and its cover depicts a knight and a dragon in battle; the dragon is green, and labeled "Complexity of Compiler Design", while the knight wields a lance and a shield labeled "LALR parser generator" and "Syntax Directed Translation" respectively, and rides a horse labeled "Data Flow Analysis". The book may be called the "green dragon book" to distinguish it from its successor, Aho, Sethi & Ullman's '' Compilers: Principles, Techniques, and Tools'', which is the "red dragon book". The second edition of ''Compilers: Principles, Techniques, and Tools'' added a fourth author, Monica S. Lam, and the dragon became purple; hence becoming the "purple dragon book." The book also contains the entire code for making a compiler. The bac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
