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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 In formal language theory, a context-free grammar (CFG) is a formal grammar whose production rules can be applied to a nonterminal symbol regardless of its context. In particular, in a context-free grammar, each production rule is of the for .... 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 th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Science
Computer science is the study of computation, information, and automation. Computer science spans Theoretical computer science, theoretical disciplines (such as algorithms, theory of computation, and information theory) to Applied science, applied disciplines (including the design and implementation of Computer architecture, hardware and Software engineering, software). 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 preventing security vulnerabilities. Computer graphics (computer science), Computer graphics and computational geometry address the generation of images. Programming language theory considers different ways to describe computational processes, and database theory concerns the management of re ... [...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 can be applied to a nonterminal symbol regardless of its context. In particular, in a context-free grammar, each production rule is 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). Regardless of which symbols surround it, the single nonterminal A on the left hand side can always be replaced by \alpha on the right hand side. This distinguishes it from a context-sensitive grammar, which can have production rules in the form \alpha A \beta \rightarrow \alpha \gamma \beta with A a nonterminal symbol and \alpha, \beta, and \gamma strings of terminal and/or nonterminal symbols. 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, : \langl ... [...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 ''Communications of the ACM'' (''CACM'') is the monthly journal of the Association for Computing Machinery (ACM). History It was established in 1958, with Saul Rosen as its first managing editor. It is sent to all ACM members. Articles are i .... 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 (unreachable symbols or unproductive rules) * For each pair of symbols ''X'', ''Y'' (''X' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Viable Prefix
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 or product feature Other uses * Viable Paradise, an annual one-week writing workshop held each autumn on Martha's Vineyard * Viable system m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sentential Form
A formal grammar is a set of symbols and the production rules for rewriting some of them into every possible string of a formal language over an alphabet. A grammar does not describe the meaning of the strings — only their form. In applied mathematics, formal language theory is the discipline that studies formal grammars and languages. 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 determines whether a given string belongs to the language or is grammatically incorrect. To describe such recognizers, formal language theory uses separate formalisms, known as automata theory. One of the interesting resul ... [...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 can be applied to a nonterminal symbol regardless of its context. In particular, in a context-free grammar, each production rule is 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). Regardless of which symbols surround it, the single nonterminal A on the left hand side can always be replaced by \alpha on the right hand side. This distinguishes it from a context-sensitive grammar, which can have production rules in the form \alpha A \beta \rightarrow \alpha \gamma \beta with A a nonterminal symbol and \alpha, \beta, and \gamma strings of terminal and/or nonterminal symbols. 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, : \langl ... [...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 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 \cup V_t)^* \\ X, Y \in (V_n \cup V_t) \end \\ X \lessdot Y &\iff \begin A \to \alpha X B \beta \in P \\ B \Rightarrow^+ Y \gamma \\ A, B \in V_n \\ \alpha , \beta, \gamma \in (V_n \cup V_t)^* \\ X, Y \in (V_n \cup V_t) \end \\ X \gtrdot Y &\iff \beg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lexer (computer Science)
Lexical tokenization is conversion of a text into (semantically or syntactically) meaningful ''lexical tokens'' belonging to categories defined by a "lexer" program. In case of a natural language, those categories include nouns, verbs, adjectives, punctuations etc. In case of a programming language, the categories include identifiers, operators, grouping symbols, data types and language keywords. Lexical tokenization is related to the type of tokenization used in large language models (LLMs) but with two differences. First, lexical tokenization is usually based on a lexical grammar, whereas LLM tokenizers are usually probability-based. Second, LLM tokenizers perform a second step that converts the tokens into numerical values. Rule-based programs A rule-based program, performing lexical tokenization, is called ''tokenizer'', or ''scanner'', although ''scanner'' is also a term for the first stage of a lexer. A lexer forms the first phase of a compiler frontend in processing. Ana ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
