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Recursive Descent
In computer science, a recursive descent parser is a kind of top-down parser built from a set of mutually recursive procedures (or a non-recursive equivalent) where each such procedure implements one of the nonterminals of the grammar. Thus the structure of the resulting program closely mirrors that of the grammar it recognizes. A ''predictive parser'' is a recursive descent parser that does not require backtracking. Predictive parsing is possible only for the class of LL(''k'') grammars, which are the context-free grammars for which there exists some positive integer ''k'' that allows a recursive descent parser to decide which production to use by examining only the next ''k'' tokens of input. The LL(''k'') grammars therefore exclude all ambiguous grammars, as well as all grammars that contain left recursion. Any context-free grammar can be transformed into an equivalent grammar that has no left recursion, but removal of left recursion does not always yield an LL(''k'') g ... [...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] |
ANTLR
In computer-based language recognition, ANTLR (pronounced ''antler''), or ANother Tool for Language Recognition, is a parser generator that uses a LL(*) algorithm for parsing. ANTLR is the successor to the Purdue Compiler Construction Tool Set (PCCTS), first developed in 1989, and is under active development. Its maintainer is Professor Terence Parr of the University of San Francisco. PCCTS 1.00 was announced April 10, 1992. Usage ANTLR takes as input a grammar that specifies a language and generates as output source code for a recognizer of that language. While Version 3 supported generating code in the programming languages Ada95, ActionScript, C, C#, Java, JavaScript, Objective-C, Perl, Python, Ruby, and Standard ML, Version 4 at present targets C#, C++, Dart, Java, JavaScript, Go, PHP, Python (2 and 3), and Swift. A language is specified using a context-free grammar expressed using Extended Backus–Naur Form (EBNF). ANTLR can generate lexers, parser ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parsing Expression Grammar
In computer science, a parsing expression grammar (PEG) is a type of analytic formal grammar, i.e. it describes a formal language in terms of a set of rules for recognizing strings in the language. The formalism was introduced by Bryan Ford in 2004 and is closely related to the family of top-down parsing languages introduced in the early 1970s. Syntactically, PEGs also look similar to context-free grammars (CFGs), but they have a different interpretation: the choice operator selects the first match in PEG, while it is ambiguous in CFG. This is closer to how string recognition tends to be done in practice, e.g. by a recursive descent parser. Unlike CFGs, PEGs cannot be ambiguous; a string has exactly one valid parse tree or none. It is conjectured that there exist context-free languages that cannot be recognized by a PEG, but this is not yet proven. PEGs are well-suited to parsing computer languages (and artificial human languages such as Lojban) where multiple interpretation a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parboiled (Java)
parboiled is an open-source Java (programming language), Java library released under an Apache License. It provides support for defining Parsing expression grammar, PEG parsers directly in Java source code. parboiled is commonly used as an alternative for regular expressions or parser generators (like ANTLR or JavaCC), especially for smaller and medium-size applications. Apart from providing the constructs for grammar definition parboiled implements a complete recursive descent parser with support for abstract syntax tree construction, parse error reporting and parse error recovery. References External linksOfficial parboiled web site XML software Java (programming language) l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spirit Parser Framework
The Spirit Parser Framework is an object oriented recursive descent parser generator framework implemented using template metaprogramming techniques. Expression templates allow users to approximate the syntax of extended Backus–Naur form (EBNF) completely in C++. Parser objects are composed through operator overloading and the result is a backtracking LL(∞) parser that is capable of parsing rather ambiguous grammars. Spirit can be used for both lexing and parsing, together or separately. This framework is part of the Boost libraries. Operators Because of limitations of the C++ language, the syntax of Spirit has been designed around the operator precedences of C++, while bearing resemblance to both EBNF and regular expressions A regular expression (shortened as regex or regexp), sometimes referred to as rational expression, is a sequence of character (computing), characters that specifies a pattern matching, match pattern in string (computer science), text. Usuall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coco/R
Coco/R is a compiler generator that takes wirth syntax notationIn the manual, however, it is referred as L-attributed Extended Backus–Naur Form syntax (EBNF). grammars of a source language and generates a scanner and a parser for that language. The scanner works as a deterministic finite automaton. It supports Unicode characters in UTF-8 encoding and can be made case-sensitive or case-insensitive. It can also recognize tokens based on their right-hand-side context. In addition to terminal symbols the scanner can also recognize pragmas, which are tokens that are not part of the syntax but can occur anywhere in the input stream (e.g. compiler directives or end-of-line characters). The parser uses recursive descent; LL(1) conflicts can be resolved by either a multi-symbol lookahead or by semantic checks. Thus the class of accepted grammars is LL(k) for an arbitrary k. Fuzzy parsing is supported by so-called ANY symbols that match complementary sets of tokens. Semantic a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TMG (language)
In computing TMG (TransMoGrifier) is a recursive descent compiler-compiler developed by Robert M. McClure and presented in 1965. TMG ran on systems including OS/360 and early Unix. It was used to build EPL, an early version of PL/I. Douglas McIlroy ported TMG to an early version of Unix. According to Ken Thompson, McIlroy wrote TMG in TMG on a piece of paper and "decided to give his piece of paper his piece of paper," hand-compiling assembly language that he entered and assembled on Thompson's Unix system running on PDP-7. Thompson used TMG in 1970 as a tool to offer Fortran, but due to memory limitations of PDP-7 ended up creating the B programming language which was much influenced by BCPL. The recursive descent algorithm of TMG was studied formally by Alexander Birman and Jeffrey Ullman. The formal description of the algorithms was named ''TMG recognition scheme'' (or simply ''TS''). See also * Top-down parsing language * Yacc Yacc (Yet Another Compiler-Compiler) is a co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C (programming Language)
C (''pronounced'' '' – like the letter c'') is a general-purpose programming language. It was created in the 1970s by Dennis Ritchie and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of the targeted Central processing unit, CPUs. It has found lasting use in operating systems code (especially in Kernel (operating system), kernels), device drivers, and protocol stacks, but its use in application software has been decreasing. C is commonly used on computer architectures that range from the largest supercomputers to the smallest microcontrollers and embedded systems. A successor to the programming language B (programming language), B, C was originally developed at Bell Labs by Ritchie between 1972 and 1973 to construct utilities running on Unix. It was applied to re-implementing the kernel of the Unix operating system. During the 1980s, C gradually gained popularity. It has become one of the most widely used programming langu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nonterminal Symbol
In formal languages, terminal and nonterminal symbols are parts of the ''vocabulary'' under a formal grammar. ''Vocabulary'' is a finite, nonempty set of symbols. ''Terminal symbols'' are symbols that cannot be replaced by other symbols of the vocabulary. ''Nonterminal symbols'' are symbols that can be replaced by other symbols of the vocabulary by the production rules under the same formal grammar. A formal grammar defines a formal language over the vocabulary of the grammar. In the context of formal language, the term ''vocabulary'' is more commonly known as ''alphabet''. Nonterminal symbols are also called ''syntactic variables''. Terminal symbols Terminal symbols are those symbols that can appear in the formal language defined by a formal grammar. The process of applying the production rules successively to a start symbol might not terminate, but if it terminates when there is no more production rule can be applied, the output string will consist only of terminal symb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Algorithms + Data Structures = Programs
In mathematics and computer science, an algorithm () is a finite sequence of mathematically rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing calculations and data processing. More advanced algorithms can use conditionals to divert the code execution through various routes (referred to as automated decision-making) and deduce valid inferences (referred to as automated reasoning). In contrast, a heuristic is an approach to solving problems without well-defined correct or optimal results.David A. Grossman, Ophir Frieder, ''Information Retrieval: Algorithms and Heuristics'', 2nd edition, 2004, For example, although social media recommender systems are commonly called "algorithms", they actually rely on heuristics as there is no truly "correct" recommendation. As an effective method, an algorithm can be expressed within a finite amount of space and time"Any classical mathe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
