|
Recursive Descent
In computer science, a recursive descent parser is a kind of top-down parsing, top-down parser built from a set of mutual recursion, mutually recursive procedures (or a non-recursive equivalent) where each such procedure (computer science), procedure implements one of the Terminal and nonterminal symbols, nonterminals of the formal grammar, 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 parser, 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 ... [...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] |
ANTLR
In computer-based language recognition, ANTLR (pronounced ''antler''), or ANother Tool for Language Recognition, is a parser generator that uses LL(*) 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. 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, parsers, tree parsers, and combined lexer-parsers. Parsers can ... [...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), but not natural languages where th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parboiled (Java)
parboiled is an open-source Java library released under an Apache License. It provides support for defining 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. Example Since parsing with parboiled does not require a separate lexing phase and there is no special syntax to learn for grammar definition parboiled makes it comparatively easy to build custom parsers quickly. Consider this the following classic "calculator" example, with these rules in a simple pseudo notation With parboiled this rule description can be translated directly into the following Java code: import org.parboiled.BaseParser; public cla ... [...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 characters that specifies a search pattern in text. Usually such patterns are used by string-searching algorithms for "find" or ... [...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 acti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
JavaCC
JavaCC (Java Compiler Compiler) is an open-source parser generator and lexical analyzer generator written in the Java programming language. JavaCC is similar to yacc in that it generates a parser from a formal grammar written in EBNF notation. Unlike yacc, however, JavaCC generates top-down parsers. JavaCC can resolve choices based on the next ''k'' input tokens, and so can handle LL(''k'') grammars automatically; by use of "lookahead specifications", it can also resolve choices requiring unbounded look ahead. JavaCC also generates lexical analyzers in a fashion similar to lex. The tree builder that accompanies it, JJTree, constructs its trees from the bottom up. JavaCC is licensed under a BSD license. History In 1996, Sun Microsystems released a parser generator called ''Jack''. The developers responsible for ''Jack'' created their own company called Metamata and changed the ''Jack'' name to JavaCC. Metamata eventually became part of WebGain. After WebGain shut down its ope ... [...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 comp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C (programming Language)
C (''pronounced like the letter c'') is a General-purpose language, general-purpose computer 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 CPUs. It has found lasting use in operating systems, device drivers, protocol stacks, though decreasingly for application software. 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 measuring programming language popularity, most widely used programming languages, with C compilers avail ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nonterminal Symbol
In computer science, terminal and nonterminal symbols are the lexical elements used in specifying the production rules constituting a formal grammar. ''Terminal symbols'' are the elementary symbols of the language defined by a formal grammar. ''Nonterminal symbols'' (or ''syntactic variables'') are replaced by groups of terminal symbols according to the production rules. The terminals and nonterminals of a particular grammar are two disjoint sets. Terminal symbols Terminal symbols are literal symbols that may appear in the outputs of the production rules of a formal grammar and which cannot be changed using the rules of the grammar. Applying the rules recursively to a source string of symbols will usually terminate in a final output string consisting only of terminal symbols. Consider a grammar defined by two rules. Using pictoric marks interacting with each other: # The symbol ר can become ди # The symbol ר can become д Here д is a terminal symbol because no rule ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Terminal Symbol
In computer science, terminal and nonterminal symbols are the lexical elements used in specifying the production rules constituting a formal grammar. ''Terminal symbols'' are the elementary symbols of the language defined by a formal grammar. ''Nonterminal symbols'' (or ''syntactic variables'') are replaced by groups of terminal symbols according to the production rules. The terminals and nonterminals of a particular grammar are two disjoint sets. Terminal symbols Terminal symbols are literal symbols that may appear in the outputs of the production rules of a formal grammar and which cannot be changed using the rules of the grammar. Applying the rules recursively to a source string of symbols will usually terminate in a final output string consisting only of terminal symbols. Consider a grammar defined by two rules. Using pictoric marks interacting with each other: # The symbol ר can become ди # The symbol ר can become д Here д is a terminal symbol because no rule ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Algorithms + Data Structures = Programs
In mathematics and computer science, an algorithm () is a finite sequence of 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 perform automated deductions (referred to as automated reasoning) and use mathematical and logical tests to divert the code execution through various routes (referred to as automated decision-making). Using human characteristics as descriptors of machines in metaphorical ways was already practiced by Alan Turing with terms such as "memory", "search" and "stimulus". In contrast, a heuristic is an approach to problem solving that may not be fully specified or may not guarantee correct or optimal results, especially in problem domains where there is no well-defined correct or optimal result. As an effective method, an algorithm can be expressed within a finite amount of space and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
