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LR-attributed Grammar
LR-attributed grammars are a special type of attribute grammars. They allow the attributes to be evaluated on LR parsing. As a result, attribute evaluation in LR-attributed grammars can be incorporated conveniently in bottom-up parsing. zyacc is based on LR-attributed grammars. They are a subset of the L-attributed grammars, where the attributes can be evaluated in one left-to-right traversal of the abstract syntax tree. They are a superset of the S-attributed grammars, which allow only synthesized attributes. In yacc, a common hack is to use global variables to simulate some kind of inherited attributes and thus LR-attribution. External links * http://www.cs.binghamton.edu/~zdu/zyacc/doc/zyacc_4.html * Reinhard Wilhelm Reinhard Wilhelm (born June 5, 1946) is a German computer scientist. Life and work Wilhelm was born in , today part of the municipality of Finnentrop, Westphalia. He studied math, physics and mathematical logic at University of Münster and ...: LL- and LR ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Attribute Grammar
An attribute grammar is a formal way to supplement a formal grammar with semantic information processing. Semantic information is stored in attributes associated with terminal and nonterminal symbols of the grammar. The values of attributes are result of attribute evaluation rules associated with productions of the grammar. Attributes allow to transfer information from anywhere in the abstract syntax tree to anywhere else, in a controlled and formal way. Each semantic function deals with attributes of symbols occurring only in one production rule: both semantic function parameters and its result are attributes of symbols from one particular rule. When a semantic function defines the value of an attribute of the symbol on the left hand side of the rule, the attribute is called ''synthesized''; otherwise it is called ''inherited''. Thus, synthesized attributes serve to pass semantic information up the parse tree, while inherited attributes allow values to be passed from the parent node ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LR Parser
In computer science, LR parsers are a type of 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(1) parsers, Minimal LR(1) parsers, and 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 parse – not a 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 to peek ahead at ''k'' lookahead input symbols before deciding how to parse earlier symbols. Typically ''k'' is 1 and is n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
L-attributed Grammar
L-attributed grammars are a special type of attribute grammars. They allow the attributes to be evaluated in one depth-first left-to-right traversal of the abstract syntax tree. As a result, attribute evaluation in L-attributed grammars can be incorporated conveniently in top-down parsing. A syntax-directed definition is L-attributed if each ''inherited'' attribute of X_j on the right side of A \rightarrow X_1, X_2, \dots, X_n depends only on # the attributes of the symbols X_1, X_2, \dots, X_ # the inherited attributes of A (but not its synthesized attributes) Every S-attributed syntax-directed definition is also L-attributed. Implementing L-attributed definitions in Bottom-Up parsers requires rewriting L-attributed definitions into translation schemes. Many programming languages are L-attributed. Special types of compilers, the narrow compilers, are based on some form of L-attributed grammar. These are a strict superset of S-attributed grammar S-attributed grammars are a c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
S-attributed Grammar
S-attributed grammars are a class of attribute grammars characterized by having no inherited attributes, but only synthesized attributes. Inherited attributes, which must be passed down from parent nodes to children nodes of the abstract syntax tree during the semantic analysis of the parsing process, are a problem for bottom-up parsing because in bottom-up parsing, the parent nodes of the abstract syntax tree are created ''after'' creation of all of their children. Attribute evaluation in S-attributed grammars can be incorporated conveniently in both top-down parsing and bottom-up parsing. Specifications for parser generators in the Yacc family can be broadly considered S-attributed grammars. However, these parser generators usually include the capacity to reference global variables and/or fields from within any given grammar rule, meaning that this is not a ''pure'' S-attributed approach. Any S-attributed grammar is also an L-attributed grammar. See also * Attribute gramma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reinhard Wilhelm
Reinhard Wilhelm (born June 5, 1946) is a German computer scientist. Life and work Wilhelm was born in , today part of the municipality of Finnentrop, Westphalia. He studied math, physics and mathematical logic at University of Münster and computer science at Technical University Munich and Stanford University. He finished his PhD at TU Munich in 1977. In 1978, he obtained a professorship at Saarland University, where he led the chair for programming languages and compiler construction until his retirement in 2014. In addition, Wilhelm has held the post of scientific director of the Leibniz Center for Informatics at Schloss Dagstuhl from its inception in 1990 until 2014. Today he is a professor emeritus at Saarland University. Wilhelm is one of the co-founders of the European Symposium on Programming (ESOP) and the European Joint Conferences on Theory and Practice of Software (ETAPS). The European Association for Programming Languages (EAPLS) goes back to his idea to found a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Formal Languages
In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbol (formal), letters are taken from an alphabet (formal languages), alphabet and are well-formedness, well-formed according to a specific set of rules. The alphabet of a formal language consists of symbols, letters, or tokens that concatenate into strings of the language. Each string concatenated from symbols of this alphabet is called a word, and the words that belong to a particular formal language are sometimes called ''well-formed words'' or ''well-formed formulas''. A formal language is often defined by means of a formal grammar such as a regular grammar or context-free grammar, which consists of its formation rules. In computer science, formal languages are used among others as the basis for defining the grammar of programming languages and formalized versions of subsets of natural languages in which the words of the language represent concepts ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
