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SLR Grammar
{{Confusing, date=March 2009 SLR grammars are the class of formal grammars accepted by a Simple LR parser. SLR grammars are a superset of all LR(0) grammars and a subset of all LALR(1) and LR(1) grammars. When processed by an SLR parser, an SLR grammar is converted into parse tables with no shift/reduce or reduce/reduce conflicts for any combination of LR(0) parser state and expected lookahead symbol. If the grammar is not SLR, the parse tables will have shift/reduce conflicts or reduce/reduce conflicts for some state and some lookahead symbols, and the resulting rejected parser is no longer deterministic. The parser cannot decide whether to shift or reduce next, or cannot decide between two candidate reductions. SLR parsers use a Follow(A) calculation to pick the lookahead symbols to expect for every completed nonterminal. LALR parsers use a different calculation which sometimes gives smaller, tighter lookahead sets for the same parser states. Those smaller sets can elimina ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Formal Grammar
A formal grammar is a set of Terminal and nonterminal symbols, symbols and the Production (computer science), production rules for rewriting some of them into every possible string of a formal language over an Alphabet (formal languages), alphabet. A grammar does not describe the semantics, 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 (logic), formal semantics, mathematical logic, and other areas. A formal grammar is a Set_(mathematics), 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 grammatical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Simple LR Parser
In computer science, a Simple LR or SLR parser is a type of LR parser with small parse tables and a relatively simple parser generator algorithm. As with other types of LR(1) parser, an SLR parser is quite efficient at finding the single correct bottom-up parse in a single left-to-right scan over the input stream, without guesswork or backtracking. The parser is mechanically generated from a formal grammar for the language. SLR and the more general methods LALR parser and Canonical LR parser have identical methods and similar tables at parse time; they differ only in the mathematical grammar analysis algorithms used by the parser generator tool. SLR and LALR generators create tables of identical size and identical parser states. SLR generators accept fewer grammars than LALR generators like yacc and Bison. Many computer languages don't readily fit the restrictions of SLR, as is. Bending the language's natural grammar into SLR grammar form requires more compromises and gra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LALR Parser
In computer science, an LALR parser (look-ahead, left-to-right, rightmost derivation parser) is part of the compiling process where human readable text is converted into a structured representation to be read by computers. An LALR parser is a software tool to process (parse) text into a very specific internal representation that other programs, such as compilers, can work with. This process happens according to a set of production rules specified by a formal grammar for a computer language. An LALR parser is a simplified version of a canonical LR parser. The LALR parser was invented by Frank DeRemer in his 1969 PhD dissertation, ''Practical Translators for LR(k) languages'', in his treatment of the practical difficulties at that time of implementing LR(1) parsers. He showed that the LALR parser has more language recognition power than the LR(0) parser, while requiring the same number of states as the LR(0) parser for a language that can be recognized by both parsers. This makes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ambiguous Grammar
In computer science, an ambiguous grammar is a context-free grammar for which there exists a string (computer science), string that can have more than one leftmost derivation or parse tree. Every non-empty context-free language admits an ambiguous grammar by introducing e.g. a duplicate rule. A language that only admits ambiguous grammars is called an #Inherently ambiguous languages, inherently ambiguous language. Deterministic context-free grammars are always unambiguous, and are an important subclass of unambiguous grammars; there are non-deterministic unambiguous grammars, however. For computer programming languages, the reference grammar is often ambiguous, due to issues such as the dangling else problem. If present, these ambiguities are generally resolved by adding precedence rules or other context-sensitive grammar, context-sensitive parsing rules, so the overall phrase grammar is unambiguous. Some parsing algorithms (such as Earley parser, Earley or Generalized LR parser, GL ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Simple LR Parser
In computer science, a Simple LR or SLR parser is a type of LR parser with small parse tables and a relatively simple parser generator algorithm. As with other types of LR(1) parser, an SLR parser is quite efficient at finding the single correct bottom-up parse in a single left-to-right scan over the input stream, without guesswork or backtracking. The parser is mechanically generated from a formal grammar for the language. SLR and the more general methods LALR parser and Canonical LR parser have identical methods and similar tables at parse time; they differ only in the mathematical grammar analysis algorithms used by the parser generator tool. SLR and LALR generators create tables of identical size and identical parser states. SLR generators accept fewer grammars than LALR generators like yacc and Bison. Many computer languages don't readily fit the restrictions of SLR, as is. Bending the language's natural grammar into SLR grammar form requires more compromises and gra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LR Grammar
In computer science, LR parsers are a type of bottom-up parsing, 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 parser, canonical LR(1) parsers, canonical LR parser, minimal LR(1) parsers, and generalized LR parsers (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 parsing, bottom-up parse – not a top-down parsing, 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LL Grammar
In formal language theory, an LL grammar is a context-free grammar that can be parsing, parsed by an LL parser, which parses the input from Left to right, and constructs a Context-free grammar#Derivations and syntax trees, Leftmost derivation of the sentence (hence LL, compared with LR parser that constructs a rightmost derivation). A language that has an LL grammar is known as an LL language. These form subsets of deterministic context-free grammars (DCFGs) and deterministic context-free languages (DCFLs), respectively. One says that a given grammar or language "is an LL grammar/language" or simply "is LL" to indicate that it is in this class. LL parsers are table-based parsers, similar to LR parsers. LL grammars can alternatively be characterized as precisely those that can be parsed by a predictive parser – a recursive descent parser without backtracking – and these can be readily written by hand. This article is about the formal properties of LL grammars; for parsing, see L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
