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LR(1)
A canonical LR parser (also called a LR(1) parser) is a type of bottom-up parsing algorithm used in computer science to analyze and process programming languages. It is based on the LR parsing technique, which stands for "left-to-right, rightmost derivation in reverse." Formally, a canonical LR parser is an LR(k) parser for ''k=1'', i.e. with a single lookahead terminal. The special attribute of this parser is that any LR(k) grammar with ''k>1'' can be transformed into an LR(1) grammar. However, back-substitutions are required to reduce k and as back-substitutions increase, the grammar can quickly become large, repetitive and hard to understand. LR(k) can handle all deterministic context-free languages. In the past this LR(k) parser has been avoided because of its huge memory requirements in favor of less powerful alternatives such as the LALR and the LL(1) parser. Recently, however, a "minimal LR(1) parser" whose space requirements are close to LALR parsers, is being offere ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LALR
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] |
LR Parsing
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 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 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 symbol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
