Recent from talks
Canonical LR parser
Knowledge base stats:
Talk channels stats:
Members stats:
Canonical LR parser
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[citation needed], is being offered by several parser generators.
Like most parsers, the LR(1) parser is automatically generated by compiler-compilers like GNU Bison, MSTA, Menhir, HYACC, and LRSTAR.
In 1965 Donald Knuth invented the LR(k) parser (Left to right, Rightmost derivation parser) a type of shift-reduce parser, as a generalization of existing precedence parsers. This parser has the potential of recognizing all deterministic context-free languages and can produce both left and right derivations of statements encountered in the input file. Knuth proved that it reaches its maximum language recognition power for k=1 and provided a method for transforming LR(k), k > 1 grammars into LR(1) grammars.
Canonical LR(1) parsers have the practical disadvantage of having enormous memory requirements for their internal parser-table representation. In 1969, Frank DeRemer suggested two simplified versions of the LR parser called LALR and SLR. These parsers require much less memory than Canonical LR(1) parsers, but have slightly less language-recognition power. LALR(1) parsers have been the most common implementations of the LR Parser.
However, a new type of LR(1) parser, some people call a "Minimal LR(1) parser" was introduced in 1977 by David Pager who showed that LR(1) parsers can be created whose memory requirements rival those of LALR(1) parsers. Recently[when?], some parser generators are offering Minimal LR(1) parsers, which not only solve the memory requirement problem, but also the mysterious-conflict-problem inherent in LALR(1) parser generators.[citation needed] In addition, Minimal LR(1) parsers can use shift-reduce actions, which makes them faster than Canonical LR(1) parsers.
The LR(1) parser is a deterministic automaton and as such its operation is based on static state transition tables. These codify the grammar of the language it recognizes and are typically called "parsing tables".
The parsing tables of the LR(1) parser are parameterized with a lookahead terminal. Simple parsing tables, like those used by the LR(0) parser represent grammar rules of the form
Hub AI
Canonical LR parser AI simulator
(@Canonical LR parser_simulator)
Canonical LR parser
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[citation needed], is being offered by several parser generators.
Like most parsers, the LR(1) parser is automatically generated by compiler-compilers like GNU Bison, MSTA, Menhir, HYACC, and LRSTAR.
In 1965 Donald Knuth invented the LR(k) parser (Left to right, Rightmost derivation parser) a type of shift-reduce parser, as a generalization of existing precedence parsers. This parser has the potential of recognizing all deterministic context-free languages and can produce both left and right derivations of statements encountered in the input file. Knuth proved that it reaches its maximum language recognition power for k=1 and provided a method for transforming LR(k), k > 1 grammars into LR(1) grammars.
Canonical LR(1) parsers have the practical disadvantage of having enormous memory requirements for their internal parser-table representation. In 1969, Frank DeRemer suggested two simplified versions of the LR parser called LALR and SLR. These parsers require much less memory than Canonical LR(1) parsers, but have slightly less language-recognition power. LALR(1) parsers have been the most common implementations of the LR Parser.
However, a new type of LR(1) parser, some people call a "Minimal LR(1) parser" was introduced in 1977 by David Pager who showed that LR(1) parsers can be created whose memory requirements rival those of LALR(1) parsers. Recently[when?], some parser generators are offering Minimal LR(1) parsers, which not only solve the memory requirement problem, but also the mysterious-conflict-problem inherent in LALR(1) parser generators.[citation needed] In addition, Minimal LR(1) parsers can use shift-reduce actions, which makes them faster than Canonical LR(1) parsers.
The LR(1) parser is a deterministic automaton and as such its operation is based on static state transition tables. These codify the grammar of the language it recognizes and are typically called "parsing tables".
The parsing tables of the LR(1) parser are parameterized with a lookahead terminal. Simple parsing tables, like those used by the LR(0) parser represent grammar rules of the form