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In computer science, LR parsers are a type of bottom-up parser that analyse deterministic context-free languages in linear time. [1] 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).
Regular languages are a category of languages (sometimes termed Chomsky Type 3) which can be matched by a state machine (more specifically, by a deterministic finite automaton or a nondeterministic finite automaton) constructed from a regular expression.
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.
There is in fact a two-parameter family of LA(k)LR(j) parsers for all combinations of j and k, which can be derived from the LR(j + k) parser, [9] but these do not see practical use. As with other types of LR parsers, an LALR parser is quite efficient at finding the single correct bottom-up parse in a single left-to-right scan over the input ...
These parsers require much less memory than Canonical LR(1) parsers, but have slightly less language-recognition power. [5] 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 [ 6 ] who showed that LR(1 ...
A lookahead LR parser (LALR) generator is a software tool that reads a context-free grammar (CFG) and creates an LALR parser which is capable of parsing files written in the context-free language defined by the CFG. LALR parsers are desirable because they are very fast and small in comparison to other types of parsers.
In 1965, Donald Knuth invented the LR(k) parser and proved that there exists an LR(k) grammar for every deterministic context-free language. [5] This parser still required a lot of memory. In 1969 Frank DeRemer invented the LALR and Simple LR parsers, both based on the LR parser and having greatly reduced memory requirements at the cost of less ...
So bottom-up parsers in practice handle a somewhat larger range of computer language grammars than deterministic top-down parsers do. Bottom-up parsing is sometimes done by backtracking. But much more commonly, bottom-up parsing is done by a shift-reduce parser such as a LALR parser.