Editing LALR parser (section)

== Overview ==
Generally, the LALR parser refers to the LALR(1) parser,{{efn|"LALR(1)" is pronounced as the [[initialism]] "el-ay-el-arr-one"}} just as the LR parser generally refers to the LR(1) parser. The "(1)" denotes one-token lookahead, to resolve differences between rule patterns during parsing. Similarly, there is an LALR(2) parser with two-token lookahead, and LALR(''k'') parsers with ''k''-token lookup, but these are rare in actual use. The LALR parser is based on the LR(0) parser, so it can also be denoted LALR(1)&nbsp;=&nbsp;LA(1)LR(0) (1 token of lookahead, LR(0)) or more generally LALR(''k'')&nbsp;=&nbsp;LA(''k'')LR(0) (k tokens of lookahead, LR(0)). 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''&nbsp;+&nbsp;''k'') parser,<ref>''Parsing Techniques: A Practical Guide,'' by Dick Grune and Ceriel J. H. Jacobs, "9.7 LALR(1)", [https://books.google.com/books?id=05xA_d5dSwAC&pg=PA302 p. 302]</ref> 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 parsing|bottom-up parse]] in a single left-to-right scan over the input stream, because it does not need to use [[backtracking]]. Being a lookahead parser by definition, it always uses a lookahead, with {{nowrap|LALR(1)}} being the most-common case.