 LR parsing became practical when Frank DeRemer invented SLR and LALR parsers with much fewer states.For full details on LR theory and how LR parsers are derived from grammars, see "The Theory of Parsing, Translation, and Compiling, Volume 1" (Aho and Ullman).Earley parsers apply the techniques and notation of LR parsers to the task of generating all possible parses for ambiguous grammars such as for human languages.