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Earley parser
In computer science, the Earley parser is an algorithm for parsing strings that belong to a given context-free language, though (depending on the variant) it may suffer problems with certain nullable grammars. The algorithm, named after its inventor, Jay Earley, is a chart parser that uses dynamic programming; it is mainly used for parsing in computational linguistics. It was first introduced in his dissertation in 1968 (and later appeared in abbreviated, more legible form in a journal).
Earley parsers are appealing because they can parse all context-free languages, unlike LR parsers and LL parsers, which are more typically used in compilers but which can only handle restricted classes of languages. The Earley parser executes in cubic time in the general case , where ''n'' is the length of the parsed string, quadratic time for unambiguous grammars , and linear time for almost all LR(k) grammars. It performs particularly well when the rules are written left-recursively.
== Earley recogniser ==
The following algorithm describes the Earley recogniser. The recogniser can be easily modified to create a parse tree as it recognises, and in that way can be turned into a parser.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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