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.
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If a string in the language of the grammar has more than one parsing tree, then the grammar is said to be an " ambiguous grammar ".
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That algorithm was extended to a complete parsing algorithm to accommodate indirect as well as direct left-recursion in polynomial time, and to generate compact polynomial-size representations of the potentially exponential number of parse trees for highly ambiguous grammars by Frost, Hafiz and Callaghan in 2007.
