Recursive Ascent

Abstract

A recursive descent recognizer for F _G is called a recursive ascent recognizer for G. The algorithm is akin to the Earley algorithm, itself discussed in section 7.5 of the next chapter, if the functions are memoized, especially if the algorithm is implemented in the interpretative way (see the discussion following (4.6)). The compiled implementation is potentially more efficient than the standard Earley algorithm. Deterministic recursive descent recognizers with look ahead, as in section 4.4, applied to grammars like F _g , are called PLR(k) recognizers in the literature. Our algorithm could thus be called a “PLR(0)-like recognizer,” but it could also be called a nondeterministic left-comer recognizer, following yet another nomenclature from the world of deterministic parsing methods. From all potential names we choose to call the kind of algorithms we are now engaged in “Earley-like” or “recursive ascent Earley” parsers, to emphasize the nondeterministic nature of the algorithms and the fact that they are item-based.