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A method for transforming grammars into LL(k) form


A new method for transforming grammars into equivalent LL(k) grammars is studied. The applicability of the transformation is characterized by defining a subclass of LR(k) grammars, called predictive LR(k) grammars, with the property that a grammar is predictive LR(k) if and only if the corresponding transformed grammar is LL(k). Furthermore, it is shown that deterministic bottom-up parsing of a predictive LR(k) grammar can be done by the LL(k) parser of the transformed grammar. This parsing method is possible since the transformed grammar always ‘left-to-right covers’ the original grammar. The class of predictive LR(k) grammars strictly includes the class of LC(k) grammars (the grammars that can be parsed deterministically in the left-corner manner). Thus our transformation is more powerful than the one previously available, which transforms LC(k) grammars into LL(k) form.

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Soisalon-Soininen, E., Ukkonen, E. A method for transforming grammars into LL(k) form. Acta Informatica 12, 339–369 (1979).

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Subject Classifications

  • LL(k) grammars
  • parsing of context-free grammars
  • grammatical covering