Removing left recursion from context-free grammars

  • Authors:
  • Robert C. Moore

  • Affiliations:
  • Microsoft Research, Redmond, Washington

  • Venue:
  • NAACL 2000 Proceedings of the 1st North American chapter of the Association for Computational Linguistics conference
  • Year:
  • 2000

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Abstract

A long-standing issue regarding algorithms that manipulate context-free grammars (CFGs) in a "top-down" left-to-right fashion is that left recursion can lead to nontermination. An algorithm is known that transforms any CFG into an equivalent nonleft-recursive CFG, but the resulting grammars are often too large for practical use. We present a new method for removing left recursion from CFGs that is both theoretically superior to the standard algorithm, and produces very compact non-left-recursive CFGs in practice.