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Compact non-left-recursive grammars using the selective left-corner transform and factoring

Mark Johnson·Brian Roark
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Abstract

The left-corner transform removes left-recursion from (probabilistic) context-free grammars and unification grammars, permitting simple top-down parsing techniques to be used. Unfortunately the grammars produced by the standard left-corner transform are usually much larger than the original. The selective left-corner transform described in this paper produces a transformed grammar which simulates left-corner recognition of a user-specified set of the original productions, and top-down recognition of the others. Combined with two factorizations, it produces non-left-recursive grammars that are not much larger than the original.

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Mark Johnson, Brian Roark. 2000-08-22. Compact non-left-recursive grammars using the selective left-corner transform and factoring. https://arxiv.org/abs/cs/0008021

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