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<Paper uid="C00-1052">
  <Title>Compact non-left-recursive grammars using the selective left-corner transform and factoring*</Title>
  <Section position="5" start_page="514" end_page="514" type="concl">
    <SectionTitle>
4 Conclusion
</SectionTitle>
    <Paragraph position="0"> This paper presented factored selective left-corner grammar transtbrms. These transtbrlns preserve the priinary benefits of the left-conmr grammar transform (i.e., elimination of left-recursion and preservation of annotations on tlroductions) while dranmtitally ameliorating its 1)rincipal problems (gramnmr size and sparse data problelns). This should extend the applicability of left-conmr techniques to situations involving large grammars. We showed how to identif~y the nfinimal set L0 of productions of a grammar that must be recognized left-corner ill order for the transformed grammar not to be left-recursive.</Paragraph>
    <Paragraph position="1"> We also proposed two factorizations of tile output of the selective left-corner grmnmar t, ransfbrm which fllrther reduce grammar size, and showed that there is only a nfinor increase in gralnmar size when the  B~ctored sele(:tive left-corner transform is apl)lied to a large tre('A)a.nk grmnmar. Finally, we exploited the tree trm~sforms that, correspond to these grammar trmlsforms to formulate and study a class of sto(:hastie generalized left-corner t)arsers.</Paragraph>
    <Paragraph position="2"> This work could be extended in a. nmnber of ways.</Paragraph>
    <Paragraph position="3"> D)r examl)le, in this t)al)er we assumed that one would always choose a left-corner l)ro(lut'tioll set that inehtdes the nfinimal set L0 required to ensure that the transfbrmed grammar is not left-recursive.</Paragraph>
    <Paragraph position="4"> However, Roark mid Johnson (1999) report good perR)rmance from a stochastically-guided top-down parser, suggesting that lefl;-recm'sion is not; always fatal. It might be possible to judiciously choose a M't-cor,mr production set smaller than L0 which elimiimtes t)erni(:ious left-r(;cursion, so that the remaining lefl;-reeursive cycles llav(', su(:h low t)rol)a1)ility that tlmy will efl'(~(:t;ively never l)e used and a stochastically-guided top-down l)arser will II(~,Vel ' sea.reh l;h(un.</Paragraph>
  </Section>
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