This branch experiments with adding rules to the chart parser. Currently there are additions that with this strategy

leaf_init = nltk.parse.chart.LeafInitRule()
bottom_up_predict = nltk.parse.chart.BottomUpPredictRule()
double_edge = nltk.parse.chart.DoubleEdgeFundamentalRule()
lexical_single_edge = nltk.parse.chart.LexicalSingleEdgeFundamentalRule()

strategy = [leaf_init,
            lexical_single_edge,
            bottom_up_predict,
            double_edge]

emulate CKY parsing. See notebooks/ckyish.ipynb for an illustration with the stepping chart parser.

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Bird, Steven, Edward Loper and Ewan Klein (2009).
Natural Language Processing with Python.  O'Reilly Media Inc.

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