def add(self, span_begin, span_end, rule, children):
    """Add an entry to the chart."""
    entry = self.populate_fn(span_begin, span_end, rule, children)
    nonterminal = rule.lhs
    self.key_map[(span_begin, span_end, nonterminal)].extend(entry)
    self.start_map[span_begin].add((span_end, nonterminal))
Add an entry to the chart.
language/compgen/csl/cky/cfg_parser.py