def apply_iter(self, chart, grammar, right_edge):
if (right_edge.is_incomplete() or # use only completed edges
isinstance(right_edge, LeafEdge) or # skip terminal leaves
is_lexical(right_edge) or # skip lexical productions
right_edge.lhs().symbol() == 'G'): # skip BRM rules
return
# We only merge if both the right end left edge are completed. The
# left edge must be adjacent to the right edge in the chart.
for left_edge in chart.select(end=right_edge.start(), is_complete=True):
if isinstance(left_edge, LeafEdge) or is_lexical(left_edge):
continue
new_edge = TreeEdge(span=(left_edge.start(), right_edge.end()),
lhs=right_edge.lhs(),
rhs=[left_edge.lhs(), right_edge.lhs()],
dot=2) # edge is completed at initialization
if chart.insert(new_edge, (left_edge, right_edge)):
yield new_edge
