def expand_pushbacks(node):
if not node.elts:
return None
elif all(is_terminal(each) for each in node.elts):
elts = [collect_pushback(_C_(unit(each))) for each in node.elts]
return foldr(conjunction, elts)
else:
raise TypeError(
'Non-terminal in DCG pushback list found: {}'.format(node))
def expand_terminals(node, cont):
if not node.elts:
return cont(None)
elif all(is_terminal(each) for each in node.elts):
*elts, last = (
collect_terminal(_C_(unit(each))) for each in node.elts)
return foldr(conjunction, elts, cont(last))
else:
raise TypeError(
'Non-terminal in DCG terrminal list found: {}'.format(node))