def visit_List(self, node):
if node.elts:
self.push()
*elts, last = node.elts
for each in elts:
self.visit(each)
if is_bitor(last):
self.visit(last.left)
self.visit(last.right)
*items, left, right = self.pop()
cdr = self.cons(left, right)
else:
self.visit(last)
*items, last = self.pop()
cdr = self.cons(last, NIL)
self.append(foldr(self.cons, items, cdr))
else:
self.append(NIL)
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))
def make_list(env, items, tail=NIL):
def cons(*params):
return List(env=env, params=params)
return foldr(cons, items, tail)