pypy translate error

error message

[translation:ERROR] Error:
[translation:ERROR]  Traceback (most recent call last):
[translation:ERROR]    File "../pypy/pypy/translator/goal/translate.py", line 308, in main
[translation:ERROR]     drv.proceed(goals)
[translation:ERROR]    File "/Users/neppord/pypy/pypy/translator/driver.py", line 810, in proceed
[translation:ERROR]     return self._execute(goals, task_skip = self._maybe_skip())
[translation:ERROR]    File "/Users/neppord/pypy/pypy/translator/tool/taskengine.py", line 116, in _execute
[translation:ERROR]     res = self._do(goal, taskcallable, *args, **kwds)
[translation:ERROR]    File "/Users/neppord/pypy/pypy/translator/driver.py", line 286, in _do
[translation:ERROR]     res = func()
[translation:ERROR]    File "/Users/neppord/pypy/pypy/translator/driver.py", line 371, in task_rtype_lltype
[translation:ERROR]     crash_on_first_typeerror=insist)
[translation:ERROR]    File "/Users/neppord/pypy/pypy/rpython/rtyper.py", line 211, in specialize
[translation:ERROR]     self.specialize_more_blocks()
[translation:ERROR]    File "/Users/neppord/pypy/pypy/rpython/rtyper.py", line 254, in specialize_more_blocks
[translation:ERROR]     self.specialize_block(block)
[translation:ERROR]    File "/Users/neppord/pypy/pypy/rpython/rtyper.py", line 408, in specialize_block
[translation:ERROR]     self.gottypererror(e, block, hop.spaceop, newops)
[translation:ERROR]    File "/Users/neppord/pypy/pypy/rpython/rtyper.py", line 406, in specialize_block
[translation:ERROR]     self.translate_hl_to_ll(hop, varmapping)
[translation:ERROR]    File "/Users/neppord/pypy/pypy/rpython/rtyper.py", line 535, in translate_hl_to_ll
[translation:ERROR]     resultvar = hop.dispatch()
[translation:ERROR]    File "/Users/neppord/pypy/pypy/rpython/rtyper.py", line 768, in dispatch
[translation:ERROR]     return translate_meth(self)
[translation:ERROR]    File "<336-codegen /Users/neppord/pypy/pypy/rpython/rtyper.py:620>", line 5, in translate_op_ne
[translation:ERROR]     return pair(r_arg1, r_arg2).rtype_ne(hop)
[translation:ERROR]    File "/Users/neppord/pypy/pypy/rpython/rmodel.py", line 311, in missing_rtype_operation
[translation:ERROR]     "'%s' on %r" % (opname, self))
[translation:ERROR]  MissingRTypeOperation: unimplemented operation: 'ne' on (<InstanceRepr for main.AckermanNode>, <NoneFrozenPBCRepr Void>)
[translation:ERROR] .. (main:28)ackerman_iter
[translation:ERROR] .. block@27 with 2 exits(v0)
[translation:ERROR] .. v2 = ne(v1, (None))

main.py

class AckermanNode(object):
	def __init__(self, n, next=None):
		self.n = n
		self.next = next
	def step(self):
		m = self.next.n 
		n = self.n
		node = self.next.next
		if m == 0:
			return AckermanNode(n + 1, node)
		elif m > 0 and n == 0:
			return AckermanNode(1, AckermanNode(m - 1, node))
		else:
			m_1 = m - 1
			for i in range(n):
				node = AckermanNode(m_1, node)
			return AckermanNode(0, AckermanNode(m, node))
		
def ackerman(m, n):
	if m == 0:
		return n + 1
	elif m > 0 and n == 0:
		return ackerman(m - 1, 1)
	else:
		return ackerman(m - 1, ackerman(m, n - 1))

def ackerman_iter(m, n):
	node = AckermanNode(n, AckermanNode(m))
	while node.next != None:
		node = node.step()
	return node.n

def ackerman_tuple(m, n, t):
	if m == 0:
		return (n + 1, t)
	elif m > 0 and n == 0:
		return (1, (m - 1, t))
	else:
		m_1 = m - 1
		for i in range(n):
			t = (m_1, t)
		return (0, (m, t))

def entry_point(argv):
	print ackerman_iter(int(argv[1]), int(argv[2]))
	return 0

def target(*args):
	return entry_point, None

if __name__ == "__main__":
    import sys
    entry_point(sys.argv)