Python: Parsing a simple grammar with parcon

Question

I'm trying to use parcon to parse a simple grammar for boolean-valued statements and expressions that look like this:

foo = True
bar = foo or False

Here's the grammar definition I'm trying:

from parcon import (
    Word,
    Literal,
    SignificantLiteral,
    Forward,
    Return,
    alpha_chars,
)

m_boolean = Literal("True")[lambda x: True] | Literal("False")[lambda x: False]

m_and = SignificantLiteral('and')(name='AND')
m_or = SignificantLiteral('or')(name='OR')

m_logical_operator = m_and | m_or

m_identifier = (Word(alpha_chars) - m_logical_operator)

m_expression = Forward()

m_subexpression = '(' + m_expression + ')'

m_term = m_boolean | m_identifier | m_subexpression

m_expression_tail= Forward()
m_infix_expression = m_term + m_expression_tail
m_expression_tail << (
    (m_logical_operator + m_expression + m_expression_tail)
    |
    (Return(None))
)

m_expression << (m_term | m_infix_expression)

def test(toker, tests):
    print '\n'

    l = [x.strip() for x in tests.split('\n') if x.strip() != '']
    for test in l:
        print test, ':',
        print toker.parse_string(test)

test(m_subexpression, '''
(True)
(foo)
''')
test(m_term, '''
True
foo
(True)
''')
test(m_infix_expression, '''
a and b
True and False
''')
test(m_expression, '''
True
( True )
True and False
a and b
not True
not a
True or (b)
a and (False)
foo
(foo)
(a or b) and (c or d)
''')

It works for some of my tests, but I'm getting this error when parsing m_expression:

True and False :
Traceback (most recent call last):
  File "boolean_parcon.py", line 78, in <module>
    ''')
  File "boolean_parcon.py", line 18, in test
    print toker.parse_string(test)
  File "/usr/local/lib/python2.7/dist-packages/parcon/__init__.py", line 620, in parse_string
    self, getattr(self,'name',''), format_failure(result.expected)))
parcon.ParseException: Parse (Forward() ) failure: At position 4: expected one of EOF 

I don't understand why. I think I've eliminated any possibility of infinite left recursion. The error seems to indicate that True and False is being parsed by the m_term rule and giving up. I would have thought after failing m_term, it would next attempt m_infix_expression. Any pointers?

Alternatively, could anyone recommend a grammar definition tool that might work better for me than parcon?