mutual left recursion not supported

[rbtcollins]

The OMeta paper describes mutual left recursion as a supported feature, but it appears broken in parsley.

Consider a simple left recursive grammar (this works):

exp = """\
num = <digit+>:n -> int(n)
expr = expr:e "-" num:n -> e - n
     | num
"""
compiled = makeGrammar(exp, {})
print(compiled("4-3").expr())

->

1

Now lets modify the grammar precisely as done in the paper: replacing expr in the expr recursion with another rule x that calls into expr:

exp = """\
num = <digit+>:n -> int(n)
x = expr
expr = x:e "-" num:n -> e - n
     | num
"""
compiled = makeGrammar(exp, {})
print(compiled("4-3").x())

->

Traceback (most recent call last):
  File "./t.py", line 36, in <module>
    print(compiled("4-3").x())
  File "/home/robertc/.virtualenvs/scratch/local/lib/python2.7/site-packages/parsley.py", line 98, in invokeRule
    raise err
ometa.runtime.ParseError: 
4-3
  ^
Parse error at line 1, column 2: expected EOF. trail: [digit]

If run with expr rather than x, the result is the same.