[Cython] CF based type inference

[Vitja Makarov]

2012/5/9 Stefan Behnel <stefan_ml at behnel.de>:
> Robert Bradshaw, 09.05.2012 00:12:
>> On Tue, May 8, 2012 at 6:47 AM, Vitja Makarov wrote:
>>> 2012/5/8 Stefan Behnel:
>>>> Vitja has rebased the type inference on the control flow, so I wonder if
>>>> this will enable us to properly infer this:
>>>>
>>>>  def partial_validity():
>>>>    """
>>>>    >>> partial_validity()
>>>>    ('Python object', 'double', 'str object')
>>>>    """
>>>>    a = 1.0
>>>>    b = a + 2   # definitely double
>>>>    a = 'test'
>>>>    c = a + 'toast'  # definitely str
>>>>    return typeof(a), typeof(b), typeof(c)
>>>>
>>>> I think, what is mainly needed for this is that a NameNode with an
>>>> undeclared type should not report its own entry as dependency but that of
>>>> its own cf_assignments. Would this work?
>>>>
>>>> (Haven't got the time to try it out right now, so I'm dumping it here.)
>>>>
>>>
>>> Yeah, that might work. The other way to go is to split entries:
>>>
>>>  def partial_validity():
>>>   """
>>>   >>> partial_validity()
>>>   ('str object', 'double', 'str object')
>>>   """
>>>   a_1 = 1.0
>>>   b = a_1 + 2   # definitely double
>>>   a_2 = 'test'
>>>   c = a_2 + 'toast'  # definitely str
>>>   return typeof(a_2), typeof(b), typeof(c)
>>>
>>> And this should work better because it allows to infer a_1 as a double
>>> and a_2 as a string.
>>
>> This already works, right?
>
> It would work if it was implemented. *wink*
>
>
>> I agree it's nicer in general to split
>> things up, but not being able to optimize a loop variable because it
>> was used earlier or later in a different context is a disadvantage of
>> the current system.
>
> Absolutely. I was considering entry splitting more of a "soon, maybe not
> now" type of thing because it isn't entire clear to me what needs to be
> done. It may not even be all that hard to implement, but I think it's more
> than just a local change in the scope implementation because the current
> lookup_here() doesn't know what node is asking.
>

That could be done the following way:
 - Before running type inference find independent assignment groups
and split entries
 - Run type infrerence
 - Join entries of the same type or of PyObject base type
 - Then change names to private ones "{old_name}.{index}"

-- 
vitja.