[Cython] CF based type inference

[Stefan Behnel]

Vitja Makarov, 08.05.2012 15:47:
> 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.

How would type checks fit into this? Stupid example:

   def test(x):
       if isinstance(x, MyExtType):
           x.call_c_method()    # type known, no None check needed
       else:
           x.call_py_method()   # type unknown, may be None

Would it work to consider a type checking branch an assignment to a new
(and differently typed) entry?

Stefan