Hello, On Fri, Jan 24, 2003 at 05:48:42PM +0100, Samuele Pedroni wrote:
OTOH I think a higher level of abstraction is necessary to targert more general backends.
I agree with Samuele that we should not focus on ctypes or any other kind of structs right now. For all of ctypes' power I believe that it is not central to Python-in-Python. This will become important later, when we target C.
def binary_add(o1,o2): ...
(From my experience) a relevant issue is how to abstract over the PyTypeObject struct and the interpreter internal inheritance and lookup mechanisms (which do not correspond so directly to the language level semantics).
That's a point I would like to see discussed too. CPython has grown a quite complex set of routines to dispatch calls corresponding to the language operators. We could closely follow these algorithms, e.g. by translating PyNumber_Add() into a "number_add()" function testing the presence of the "nb_add" method on the arguments. This will be as messy as in CPython, but automatically gives exactly the same semantics. On the other hand, this dispatchers are heavily loaded with historical stuff and workarounds and could probably be better summarized in a higher-level implementation, taking into account the general direction that Python seems to evolve to. We could probably design something that still offers compatibility. For example, we might find out a general rule of multiple-dispatching that corresponds to what CPython conceptually does. In other words we could figure out a declarative way of saying which "nb_add" methods must be tried and in which order. Something that would find the set of all appliable "nb_add" methods, order them, and try them in that order until one of them succeeds. This is complicated by internal coercions (the nb_coerce method), which tend to disappear from Python. We will have to choose whether we keep it in the core, at the possible expense of conceptuality, or if we completely drop them from the core classes (and possibly re-implement them later, e.g. using wrapper classes around the so-called old-style-numbers classes). A bientôt, Armin.