[Python-ideas] Cofunctions - an enhancement to yield-from

[ghazel at gmail.com]

On Sun, Aug 1, 2010 at 5:13 PM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
> ghazel at gmail.com wrote:
>
>> What I am suspicious of is automatically making calls to cofunctions
>> from within a cofunction imply 'yield from'. Knowing whether the
>> function call you are making can suspend your code and return to your
>> parent or not is important,
>
> The same situation occurs when dealing with threads, since any
> function you call could potentially suspend your thread. This
> doesn't seem to bother people much.

Exactly, it is the same situation as in threads, when it does not have
to be. If you can be preempted at any point, suddenly there is a need
for more fine-grained "locking" around state since you can not be sure
that some function will not pause your execution and allow something
further up the stack to modify it. With a special calling mechanism
these cooperative points are very clear, and you can write code to
handle potential state changes when the call returns. Instead of
locking around state, cooperative points are like unlocking for the
duration of the call.

>> I would like to
>> see a different calling mechanism when calling a cofunction,
>
> The main point of the whole thing is to avoid having to specially
> mark call sites like this. If you take that away, all that's left
> is the ability to define a generator without a yield, and I'm
> not sure it's worth having a whole new kind of function definition
> just for that.

Well, codef is the part I would like to see if anything is added at
all. Maybe that's not worth the trouble.

-Greg