Re: On raw strings in <origin> commit field

[Liliana Marie Prikler]

Hi,

Am Donnerstag, dem 06.01.2022 um 05:38 -0500 schrieb Mark H Weaver:
> > From here on, I will assume that each individual push action is
> > finite as you did, but I don't think that using communications of
> > finite length are a helpful building block here.
> 
> Really?  You don't think communications of finite length are a
> helpful building block here?
> 
> Note that in the real world, every observable time interval is
> finite.
The reason I don't is because if we go all the way back to what we
actually want to do, we're invoking claims of an uncertain future.  At
the time of pushing a package description to guix.git, we already ran
whatever tests we had for the upstream and determined what we believe
to be a safe course of actions.  In theory, this belief could be
shattered mere seconds after.

> You referred to "Git" here.  That's why my proof was about Git.  You
> didn't say that you were talking about some theoretical variant of
> Git that supports "push actions" that literally *never* end, and that
> runs on a theoretical machine with infinite memory that can never be
> built.
Now to be sure, we're both talking about Git here, the porting to
Turing machines is only relevant because if we go that deep to Computer
Science basics, we might as well use them.
The scary parts of Git, that we use to make robustness claims are:
1. In the future, upstream might delete the repo.
2. In the future, upstream might update or delete a branch.
3. In the future, upstream might update or delete a tag.
4. In the future, upstream might update or delete a commit.
> 

> No, that's incorrect.  The set of lists of booleans is countable.
> Moreover, for any type T, if the set of objects of type T is
> countable, then the set of _lists_ of objects of type T is also
> countable.

> Note that lists are finite, by definition.
I'm pretty sure that there's bounded and unbounded lists, but perhaps I
am confusing the latter for infinite streams as you've pointed out.  

> If you intend to claim that by "push actions", you meant to include
> infinite streams of push actions: this has no relevance to the real
> world.
> 
> Even if we live in an open universe, the fact remains that at any
> arbitrary point in time, the age of any git repository is always
> finite.  Therefore, no one can ever observe the result of an
> infinite-length "push action" in the real world.  They can only ever
> observe the result of some finite prefix of that so-called "push
> action".
Even in a closed universe, we can only jump to arbitrary points in time
of which we've already collected a snapshots.  Statements regarding
anything else always carry uncertainty.

That's also a reason to bring Turing machines into this equation.  A
Turing machine would try to observe an infinite stream of push actions
if we program it that way.  This raises the Halting and Non-Halting
problems among others.

Cheers