You might look at the existing art of
https://metacpan.org/pod/Future::Utils#REPEATING-A-BLOCK-OF-CODE which can
be used with Mojo::Promise via futurify/promisify, and seems a lot clearer
to me.
-Dan
On Tue, Oct 1, 2019 at 9:04 AM Roger Crew <c...@cs.stanford.edu> wrote:
> something I have found vaguely useful that I just uploaded to CPAN for
> people to play with
> Mojo::Promise::Role::Repeat,
>
> adds a *repeat()* method to the promise class/objects.
>
> The essential idea is that
>
> $promise->repeat(sub{...})
>
>
> is equivalent to
>
> $promise->then(sub{...})->then(sub{...})->then(sub{...})->then(sub{...}) #
> .... forever
>
>
> except that repeat() also returns a "final" promise, which is
>
> - rejected, if any iteration dies with a value or returns a promise
> that gets rejected
> - resolved with @values, if any iteration calls $_->(@values)
>
> and if any run of the handler sub{...} returns normally or with a promise
> that gets resolved, those values get fed to the next run,
>
> $_ being bound, at the start of each run, to an escape function that
> doesn't return -- the moral equivalent of a break statement -- *but *you
> can also use this function to break out of nested loops/handlers as well
> (though you'll need to stash it in a lexical if you're going to do that).
>
> The pattern that seems to be coming up a lot for me is
>
> $ua->get_p($first_url)->repeat(sub {
> # ... parse page ...
> $_->() if (victory);
> # ...
> $ua->get_p($next_url);
> })
>
>
> (I may eventually want to petition for some form of this to be added to
> Mojo::Promise, but one thing at a time...)
>
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