Recursive deferred promises: sometimes you need to run a set of actions consecutively without knowing how many actions exist. An example would be running an arbitrary number of commands one after the other. You want to be able to add more commands to the array without having to add another explicit deferred promise. This code shows how to recurs…

recur_def_promise.pl

use strict;
use warnings;
use AnyEvent;
use AnyEvent::HTTP;
use Promises 'deferred';

my @urls = ( 'https://ddg.gg', 'http://dyndns.org', 'http://metacpan.org' );
my $cv   = AE::cv;

my $cb; $cb = sub {
    my $url = shift @urls or return $cv->send;
    my $def = deferred;

    http_get $url, sub { $def->resolve };
    $def->promise->then($cb);
};

# first call
my $def = deferred;
http_get shift(@urls), sub { $def->resolve };
$def->promise->then($cb);

$cv->recv;