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Promise in Perl
Few days ago, I blogged about Future in Perl where I mentioned Future aka Promise.
In this post, I would replicate the behaviour using CPAN modules: Promise::ES6 and AE.
Since Perl believes in the philosophy of TMTOWTDI, so let’s implement the most basic pattern of Promiseas below:
fetch()
.then(process)
.then(save)
.then(display)
.catch(error);
#!/usr/bin/env perl
use v5.38;
use AE;
use Promise::ES6;
my $ae = AE::cv;
sub fetch {
return Promise::ES6->new(sub {
my ($resolve, $reject) = @_;
my $delay = int(rand(2)) + 1;
my $timer;
$timer = AE::timer $delay, 0, sub {
undef $timer;
$resolve->("Fetch: data");
};
});
}
sub process($data) {
return Promise::ES6->new(sub {
my ($resolve, $reject) = @_;
my $delay = int(rand(2)) + 1;
my $timer;
$timer = AE::timer $delay, 0, sub {
undef $timer;
$resolve->("Process: $data");
};
});
}
sub save($data) {
return Promise::ES6->new(sub {
my ($resolve, $reject) = @_;
my $delay = int(rand(2)) + 1;
my $timer;
$timer = AE::timer $delay, 0, sub {
undef $timer;
$resolve->("Save: $data");
};
});
}
sub display($data) {
say "Display: $data";
$ae->send;
}
sub error($message) {
say "Error: $message";
$ae->send;
}
fetch()
->then( sub { return process(@_); })
->then( sub { return save(@_); })
->then( sub { return display(@_); })
->catch(sub { return error(@_); });
$ae->recv;
Output
$ perl promise.pl
Display: Save: Process: Fetch: data
Happy Hacking!!