Raku Books / Perl 6 at a Glance / New Concepts / Promises

anyof and allof

Another pair of factory methods, Promise.anyof and Promise.allof, creates new promises, which will be only kept when at least one of the promises (in the case of anyof) is kept or, in the case of allof, all of the promises listed at the moment of creation are kept.

One of the useful examples found in the documentation is a timeout keeper to prevent long calculations from hanging the programme.

Create the promise $timeout, which must be kept after a few seconds, and the code block, which will be running for longer time. Then, list them both in the constructor of Promise.anyof.

my $code = start {
    sleep 5
}
my $timeout = Promise.in(3);

my $done = Promise.anyof($code, $timeout);
say $done.result;

🧵 This program uses concurrency (promises, threads). The in-browser engine (Raku.js) is single-threaded and can’t run it yet — try it on your own computer.

CodeBlockPlaceholder2raku-async my $p = Promise.in(2); my $t = $p.then({say “OK”}); # Prints this in two seconds

say “promised”; # Prints immediately sleep 3;

say “done”; CodeBlockPlaceholder3

promised OK done CodeBlockPlaceholder4

In another example, the promise is broken.

Promise.start({  # A new promise
    say 1 / 0    # generates an exception
                 # (the result of the division is used in say).
}).then({        # The code executed after the broken line.
    say "oops"
}).result        # This is required so that we wait until
                 # the result is known.

🧵 This program uses concurrency (promises, threads). The in-browser engine (Raku.js) is single-threaded and can’t run it yet — try it on your own computer.

The only output here is the following:

oops

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