Course of Raku / Functional, concurrent, reactive, and web programming / Concurrent programming / Channels / Exercises / Sum a channel

Solution: Sum a channel

Here is a possible solution to the task.

Code

my $c = Channel.new;

my $producer = start {
    $c.send($_) for 1..6;
    $c.close;
};

my $consumer = start {
    [+] $c.list;
};

my ($sent, $sum) = await $producer, $consumer;
say $sum;

🦋 You can find the source code in the file channel-sum.raku.

Output

21

Comments

1. The producer promise sends the six values on one thread and closes the channel. The consumer promise, on another thread, uses .list to collect everything up to the close and returns the sum ([+] adds 1 + 2 + … + 6).

2. await $producer, $consumer waits for both promises and returns their results in order. The producer’s result is not needed here ($sent); the consumer’s is the sum, 21. The channel is what safely carries the values from the producer thread to the consumer thread.

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