Here's the other Gleam concurrency example in Raku for good measure:

  my @promises;

  sub MAIN() {
    # Run loads of green threads, no problem
    for ^200_000 {
      spawn-greeter($++);
    }

    await Promise.allof(@promises);
  }

  sub spawn-greeter($i) {
    @promises.push: start {
      say "Hello from $i";
    }
  }