foo.go

func gen(nums ...int) <-chan int {
    out := make(chan int)
    go func() {
        for _, n := range nums {
            out <- n
        }
        close(out)
    }()
    return out
}

func sq(in <-chan int) <-chan int {
    out := make(chan int)
    go func() {
        for n := range in {
            out <- n * n
        }
        close(out)
    }()
    return out
}

func main() {
    // Set up the pipeline.
    c := gen(2, 3)
    out := sq(c)

    // Consume the output.
    fmt.Println(<-out) // 4
    fmt.Println(<-out) // 9
}

foo.pl6

sub gen(*@nums --> Supply) {
    my $source = Supplier::Preserving.new;
    start { $source.emit: $_ for @nums; $source.done }
    $source.Supply;
}

sub sq(Supply $in --> Supply) {
    supply whenever $in -> $n { emit $n * $n }
}

sub MAIN {
    my $c = gen(2, 3);
    my $out = sq($s);
    react whenever $out { .say }
}