The pipe filter also uses reduce?

The idea that comes to my mind is a sliding window , like @ten, so before your program reduce

ahoy(\@points);

sub ahoy {
    my( $points ) = @_;
    my @ten;
    for my $point ( @$points ){
        push @ten, $point;
        if( @ten > 1    and     $ten[-1][0] < $ten[-2][0]   ){ ## back
+ing up? ditch it
            splice @ten, -2; ## pop pop @ten;
        }
        
        if( @ten > 9 ){
            print join ' ', @$_ for splice @ten, 0, 8 ; ## shift 8
        }
    }
    print join ' ', @$_ for @ten;
    print '####';
}
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