my $input = join ' ', (1) x 1_001, ('+') x 1_000;

cmpthese(
    100,
    {
        recursive => sub { $input1 =~ $RPN1 },
        iterative => sub { $input2 =~ $RPN2 },
    },
);
            s/iter recursive      flat
recursive     1.35        --      -99%
iterative 1.47e-02     9103%        --