That's not very efficient. You go into recursion twice, resulting in an exponential amount of subroutine calls. For n = 10, you call gen_seqs 1024 times. The following snippet calls gen_seqs only n + 1 times, while dealing with n = 0 correctly:

    sub gen_seqs;
    sub gen_seqs {
        return [] if $_ [0] <= 0;
        my @s = gen_seqs $_ [0] - 1;
       (map {[0 => @$_]} @s), (map {[1 => @$_]} @s)
    }
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Abigail