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Algorithm::Permute also includes some fun benchmarks comparing different
Perl ways of finding permutations.  I found NextPermute to be faster than
any of the routines included in those benchmarks except for the ones
written in C that I mentioned above.  Though none of the benchmarked
routines deal with duplicates.

=back

=head3 Notes

Note that NextPermute() considers two values (say $x and $y) to be
duplicates if (and only if) C<$x eq $y>.

NextPermuteNum() considers $x and $y to be duplicates if C<$x == $y>.

If you have a list of floating point numbers to permute, you might want
to use NextPermute() [instead of NextPermuteNum()] as it is easy to end
up with $x and $y that both display the same (say as "0.1") but are
B<just barely> not equal numerically.  Thus $x and $y would I<look> equal
and it would be true that C<$x eq $y> but also true that C<$x != $y>.  So
NextPermute() would consider them to be duplicates but NextPermuteNum()
would not.

For example, $x could be slightly more than 1/10, likely about
0.1000000000000000056, while $y is slightly more at about
0.0999999999999999917 (both of which will be displayed as "0.1" by Perl
and be considered C<eq> (on most platforms):