Just out of curiosity, I know there's still a lot up in the air (err?), but won't this be a syntax error?
You have an @ to designate "seen" as an array (Perl6 terminology, folks!, I know that's not correct for Perl5), but you're using the curlies for a hash. I am assuming that what you meant to do was use a hash slice of elements in @data and set all elements to 1 (true). If so, I believe that would be:
For those not familiar with Perl 6 idioms, that would be the equivalent of the following in Perl 5:
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In reply to (Ovid) Re(2): Thoughts on Perl6 - Love it? Hate it?