This is how you could define a "hash subtraction" operator, i.e. an operator that returns the set difference between two hashes: 
multi sub infix:<-> (%main, %dict)  {
    my %difference;
    for %main.keys -> $word            {
         %difference{$word}  =  1  unless %dict{$word}:exists;
    }
    return %difference;
}

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You can now use the minus operator too compute the set differences between the two hashes.

Update: I did not have time to complete when I wrote the above.

Now, assuming you have a %book-words hash containing all the different words in a given book, and a %dictionary hash, you could build a hash with all the words in the book and not in the dictionary: 

my %missing-words = %book-words - %dictionary;

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Perl 6 does not define the minus operator between hashes, but it can easily be added to the language as shown above, and Perl 6 won't get confused.

In reply to Re: [Perl6] Can i put a operator in container (Perl 6) by Laurent_R
in thread [Perl6] Can i put a operator in container by freakcoco

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