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my $re = do {
    local $" = '|';
    qr/^@{[map {quotemeta} @list]}$/;
};

my @sets;
for (@list) {
    my $str = $_;
...
    }
}
my $re = qr/^${\join '', map {"[$_]"} @sets}$/;

{
    my %test_hash;
    @test_hash{@list} = ();
    sub efficient_test { exists $test_hash{+shift}; }
}