Bah, if you have to use a hash anyway, eval doesn't help any.

my %perlop = (
   lte => sub { $_[0] <= $_[1] },
   gte => sub { $_[0] >= $_[1] },
   # ...
);

my $r = $perlop{$op}->($a, $b);
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(Oops, seems I had the page opened a while without realising it, and others have already answered this since then.)