If you initialize %STR_OPS and %NUM_OPS as follows:

# Do this once for efficiency.
use vars qw(%NUM_OPS %STR_OPS);
BEGIN {
   $NUM_OPS{$_} = eval "sub { \$_[0] $_ \$_[1] }"
      foreach (qw(<  <= != >= >  ==));

   $STR_OPS{$_} = eval "sub { \$_[0] $_ \$_[1] }"
      foreach (qw(lt le ne ge gt eq));
}
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Then the snippet boils down to:

            $v = ${$pairs{$ca}}[0];
            if ($types{$ca}) {
                $v = 0 unless defined $v;
                $op = $NUM_OPS{$co};
            } else {
                $v = '' unless defined $v;
                $op = $STR_OPS{$co};
            }
            die("Undefined operation $co.\n") unless $op;
            $r &= $op->($v, $cv);
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It's even more robust than the original.

I would go further, and make a single array or hash containing all of %NUM_OPS and %STR_OPS. For example:

BEGIN {
   $OPS{'num'}{$_} = eval "sub { \$_[0] $_ \$_[1] }"
      foreach (qw(<  <= != >= >  ==));

   $OPS{'str'}{$_} = eval "sub { \$_[0] $_ \$_[1] }"
      foreach (qw(lt le ne ge gt eq));
}

# ... and later ...

$v = ${$pairs{$ca}}[0];
my $op_type = $types{$ca} ? 'num' : 'str';
my $op = $OPS{$op_type}{$co};
die("Undefined operation $co.\n") unless $op;
$r &= $op->($v, $cv);
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It would be even better if you could alter the code which sets up %types, so that instead of true and false values, it could store the strings we need: 'num' or 'str'.

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