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);