$str = '( (1 == 1) and (2 < 1) ) or (2 > 0)';
  while ($str =~ s/(\([^()]+\))/$1/ee) {
    if (not eval($1)) {
       print "error: $1\n"; 
       last;
    }
  }

##</code><code>##

  $str = '( (1 == 1) and (2 < 1) ) or (2 > 0)';
  while ($str =~ s/(\([^()]+\))/qq($1 || 0)/ee) {
       print eval($1) ? 'ok' : 'error';
       print ": $1\n";
  }

##</code><code>##

ok: (1 == 1)
error: (2 < 1)
error: ( 1 and 0 )
ok: (2 > 0)

##</code><code>##

  $str = '( (1 == 1) or (2 < 1) ) and (2 > 0)';