case EXPR_MOD:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				if ( $right == 0 ) {
					throw new ExprError( 'division_by_zero', $this->names[$op] );
				}
				$stack[] = $left % $right;
				break;