function __construct($expression = '')
{
$this->expression = str_replace(' ', '', $expression);
preg_match_all('%(?:(?P<dice>' . DICE_REGEX . ')|(?P<set>\\d*\\[[^\\]]+\\])|(?P<numeral>[\\d\\.]+)|(?P<operator>[+\\-*^><=/])|(?P<variable>\\$[a-z_]+)|(?P<parens>[()]))%i', $this->expression, $matches, PREG_SET_ORDER);
$stack = array();
foreach ($matches as $match) {
$match = array_filter($match);
if (isset($match['numeral'])) {
$this->rpn[] = $match['numeral'];
$this->infix[] = $match['numeral'];
} elseif (isset($match['dice'])) {
$dice = new CalcDice($match['dice']);
$this->rpn[] = $dice->value();
$this->infix[] = $dice;
} elseif (isset($match['set'])) {
$this->rpn[] = new CalcSet($match['set']);
$this->infix[] = end($this->rpn);
} elseif (isset($match['operator'])) {
while (count($stack) > 0 && end($stack) != '(' && $this->ooo[$match['operator']] <= $this->ooo[end($stack)]) {
$this->rpn[] = array_pop($stack);
}
$stack[] = $match['operator'];
$this->infix[] = $match['operator'];
} elseif (isset($match['variable'])) {
$this->rpn[] = $match['variable'];
$this->infix[] = end($this->rpn);
} elseif (isset($match['parens'])) {
$this->infix[] = $match['parens'];
if ($match['parens'] == '(') {
$stack[] = $match['parens'];
} else {
while (count($stack) > 0 && end($stack) != '(') {
$this->rpn[] = array_pop($stack);
}
array_pop($stack);
}
} else {
$stack = array('Invalid token:', $match);
break;
}
}
while (count($stack) > 0) {
$this->rpn[] = array_pop($stack);
}
}
protected function match_dice($dice) {
$dice = new CalcDice($dice);
$this->rpn[] = $dice->value();
$this->infix[] = $dice;
}