private function step(&$tokenStream, Symbol $symbol, &$parseTreeBranch)
{
$returnValue = false;
$this->depth++;
$alternatives = $symbol->getConsistence();
$altChangedSth = false;
//iterating over alternatives
foreach ($alternatives as $alt) {
//iterating over symbols and terminals an alternative consists of
$alternativeMatched = true;
$first = true;
foreach ($alt as $parseElement) {
if ($this->debug) {
$this->debugOutput(str_repeat(" ", $this->depth) . $this->depth . " " . $parseElement->getName() . " " . get_class($parseElement));
}
if (is_a($parseElement, "Terminal")) {
if ($parseElement->getName() == "V_e") {
//alternative consists of epsilon, so alternative has matched, because alternative and therefore symbol has fullfilled it's destination
$alternativeMatched = true;
break;
} else {
if (count($tokenStream) == 0) {
if ($first) {
//having no more tokens, i say this alternative failes.but it's the first token to check, so let's see if epsilon is produced in another alternative
$alternativeMatched = false;
break;
} else {
//uh, I'm in the middle of something? breaking baaaaad.
throw new ParserException("I'm through with the Input-Band, i was expecting: " . $parseElement->getName() . ", not good!");
}
}
//peek on tokenstream, $tokenStream[0] matches terminal->name?
if ($parseElement->getName() == $tokenStream[0]['symbol']) {
if ($this->debug) {
$this->debugOutput(str_repeat(" ", $this->depth) . " FOUND! | " . $this->listTokenString($tokenStream));
}
//shift it out
$parseTreeBranch[] = array_shift($tokenStream);
} else {
if ($this->debug) {
$this->debugOutput(str_repeat(" ", $this->depth) . " not found! | " . $this->listTokenString($tokenStream));
}
//hmm, is first?
if ($first) {
//let's try another alternative
$alternativeMatched = false;
break;
} else {
//i ran in this one...not return, breaking bad
throw new ParserException("Unexpected Token: " . $tokenStream[0]['symbol'] . ", Expected: " . $parseElement->getName());
}
}
}
} else {
if (is_a($parseElement, "Symbol")) {
//get symbol and pass it to new cycle of functioni
$mySymbol = $this->symbols[$parseElement->getName()];
$tmpParseTreeBranch = array();
$retVal = $this->step($tokenStream, $mySymbol, $tmpParseTreeBranch);
//got a symbol match or not? if yes, break alternative and switch to next one
if (!$retVal) {
if ($first) {
$alternativeMatched = false;
break;
} else {
//i ran in this one...not return, breaking bad
throw new ParserException("Expected: " . $parseElement->getName());
}
} else {
$parseTreeBranch[$parseElement->getName()] = $tmpParseTreeBranch;
}
}
}
$first = false;
}
if ($alternativeMatched) {
//current alternative produced a complete match. no need to check other alternatives
$returnValue = true;
break;
}
}
$this->depth--;
return $returnValue;
}
