/**
* Implementation of the shunting yard parsing algorithm
*
* @param array $tokens Token[] array of tokens to process
* @retval Node AST of the parsed expression
* @throws SyntaxErrorException
* @throws ParenthesisMismatchException
*/
private function shuntingYard(array $tokens)
{
// Clear the oepratorStack
$this->operatorStack = new Stack();
// Clear the operandStack.
$this->operandStack = new Stack();
// Remember the last token handled, this is done to recognize unary operators.
$lastNode = null;
// Loop over the tokens
for ($index = 0; $index < count($tokens); $index++) {
$token = $tokens[$index];
// echo "current token $token\n";
// echo("operands:" . $this->operandStack . "\n");
// echo("operators: " . $this->operatorStack . "\n\n");
if ($this->rationalFactory) {
$node = Node::rationalFactory($token);
} else {
$node = Node::factory($token);
}
// Handle closing parentheses
if ($token->getType() == TokenType::CloseParenthesis) {
$this->handleSubExpression();
} elseif ($node->isTerminal()) {
$this->operandStack->push($node);
// Push function applications or open parentheses `(` onto the operatorStack
} elseif ($node instanceof FunctionNode) {
$this->operatorStack->push($node);
} elseif ($node instanceof SubExpressionNode) {
$this->operatorStack->push($node);
// Handle the remaining operators.
} elseif ($node instanceof PostfixOperatorNode) {
$op = $this->operandStack->pop();
if ($op == NULL) {
throw new SyntaxErrorException();
}
$this->operandStack->push(new FunctionNode($node->getOperator(), $op));
} elseif ($node instanceof ExpressionNode) {
// Check for unary minus and unary plus.
$unary = $this->isUnary($node, $lastNode);
if ($unary) {
switch ($token->getType()) {
// Unary +, just ignore it
case TokenType::AdditionOperator:
$node = null;
break;
// Unary -, replace the token.
// Unary -, replace the token.
case TokenType::SubtractionOperator:
$node->setOperator('~');
break;
}
} else {
// Pop operators with higher priority
while ($node->lowerPrecedenceThan($this->operatorStack->peek())) {
$popped = $this->operatorStack->pop();
$popped = $this->handleExpression($popped);
$this->operandStack->push($popped);
}
}
if ($node) {
$this->operatorStack->push($node);
}
}
// Remember the current token (if it hasn't been nulled, for example being a unary +)
if ($node) {
$lastNode = $node;
}
}
// Pop remaining operators
while (!$this->operatorStack->isEmpty()) {
$node = $this->operatorStack->pop();
$node = $this->handleExpression($node);
$this->operandStack->push($node);
}
// Stack should be empty here
if ($this->operandStack->count() > 1) {
throw new SyntaxErrorException();
}
return $this->operandStack->pop();
}
