private function evaluatePostfixNotation($tokens, $variables = array())
{
if ($tokens == false) {
return false;
}
$stack = new Stack();
foreach ($tokens as $token) {
if (in_array($token, array('+', '-', '*', '/', '^', '%'))) {
$lastOperatorTwo = $stack->pop();
$lastOperatorOne = $stack->pop();
if (is_null($lastOperatorOne)) {
return $this->raiseError('Internal error');
}
if (is_null($lastOperatorTwo)) {
return $this->raiseError('Internal error');
}
switch ($token) {
case '+':
$stack->push($this->executionEngine->add($lastOperatorOne, $lastOperatorTwo));
break;
case '-':
$stack->push($this->executionEngine->subtract($lastOperatorOne, $lastOperatorTwo));
break;
case '*':
$stack->push($this->executionEngine->multiply($lastOperatorOne, $lastOperatorTwo));
break;
case '/':
if ($lastOperatorTwo == 0) {
return $this->raiseError('Divide by zero error.');
}
$stack->push($this->executionEngine->divide($lastOperatorOne, $lastOperatorTwo));
break;
case '^':
$stack->push($this->executionEngine->pow($lastOperatorOne, $lastOperatorTwo));
break;
case '%':
$stack->push($this->executionEngine->mod($lastOperatorOne, $lastOperatorTwo));
break;
}
} elseif ($token == '_') {
// If the token is a unary operator, pop one value off the stack and
// then do the operation, then push it back on.
$stack->push(-1 * $stack->pop());
} elseif (preg_match("/^([a-z]\\w*)\\(\$/", $token, $matches)) {
// If the token is a function, pop arguments off the stack, hand them to
// the function and push the result back on.
$functionName = $matches[1];
if (in_array($functionName, $this->functions)) {
// The function name is one of the default functions.
$lastOperatorOne = $stack->pop();
if (is_null($lastOperatorOne)) {
return $this->raiseError('Internal error.');
}
// Handles the 'arc' trig synonyms.
$functionName = preg_replace("/^arc/", "a", $functionName);
// Converts 'ln' into the 'log' function name.
if ($functionName == 'ln') {
$functionName = 'log';
}
// Here the original code had an eval statement. We are going to try and do
// away with that and handle the function execution ourself. We will also do
// this so that this driver can use the MathExecutionEngine implementation.
// This piece of code will look-up a function on the MathExecutionEngine
// implementation and call an instance method on the implementation. We do this
// so that we do not have to define a use-case for each and every function
// that the driver may encounter.
if (in_array($functionName, $this->functions)) {
$stack->push($this->executionEngine->{$functionName}($lastOperatorOne));
}
} elseif (array_key_exists($functionName, $this->userFunctions)) {
// This is a user defined function.
$arguments = array();
for ($i = count($this->userFunctions[$functionName]['args']) - 1; $i >= 0; $i--) {
if (is_null($arguments[$this->userFunctions[$functionName]['args'][$i]] = $stack->pop())) {
return $this->raiseError('Internal error.');
}
}
$stack->push($this->evaluatePostfixNotation($this->userFunctions[$functionName]['func'], $arguments));
}
} else {
if (is_numeric($token)) {
$stack->push($token);
} elseif (array_key_exists($token, $this->constants)) {
$stack->push($this->constants[$token]);
} elseif (array_key_exists($token, $variables)) {
$stack->push($variables[$token]);
} else {
return $this->raiseError('Undefined variable \'' . $token . '\'');
}
}
}
// After there are no more tokens, the stack should have the final result.
if ($stack->getCount() != 1) {
return $this->raiseError('Internal error');
}
// Return the result.
return $stack->pop();
}
/**
* Calculates the factorial of a number.
*
* @param number $number
* @return number
*/
public function factorial($number)
{
return $this->executionEngine->factorial($number);
}