/**
* Takes a RPN logical expression and evaluates it as true or false
*
* @static
* @param string $expr RPN expression
* @param array $vars variables lookup table
* @return bool evaluation
*/
public static function evaluate_rpn_expression($expr, $vars)
{
// Operators
$unary = array(SC_Survey_Flow::LO_NOT);
$binary = array(SC_Survey_Flow::LO_AND, SC_Survey_Flow::LO_OR);
//Split expression into tokens
$tokens = SC_Survey_Flow::tokenise($expr);
$tokens = array_map(function ($val) {
return str_replace(SC_Survey_Flow::LITERAL, '', $val);
}, $tokens);
//print_r($tokens);
$stack = [];
$loop = 1;
foreach ($tokens as $t) {
if (in_array($t, $unary)) {
//Token is a unary operator
$r = array_pop($stack);
$result = SC_Survey_Flow::evaluate_unary_logic($r, $t);
$stack[] = $result;
} elseif (in_array($t, $binary)) {
//Token is a binary operator
$r1 = array_pop($stack);
$r2 = array_pop($stack);
$result = SC_Survey_Flow::evaluate_binary_logic($r1, $r2, $t);
$stack[] = $result;
} else {
//Token is a condition
$result = SC_Survey_Flow::evaluate_condition($t, $vars);
//echo 'token: '.$t.' === '.($result ? 'TRUE' : 'FALSE').'<br />';
$stack[] = $result;
}
$loop++;
}
return $stack[0];
}
