static function eval_expression($args, $context)
{
$op_stack = array();
$num_stack = array();
$expression_pos = 0;
// Tracks position in the expression for better error reporting.
$back_track_pos = 0;
// Tracks position in the expression when backtracking for better error reporting.
foreach ($args as $arg) {
$expression_pos++;
if (is_array($arg) && isset($arg['operator'])) {
$back_track_pos = $expression_pos;
while (Evaluator::higher_op_on_stack($arg['operator'], $op_stack)) {
$val = Evaluator::eval_op_stack($op_stack, $num_stack, $back_track_pos);
$num_stack[] = $val;
}
$op_stack[] = $arg['operator'];
} else {
if (is_array($arg) && isset($arg['parentheses'])) {
if ($arg['parentheses'] === '(') {
$op_stack[] = '(';
} else {
$back_track_pos = $expression_pos;
while ($op = array_pop($op_stack)) {
if ($op === '(') {
break;
}
$op_stack[] = $op;
$num_stack[] = Evaluator::eval_op_stack($op_stack, $num_stack, $back_track_pos);
}
if (is_null($op)) {
throw new Exception("No opening paren for ')' at {$expression_pos}");
}
}
} else {
$num_stack[] = $context->resolve($arg);
}
}
}
$back_track_pos = $expression_pos;
while (count($op_stack) > 0) {
$num_stack[] = Evaluator::eval_op_stack($op_stack, $num_stack, $back_track_pos);
}
return array_pop($num_stack);
}
