private function eval_term(Term $term)
{
$rel = $term->getName();
$vars = $term->getVariables();
// $vars: [Variable]
// all variables have value, no need to generate/iterate candidates
if ($term->readyForResolve()) {
return $this->isTrue($rel, $term->getInstances());
}
/* ---------Have to fill the variables with a candidate value ----------- */
try {
if ($this->isRule($rel)) {
$candidates = $this->instance_generator_for_rule($term);
} else {
$candidates = $this->instance_generator_for_fact($term);
}
} catch (Exception $e) {
//echo "no candidates for: \n"; echo " " . $term->toString() . "\n";
return FALSE;
}
foreach ($candidates as $_instances) {
//echo $term->toString() . "\n";
//print_r($_instances);
$term->assignValues($_instances);
// if $term is fact, isTrue() will not assign value for
// variables, it could make wrong variable value for next
// term. for example:
// hasDesc(A, C) :- hasChild(A, B) o hasDesc(A, C)
// assign A = 'x', C = 'z'
// hasDesc('x', 'z') :- hasChild('x', ?) o hasDesc(?, 'z')
// assign ? = 'y'
// hasDesc('x', 'z') :- hasChild('x', 'y') o hasDesc('y', 'z')
// if we don't assigin value to ?
// hasDesc(?, 'z') will be evaulated
// the candicate of ? could be ['x', 'y', 'z'], then
// hasDesc('x', 'z') cause infinite loop
if ($this->isTrue($rel, $_instances)) {
// recursive eval next, if return true, return true
// if next term false, continue the iteration
if (NULL == $term->next()) {
return TRUE;
}
// no more for eval
if ($this->eval_term($term->next())) {
return TRUE;
}
}
}
return FALSE;
// all candidate are false.
}
