private void Ask(LinkedList<Expression> goals, KnowledgeBase context, Substitution theta, ProverCache cache, VariableRenamer renamer,
bool askOne, HashSet<Substitution> results, HashSet<Fact> alreadyAsking)
{
if (goals.Count == 0)
results.Add(theta);
else
{
Expression literal = goals.First.Value;
goals.RemoveFirst();
Expression qPrime = Substituter.Substitute(literal, theta);
var fact = qPrime as Fact;
if (fact != null && fact.RelationName == GameContainer.Parser.TokDistinct)
AskDistinct(fact, goals, context, theta, cache, renamer, askOne, results, alreadyAsking);
else
{
var negation = qPrime as Negation;
if (negation != null)
AskNot(negation, goals, context, theta, cache, renamer, askOne, results, alreadyAsking);
else
{
var disjunction = qPrime as Disjunction;
if (disjunction != null)
AskOr(disjunction, goals, context, theta, cache, renamer, askOne, results, alreadyAsking);
else
{
var sentence = (Fact) qPrime;
AskSentence(sentence, goals, context, theta, cache, renamer, askOne, results, alreadyAsking);
}
}
}
goals.AddFirst(literal);
}
}
private void AskDistinct(Fact distinct, LinkedList<Expression> goals, KnowledgeBase context, Substitution theta,
ProverCache cache, VariableRenamer renamer, bool askOne, HashSet<Substitution> results, HashSet<Fact> alreadyAsking)
{
if (!distinct.GetTerm(0).Equals(distinct.GetTerm(1)))
Ask(goals, context, theta, cache, renamer, askOne, results, alreadyAsking);
}
private void AskOr(Disjunction or, LinkedList<Expression> goals, KnowledgeBase context, Substitution theta,
ProverCache cache, VariableRenamer renamer, bool askOne, HashSet<Substitution> results, HashSet<Fact> alreadyAsking)
{
foreach (Expression expression in or.Constituents)
{
goals.AddFirst(expression);
Ask(goals, context, theta, cache, renamer, askOne, results, alreadyAsking);
goals.RemoveFirst();
if (askOne && (results.Any()))
break;
}
}
private void AskSentence(Fact sentence, LinkedList<Expression> goals, KnowledgeBase context, Substitution theta,
ProverCache cache, VariableRenamer renamer, bool askOne, HashSet<Substitution> results, HashSet<Fact> alreadyAsking)
{
if (!cache.Contains(sentence))
{
//Prevent infinite loops on certain recursive queries.
if(alreadyAsking.Contains(sentence)) {
return;
}
alreadyAsking.Add(sentence);
List<Implication> candidates = new List<Implication>();
candidates.AddRange(_knowledgeBase.Fetch(sentence));
candidates.AddRange(context.Fetch(sentence));
var sentenceResults = new HashSet<Substitution>();
foreach (Implication rule in candidates)
{
Implication r = renamer.Rename(rule);
Substitution thetaPrime = Unifier.Unify(r.Consequent, sentence);
if (thetaPrime != null)
{
LinkedList<Expression> sentenceGoals = new LinkedList<Expression>();
for (int i = 0; i < r.NumAntecedents(); i++)
sentenceGoals.AddLast(r.Antecedents.Constituents[i]);
Ask(sentenceGoals, context, theta.Compose(thetaPrime), cache, renamer, false, sentenceResults, alreadyAsking);
}
}
cache[sentence] = sentenceResults;
alreadyAsking.Remove(sentence);
}
foreach (Substitution thetaPrime in cache[sentence])
{
Ask(goals, context, theta.Compose(thetaPrime), cache, renamer, askOne, results, alreadyAsking);
if (askOne && (results.Any()))
break;
}
}
private void AskNot(Negation not, LinkedList<Expression> goals, KnowledgeBase context, Substitution theta, ProverCache cache,
VariableRenamer renamer, bool askOne, HashSet<Substitution> results, HashSet<Fact> alreadyAsking)
{
var notGoals = new LinkedList<Expression>();
notGoals.AddLast(not.Negated);
var notResults = new HashSet<Substitution>();
Ask(notGoals, context, theta, cache, renamer, true, notResults, alreadyAsking);
if (notResults.Count == 0)
Ask(goals, context, theta, cache, renamer, askOne, results, alreadyAsking);
}