/// <summary>
/// Searches the description for statements that are needlessly treated as base propositions when they could be
/// expressed as simple relations, and replaces them with these simpler forms.
///
/// Some games have been written such that unchanging facts of the game are listed as base propositions. Often, this
/// is so the fact can be accessed by a visualization. Gamers usually don't need this distinction, and can reduce
/// the costs in time and memory of processing the game if these statements are instead transformed into sentences.
/// </summary>
/// <param name="description"></param>
/// <returns></returns>
public static List<Expression> Run(IList<Expression> description)
{
ImmutableSentenceFormModel model = SentenceFormModelFactory.Create(description);
int next = GameContainer.Parser.TokNext;
var nextFormsToReplace = new List<ISentenceForm>();
IEnumerable<ISentenceForm> nextForms = model.SentenceForms.Where(m => m.Name.Equals(next));
//Find the update rules for each "true" statement
foreach (ISentenceForm nextForm in nextForms)
{
//See if there is exactly one update rule, and it is the persistence rule
ISet<Implication> updateRules = model.GetRules(nextForm);
if (updateRules.Count == 1)
{
Implication updateRule = updateRules.First();
//Persistence rule: Exactly one literal, the "true" form of the sentence
if (updateRule.Antecedents.Constituents.Length == 1)
{
Expression literal = updateRule.Antecedents.Constituents[0];
var body = literal as Fact;
if (body!=null)
{
//Check that it really is the true form
ISentenceForm trueForm = nextForm.WithName(GameContainer.Parser.TokTrue);
if (trueForm.Matches(body))
{
Fact head = updateRule.Consequent;
//Check that the tuples are the same, and that they consist of distinct variables
List<Term> headTuple = head.NestedTerms.ToList();
List<Term> bodyTuple = body.NestedTerms.ToList();
if (headTuple.Equals(bodyTuple) && headTuple.Distinct().Count() == headTuple.Count)
nextFormsToReplace.Add(nextForm);
}
}
}
}
}
var newDescription = new List<Expression>(description);
//Now, replace the next forms
foreach (ISentenceForm nextForm in nextFormsToReplace)
{
ISentenceForm initForm = nextForm.WithName(GameContainer.Parser.TokInit);
ISentenceForm trueForm = nextForm.WithName(GameContainer.Parser.TokTrue);
//Go through the rules and relations, making replacements as needed
for (int i = 0; i < newDescription.Count; i++)
{
Expression gdl = newDescription[i];
var relation = gdl as Fact;
if (relation != null)
{
//Replace initForm
if (initForm.Matches(relation))
{
var terms = relation.GetTerms();
var function = terms[0] as TermFunction;
Debug.Assert(function != null);
newDescription[i] = new VariableFact(true, function.FunctionName, function.Arguments);
}
}
else if (gdl is Implication)
{
var rule = (Implication)gdl;
//Remove persistence rule (i.e. rule with next form as head)
Fact head = rule.Consequent;
if (nextForm.Matches(head))
newDescription.RemoveAt(i--);
else
{
//Replace true in bodies of rules with relation-only form
List<Expression> body = rule.Antecedents.Constituents.ToList();
List<Expression> newBody = ReplaceRelationInBody(body, trueForm);
if (!body.Equals(newBody))
newDescription[i] = new Implication(head, newBody.ToArray());
}
}
}
}
return newDescription;
}
public VariableFact ProcessFact(VariableFact fact)
{
return fact.Clone(_relName);
}
private static Fact SubstituteSentence(Fact sentence, Substitution theta)
{
if (sentence is GroundFact)
return sentence;
var body = new List<Term>();
for (int i = 0; i < sentence.Arity; i++)
body.Add(SubstituteTerm(sentence.GetTerm(i), theta));
var variableFact = new VariableFact(false, sentence.RelationName, body.ToArray());
return variableFact.VariablesOrEmpty.Any()
? variableFact
: (Fact) new GroundFact(sentence.RelationName, body.ToArray());
}