/// <summary>
/// Returns a symmetrical input boolean fact.
/// For example, A is married to B if B is married to A.
/// </summary>
/// <remarks>
/// See unit tests for the truth table, which ensures that the existence
/// of one false causes a false to be returned.
/// Note that the Sym() functions are also designed to add facts to the
/// Facts.Unknowns list in the proper order and with proper short-
/// circuiting.
/// </remarks>
public static Tbool Sym(object subj, string rel, object directObj)
{
if (Facts.HasBeenAsserted(rel, subj, directObj))
{
return(QueryTvar <Tbool>(rel, subj, directObj));
}
return(QueryTvar <Tbool>(rel, directObj, subj));
}
/// <summary>
/// Determines whether the rule should short-circuit before firing the actual rule logic.
/// </summary>
public static RulePreCheckResponse ShortCircuitValue <T>(string rel, string symIndicator, string questionIndicator, params object[] argList) where T : Tvar
{
// First, determine whether any of the Things are unknown.
Hstate h = EntityArgIsUnknown(argList);
if (h != Hstate.Known)
{
T scv = (T)Util.ReturnProperTvar <T>(new Hval(null, h));
return(new RulePreCheckResponse(scv, true));
}
// Extract argument parameters from argList
object param1 = argList[0];
object param2 = argList.Length > 1 ? argList[1] : null;
object param3 = argList.Length > 2 ? argList[2] : null;
// Adds the function node to the proof tree
Engine.AddToProofTree(new Facts.Fact(rel, param1, param2, param3, "?"));
// Handle symmetrical facts
if (symIndicator == "Sym")
{
// If the fact has not been asserted, add it to the list of unknown facts, so it gets asked.
if (!Facts.HasBeenAssertedSym(param1, rel, param2))
{
// EXPERIMENTAL: First, ask any assumed facts
if (Facts.GetUnknowns)
{
// if (Facts.Sym(param1, rel, param2).IsEternallyUncertain)
// {
// Assumptions.AskAssumedFacts(rel, param1, param2, param3);
// Assumptions.AskAssumedFacts(rel, param2, param1, param3);
// }
// "?" indicates that this node is a question to be asked of the user
if (questionIndicator == "?")
{
Facts.AddUnknown(rel, param1, param2, null);
}
}
}
// If the fact has been asserted and is not "uncertain", return the asserted value.
else
{
Tbool f = Facts.Sym(param1, rel, param2);
if (!f.IsEternallyUncertain)
{
return(new RulePreCheckResponse(f, true));
}
}
}
// Handle non-symmetrical facts (same code pattern as above)
else
{
if (!Facts.HasBeenAsserted(rel, param1, param2, param3))
{
if (Facts.GetUnknowns)
{
// EXPERIMENTAL: First, ask any assumed facts
// Assumptions.AskAssumedFacts(rel, param1, param2, param3, false);
if (questionIndicator == "?")
{
Facts.AddUnknown(rel, param1, param2, param3);
}
}
}
else
{
T f = Facts.QueryTvar <T>(rel, param1, param2, param3);
if (!f.IsEternallyUncertain)
{
return(new RulePreCheckResponse(f, true));
}
}
}
// Otherwise, proceed to examine the rule conditions and sub-rules.
return(new RulePreCheckResponse(null, false));
}
