/// <summary>
/// Generates all possible PDDL relative states meeting given CNF conditions (in the form of a list of conjuncts). Lazy generated recursively via yield return.
/// </summary>
/// <param name="index">Current index in the conjuncts list.</param>
/// <param name="conjuncts">List of conjuncts of the CNF conditions.</param>
/// <param name="result">Current relative state being built.</param>
/// <returns>All possible PDDL relative states meeting the CNF conditions.</returns>
private static IEnumerable <IRelativeState> EnumerateRelativeStatesByCNF(int index, List <IConjunctCNF> conjuncts, IRelativeState result)
{
if (index == 0)
{
// the constructed state can have trailing values from the previous unfinished enumeration!
result.ClearContent();
}
Action <IRelativeState, LiteralCNF> addLiteral = (state, literal) =>
{
// Note: At the moment, there is limited support for object and numeric function assignments.
// For example, numeric comparison literals like (< (numFunc) 5) will be omitted in the resulting relative state.
PredicateLiteralCNF predicateLiteral = literal as PredicateLiteralCNF;
if (predicateLiteral != null)
{
if (literal.IsNegated)
{
state.AddNegatedPredicate(predicateLiteral.PredicateAtom.Clone());
}
else
{
state.AddPredicate(predicateLiteral.PredicateAtom.Clone());
}
return;
}
EqualsLiteralCNF equalsLiteral = literal as EqualsLiteralCNF;
if (equalsLiteral != null)
{
var assignment = equalsLiteral.TryGetObjectFunctionAssignment();
if (assignment != null)
{
if (!literal.IsNegated)
{
state.AssignObjectFunction(assignment.Item1.FunctionAtom.Clone(), assignment.Item2.NameId);
}
}
return;
}
NumericCompareLiteralCNF compareLiteral = literal as NumericCompareLiteralCNF;
if (compareLiteral != null)
{
var assignment = compareLiteral.TryGetNumericFunctionAssignment();
if (assignment != null)
{
if (!compareLiteral.IsNegated)
{
state.AssignNumericFunction(assignment.Item1.FunctionAtom.Clone(), assignment.Item2.Value);
}
}
}
};
Action <IRelativeState, LiteralCNF> removeLiteral = (state, literal) =>
{
PredicateLiteralCNF predicateLiteral = literal as PredicateLiteralCNF;
if (predicateLiteral != null)
{
if (literal.IsNegated)
{
state.RemoveNegatedPredicate(predicateLiteral.PredicateAtom.Clone());
}
else
{
state.RemovePredicate(predicateLiteral.PredicateAtom.Clone());
}
return;
}
EqualsLiteralCNF equalsLiteral = literal as EqualsLiteralCNF;
if (equalsLiteral != null)
{
var assignment = equalsLiteral.TryGetObjectFunctionAssignment();
if (assignment != null)
{
if (!literal.IsNegated)
{
state.AssignObjectFunction(assignment.Item1.FunctionAtom.Clone(), ObjectFunctionTerm.UndefinedValue);
}
}
return;
}
NumericCompareLiteralCNF compareLiteral = literal as NumericCompareLiteralCNF;
if (compareLiteral != null)
{
var assignment = compareLiteral.TryGetNumericFunctionAssignment();
if (assignment != null)
{
if (!compareLiteral.IsNegated)
{
state.AssignNumericFunction(assignment.Item1.FunctionAtom.Clone(), NumericFunction.UndefinedValue);
}
}
}
};
if (index >= conjuncts.Count)
{
yield return((IRelativeState)result.Clone());
}
else
{
var conjunct = conjuncts[index];
ClauseCNF clause = conjunct as ClauseCNF;
if (clause != null)
{
foreach (var literal in clause)
{
addLiteral(result, literal);
foreach (var item in EnumerateRelativeStatesByCNF(index + 1, conjuncts, result))
{
yield return(item);
}
removeLiteral(result, literal);
}
}
else
{
LiteralCNF literal = conjunct as LiteralCNF;
Debug.Assert(literal != null);
addLiteral(result, literal);
foreach (var item in EnumerateRelativeStatesByCNF(index + 1, conjuncts, result))
{
yield return(item);
}
removeLiteral(result, literal);
}
}
}
