/// <summary>
/// Generates all possible PDDL states meeting conditions specified by the given constraint function. Lazy generated recursively via yield return.
/// </summary>
/// <param name="index">Current index in the predicates list.</param>
/// <param name="predicates">List of all grounded predicates.</param>
/// <param name="result">Current state being built.</param>
/// <param name="predicateConstraint">Predicate constraint function (returns true for positively constrained predicate, false for negatively constrained
/// predicate, or null for not constrained).</param>
/// <returns>All possible PDDL states meeting the conditions.</returns>
private static IEnumerable <IState> EnumerateStatesByPredicates(int index, List <IAtom> predicates, IState result, Func <IAtom, bool?> predicateConstraint)
{
if (index >= predicates.Count)
{
yield return((IState)result.Clone());
}
else
{
var predicate = predicates[index];
// predicate can be positively constrained, negatively constrained (not), or not constrained at all
var constraint = predicateConstraint(predicate);
if (constraint != null)
{
if (constraint.Value)
{
result.AddPredicate(predicate);
}
foreach (var item in EnumerateStatesByPredicates(index + 1, predicates, result, predicateConstraint))
{
yield return(item);
}
if (constraint.Value)
{
result.RemovePredicate(predicate);
}
}
else
{
// the predicate won't be contained
foreach (var item in EnumerateStatesByPredicates(index + 1, predicates, result, predicateConstraint))
{
yield return(item);
}
// the predicate will be contained
result.AddPredicate(predicate);
foreach (var item in EnumerateStatesByPredicates(index + 1, predicates, result, predicateConstraint))
{
yield return(item);
}
result.RemovePredicate(predicate);
}
}
}
