public IEnumerable <Pair <T, SubstitutionSet> > Unify(Stack <Name> stack, SubstitutionSet binding)
{
if (stack.Count == 0) //End stack
{
if (m_hasValue)
{
yield return(Tuples.Create(m_value, binding));
}
yield break;
}
TreeNode nodeToEvaluate;
Name term = stack.Pop();
if (!term.IsVariable)
{
int numOfTerms = term.NumberOfTerms;
if (numOfTerms == 1)
{
var selectedNodes = Enumerable.Empty <TreeNode>();
Name key = term;
if (key.IsUniversal)
{
if (m_universal != null)
{
selectedNodes = selectedNodes.Append(m_universal);
}
selectedNodes = selectedNodes.Union(GetNextLevel().SelectMany(p => p.Item2));
}
else
{
if (m_nextSymbol != null && m_nextSymbol.TryGetValue(key, out nodeToEvaluate))
{
selectedNodes = selectedNodes.Append(nodeToEvaluate);
}
if (m_universal != null)
{
selectedNodes = selectedNodes.Append(m_universal);
}
}
foreach (var pair in selectedNodes.SelectMany(n => n.Unify(stack, binding)))
{
yield return(pair);
}
}
else
{
if (m_nextComposed != null && m_nextComposed.TryGetValue(numOfTerms, out nodeToEvaluate))
{
using (var it = term.GetTerms().Reverse().GetEnumerator())
{
while (it.MoveNext())
{
stack.Push(it.Current);
}
}
foreach (var pair in nodeToEvaluate.Unify(stack, binding))
{
yield return(pair);
}
for (int i = 0; i < term.NumberOfTerms; i++)
{
stack.Pop();
}
}
if (m_universal != null)
{
foreach (var pair in m_universal.Unify(stack, binding))
{
yield return(pair);
}
}
}
if (m_nextVariable != null)
{
//Find bindings with stored variables
foreach (var pair in m_nextVariable)
{
var sub = new Substitution(pair.Key, new ComplexValue(term));
if (binding.Conflicts(sub))
{
continue;
}
var set = new SubstitutionSet(binding);
set.AddSubstitution(sub);
foreach (var r in pair.Value.Unify(stack, set))
{
yield return(r);
}
}
}
}
else
{
//Find bindings
var nextLevel = GetNextLevel();
foreach (var pair in nextLevel)
{
SubstitutionSet set = binding;
if (!pair.Item1.IsVariable || pair.Item1 != term)
{
//Very odd trick to make certainty work
var sub = new Substitution(term, new ComplexValue(pair.Item1, 1));
if (binding.Conflicts(sub))
{
continue;
}
set = new SubstitutionSet(set);
set.AddSubstitution(sub);
}
foreach (var node in pair.Item2)
{
foreach (var r in node.Unify(stack, set))
{
yield return(r);
}
}
}
}
stack.Push(term);
}
