public bool Retract(Term t, VarStack varStack, Term where)
{
string key = t.KbKey;
if (predefineds.Contains(key))
PrologIO.Error("retract of predefined predicate {0} not allowed", key);
PredicateDescr pd = this[key];
if (pd == null) return false;
#if persistent
if (pd is PersistentPredDescr)
{
((PersistentPredDescr)pd).Retract (t, varStack, where);
return true;
}
#endif
ClauseNode c = pd.GetClauseList(null, null);
ClauseNode prevc = null;
Term cleanTerm;
int top;
while (c != null)
{
cleanTerm = c.Term.CleanCopy();
top = varStack.Count;
if (cleanTerm.Unify(t, varStack)) // match found -- remove this term from the chain
{
if (prevc == null) // remove first clause
{
if (c.NextClause == null) // we are about to remove the last remaining clause for this predicate
{
predTable.Remove(key); // ... so remove its PredicateDescr as well
#if arg1index
pd.CreateFirstArgIndex (); // re-create
#endif
ResolveIndices();
}
else
pd.SetClauseListHead(c.NextClause);
}
else // not the first
{
prevc.NextClause = c.NextClause;
prevc = c;
pd.AdjustClauseListEnd();
#if arg1index
pd.CreateFirstArgIndex (); // re-create
#endif
}
return true; // possible bindings must stay intact (e.g. if p(a) then retract(p(X)) yields X=a)
}
Term s;
for (int i = varStack.Count - top; i > 0; i--) // unbind all vars that got bound by the above Unification
{
s = (Term)varStack.Pop();
s.Unbind();
}
prevc = c;
c = c.NextClause;
}
ResolveIndices();
return false;
}
public bool Unifiable(Term t, VarStack varStack) // as Unify, but does not actually bind
{
int top = varStack.Count;
bool result = Unify(t, varStack);
for (int i = varStack.Count - top; i > 0; i--) // unbind all varNoSet that got bound by Unify
{
Term s = (Term)varStack.Pop();
s.Unbind();
}
return result;
}