public void Assert(Term assertion, bool asserta)
{
assertion = assertion.CleanCopy(); // make a fresh copy
Term head;
TermNode body = null;
if (assertion.Functor == Parser.IMPLIES)
{
head = assertion.Arg(0);
body = assertion.Arg(1).ToGoalList();
}
else
head = assertion;
if (head.IsVar) PrologIO.Error("Cannot assert a variable as predicate head");
string key = head.KbKey;
// A predefined predicate (which may also be defined as operator) may not be redefined.
// Operators ':-', ',', ';', '-->', '->' (precedence >= 1000) may also not be redefined.
if (predefineds.Contains(key) || (head.Precedence >= 1000))
PrologIO.Error("assert cannot be applied to predefined predicate or system operator {0}", assertion.Index);
PredicateDescr pd = (PredicateDescr)predTable[key];
#if persistent
if (pd != null && pd is PersistentPredDescr)
{
((PersistentPredDescr)pd).Assert (head);
return;
}
#endif
ClauseNode newC = new ClauseNode(head, body);
if (pd == null) // first head
{
SetClauseList(PredEnum.session, head.Functor, head.Arity, newC);
ResolveIndices();
}
else if (asserta) // at beginning
{
newC.NextClause = pd.ClauseNode; // pd.ClauseNode may be null
SetClauseList(PredEnum.session, head.Functor, head.Arity, newC);
#if arg1index
pd.CreateFirstArgIndex (); // re-create
#endif
}
else // at end
{
pd.AppendToClauseList(newC);
#if arg1index
pd.CreateFirstArgIndex (); // re-create
#endif
}
}
