public void PushContext(WamInstructionStream instructionStream)
{
if (instructionStream == null)
{
throw new ArgumentNullException("instructionStream");
}
var context = new WamContext();
_contextStack.Push(context);
CurrentContext = context;
State = WamMachineStates.Run;
InstructionPointer = new WamInstructionPointer(instructionStream);
ReturnInstructionPointer = WamInstructionPointer.Undefined;
StackIndex = 0;
Environment = null;
ChoicePoint = null;
ArgumentRegisters.Clear();
TemporaryRegisters.Clear();
CurrentStructure = null;
CurrentStructureIndex = -1;
}
bool Backtrack()
{
if (State != WamMachineStates.Backtrack)
{
throw new InvalidOperationException("Backtrack not required.");
}
if (ChoicePoint == null)
{
return(false);
}
UnwindTrail();
Environment = ChoicePoint.Environment;
StackIndex = ChoicePoint.StackIndex;
ReturnInstructionPointer = ChoicePoint.ReturnInstructionPointer;
ArgumentRegisters.Copy(ChoicePoint.ArgumentRegisters);
CutChoicePoint = ChoicePoint.CutChoicePoint;
InstructionPointer = ChoicePoint.BacktrackInstructionPointer;
PredicateEnumerator = ChoicePoint.PredicateEnumerator;
return(true);
}
