ExecutionResults OnSetUnboundVariable(WamInstruction instruction)
{
if (CurrentStructure == null)
{
throw new InvalidOperationException("No current structure.");
}
CurrentStructureIndex += 1;
if (CurrentStructureIndex >= CurrentStructure.Functor.Arity)
{
throw new InvalidOperationException("Current structure arity exceeded.");
}
SetRegister(instruction.TargetRegister, CreateVariable());
CurrentStructure.Children[CurrentStructureIndex] = GetRegister(instruction.TargetRegister);
InstructionPointer = InstructionPointer.GetNext();
return(ExecutionResults.None);
}
ExecutionResults OnUnifyBoundVariable(WamInstruction instruction)
{
CurrentStructureIndex += 1;
if (CurrentUnifyMode == UnifyModes.Read)
{
if (!Unify(GetRegister(instruction.TargetRegister), CurrentStructure.Children[CurrentStructureIndex]))
{
return(ExecutionResults.Backtrack);
}
}
else // write
{
CurrentStructure.Children[CurrentStructureIndex] = GetRegister(instruction.TargetRegister);
}
InstructionPointer = InstructionPointer.GetNext();
return(ExecutionResults.None);
}
ExecutionResults OnLibraryCallFunction(WamInstruction instruction, Function function)
{
var functionArguments = new CodeTerm[instruction.Functor.Arity];
for (int index = 0; index < instruction.Functor.Arity; ++index)
{
functionArguments[index] = Evaluate(ArgumentRegisters[index]).GetCodeTerm();
}
CodeTerm functionResult;
try
{
functionResult = function.FunctionDelegate(functionArguments);
}
catch
{
// Backtrack on exception.
//
return(ExecutionResults.Backtrack);
}
try
{
var functionResultValue = (CodeValue)functionResult;
if (Convert.ToBoolean(functionResultValue.Object))
{
InstructionPointer = InstructionPointer.GetNext();
return(ExecutionResults.None);
}
else
{
// Result converts to false.
//
return(ExecutionResults.Backtrack);
}
}
catch
{
// Result cannot be converted to a boolean.
//
return(ExecutionResults.Backtrack);
}
}
ExecutionResults OnCall(WamInstruction instruction)
{
var instructionPointer = GetInstructionPointer(instruction.Functor, 0);
if (instructionPointer == WamInstructionPointer.Undefined)
{
return(ExecutionResults.Failure);
}
if (StackIndex >= StackSizeLimit)
{
return(ExecutionResults.Failure);
}
ReturnInstructionPointer = InstructionPointer.GetNext();
CutChoicePoint = ChoicePoint;
TemporaryRegisters.Clear();
StackIndex += 1;
InstructionPointer = instructionPointer;
return(ExecutionResults.None);
}
ExecutionResults OnGetUnboundVariable(WamInstruction instruction)
{
SetRegister(instruction.TargetRegister, GetRegister(instruction.SourceRegister));
InstructionPointer = InstructionPointer.GetNext();
return(ExecutionResults.None);
}
ExecutionResults OnPutStructure(WamInstruction instruction)
{
SetRegister(instruction.TargetRegister, CreateCompoundTerm(instruction.Functor));
InstructionPointer = InstructionPointer.GetNext();
return(ExecutionResults.None);
}
ExecutionResults OnPutValue(WamInstruction instruction)
{
SetRegister(instruction.TargetRegister, instruction.ReferenceTarget);
InstructionPointer = InstructionPointer.GetNext();
return(ExecutionResults.None);
}
ExecutionResults OnNoop(WamInstruction instruction)
{
InstructionPointer = InstructionPointer.GetNext();
return(ExecutionResults.None);
}