| public PopFrame ( int framePointer ) : void | ||
| framePointer | int | Base of the frame we're popping off |
| return | void | |
private const byte NoRegister = 0xff; // Target register meaning not to write to register
// So here's append([], X, X). :
// MatchLiteral([], 0)
// MatchVarFirst(1) % This is actually a no-op
// MatchVar(1, 2)
// Return
//
// And here's append([H|T], X, [H|T1]) :- append(T, X, T1).
// MatchStructure(dot, 2, L1, 0)
// MatchVarFirst(0>0>3) % H is at 3
// MatchVarFirst(0>1>4) % T is at 4
// L1 MatchVarFirst(1) % Actually a no-op
// MatchStructure(dot, 2, L2, 2)
// MatchVar(3, 2>0)
// MatchVarFirst(5, 2>1) % T1 is at 5
// L2 Call(6, Fail, Succeed, append/3, register(4), register(2), register(5))
#endregion
#region Interpreter
internal IEnumerable <CutState> StackCall(PrologContext context)
{
int traceMark = context.MarkTrail();
// On entry, the stack pointer points at the base of our arguments.
int framePointer = context.MakeFrame(frameSize);
ushort pc = 0;
ushort writeModeEndAddress = 0; // We're in write mode if pc < writeModeEndAddress.
// ReSharper disable TooWideLocalVariableScope
// Resharper is confused - can't move this inside the while loop, or its lifetime changes.
ushort endOfBuilds; // PC of last call instruction whose arguments have been built.
// ReSharper restore TooWideLocalVariableScope
while (true)
{
switch ((Opcode)code[pc++])
{
#region Head opcodes
case Opcode.MatchLiteral:
{
object literal = GetLiteral(ref pc);
if (pc < writeModeEndAddress)
{
// Write mode
SetOperand(context, framePointer, ref pc, literal);
}
else
{
// Read mode
if (!Term.Unify(DecodeOperand(context, framePointer, ref pc), literal, context))
{
goto fail;
}
}
}
break;
case Opcode.MatchVarFirst:
{
if (pc < writeModeEndAddress)
{
// Write mode
Symbol name = GetSymbol(ref pc);
int register = code[pc++];
var l = new LogicVariable(name);
SetOperand(context, framePointer, ref pc, l);
if (register != NoRegister)
{
context.SetStack(framePointer, register, l);
}
}
else
{
pc += 2; // Skip over variable name.
int register = code[pc++];
// Read mode
object operand = DecodeOperand(context, framePointer, ref pc);
if (register != NoRegister)
{
context.SetStack(framePointer, register, operand);
}
}
}
break;
case Opcode.MatchVar:
{
object register = Register(context, framePointer, pc++);
if (pc < writeModeEndAddress)
{
// Write mode
SetOperand(context, framePointer, ref pc, register);
}
else
{
// Read mode
if (!Term.Unify(DecodeOperand(context, framePointer, ref pc), register, context))
{
goto fail;
}
}
}
break;
case Opcode.MatchStructure:
{
Symbol functor = GetSymbol(ref pc);
int arity = code[pc++];
ushort endAddress = GetUShort(ref pc);
if (pc < writeModeEndAddress)
{
// Write mode
SetOperand(context, framePointer, ref pc, new Structure(functor, new object[arity]));
}
else
{
// Read mode
object arg = DecodeOperand(context, framePointer, ref pc);
var s = arg as Structure;
if (s == null || !s.IsFunctor(functor, arity))
{
var l = arg as LogicVariable;
if (l == null)
{
goto fail;
}
l.UnifyWithStructure(new Structure(functor, new object[arity]));
writeModeEndAddress = endAddress;
}
}
}
break;
#endregion
#region Body opcodes: structure building
case Opcode.BuildStructure:
{
Symbol functor = GetSymbol(ref pc);
int arity = code[pc++];
SetOperand(context, framePointer, ref pc,
new Structure(functor, new object[arity]));
}
break;
case Opcode.BuildLiteral:
SetOperand(context, framePointer, ref pc, GetLiteral(ref pc));
break;
case Opcode.BuildVar:
{
Symbol name = GetSymbol(ref pc);
SetOperand(context, framePointer, ref pc, new LogicVariable(name));
}
break;
case Opcode.BuildReg:
object registerValue = Register(context, framePointer, pc++);
SetOperand(context, framePointer, ref pc, registerValue);
break;
#endregion
#region Body: control flow
case Opcode.CallWokenGoals:
case Opcode.Call:
case Opcode.CallPrimitive:
endOfBuilds = pc;
// ReSharper disable once InconsistentNaming
ushort succeedPC;
IEnumerator <CutState> iterator;
var failPC = StartCallInstruction(context, framePointer, ref pc, out succeedPC, out iterator);
while (true)
{
if (iterator == null || iterator.MoveNext())
{
// Call succeeds
if (succeedPC == SuccessContinuationPC)
{
yield return(CutState.Continue);
// If we get here, then our caller is requesting a redo
// Fall through and continue this iterator.
if (iterator == null)
{
goto fail; // Kluge: special case to handle CallWokenGoals instruction where there are no woken goals.
}
}
else
{
if (succeedPC > endOfBuilds)
{
// Haven't run the build instructions for next goal, so break out and run them.
break;
}
pc = (ushort)(succeedPC + 1); // StartCallInstruction assumes we've skipped over the opcode.
// succeedPC is address of call/callprimitive instruction; next byte is iterator register
failPC = this.StartCallInstruction(context, framePointer, ref pc, out succeedPC, out iterator);
// Continue while loop
}
}
else
{
// Call fails
switch (failPC)
{
case FailContinuationPC:
goto fail;
case CutContinuationPC:
goto cut;
default:
// failPC is address of call/callprimitive instruction; next byte is iterator register
pc = (ushort)(failPC + 1); // +1 because we're skipping over the opcode
iterator =
(IEnumerator <CutState>)context.GetStack(framePointer, code[pc++]);
if (iterator == null) // Kluge: special case to handle CallWokenGoals instruction where there are no woken goals.
{
goto fail;
}
failPC = GetUShort(ref pc);
succeedPC = GetUShort(ref pc);
break;
}
}
}
break;
#endregion
default:
Debug.Assert(false, "Bad opcode in byte compiled Prolog rule, pc=" + (pc - 1) + ", opcode=" + ((Opcode)code[pc - 1]));
break;
}
}
// The while loop above never terminates normally; it only yeilds or branches to one of the following labels
cut:
context.PopFrame(framePointer);
context.RestoreVariables(traceMark);
yield return(CutState.ForceFail);
fail:
context.PopFrame(framePointer);
context.RestoreVariables(traceMark);
}