private IEnumerable<bool> _cooperativeForce(StackContext sctx, Action<PValue> setReturnValue)
{
if (sctx == null)
throw new ArgumentNullException("sctx");
while (true)
{
//Check if evaluation resulted in exception
if (_exception != null)
throw _exception;
//Check if value is available
if (_value != null)
break;
//Prevent infinite loops
if (_blackHole.Trap())
continue; //If we have been trapped, check exception again
//Tag thunk as being evaluated
_blackHole = BlackHole.Active(Thread.CurrentThread.ManagedThreadId);
Debug.Indent();
//We need to save stack space here, so try to invoke via IStackAware
// Since most expressions are closures, this has a high success rate
var stackAware = _expr.Value as IStackAware;
if (stackAware != null)
{
//Exception handler defined in creation of cooperative context
var exprCtx = stackAware.CreateStackContext(sctx, _parameters);
sctx.ParentEngine.Stack.AddLast(exprCtx);
yield return true;
_value = exprCtx.ReturnValue;
}
else
{
try
{
_value = _expr.IndirectCall(sctx, _parameters);
}
catch (Exception ex)
{
_blackHole = _blackHole.Inactivate();
_value = PType.Null;
_exception = ex;
throw;
}
}
Debug.Unindent();
var t = _value.Value as Thunk;
if (t != null)
{
//Assimilate nested thunk
_blackHole = t._blackHole;
_expr = t._expr;
_parameters = t._parameters;
_value = t._value;
_exception = t._exception;
continue;
}
else
{
//Release expression
_expr = null;
_parameters = null;
_blackHole = _blackHole.Inactivate();
break;
}
}
setReturnValue(_value);
yield break;
}
