public static LispEvaluationState Evaluate(LispHost host, LispExecutionState executionState)
{
var shouldDribbleReturnValue = executionState.StackFrame.Root.DribbleStream != null;
while (executionState.TryDequeueOperation(out var operation))
{
if (executionState.LastResult is LispError error)
{
// re-queue, because we can never finish
executionState.InsertOperation(operation);
error.StackFrame ??= executionState.StackFrame;
executionState.StackFrame.Root.OnErrorOccured(error, executionState.StackFrame);
return(LispEvaluationState.FatalHalt);
}
// value setting can only occur when evaluating a native macro or native function; if any of the set operations wants to halt, we do that below
var captureValueSetHalt = false;
var haltDueToValueSet = false;
var valueSet = new EventHandler <LispValueSetEventArgs>((s, e) =>
{
if (captureValueSetHalt)
{
haltDueToValueSet = haltDueToValueSet || e.HaltExecution;
}
});
executionState.StackFrame.Root.ValueSet += valueSet;
switch (operation)
{
case LispEvaluatorPopForTailCall tailPop:
{
// the shape of the operation stack at the time of a tail call should be either:
// pop
// tail-call-expression
// function-return
// or
// tail-call-expression
// function-return
ILispEvaluatorOperation tailCallExpression = null;
ILispEvaluatorOperation invocationExit = null;
if ((executionState.PeekOperation() is LispEvaluatorPopArgument pop &&
executionState.TryDequeueOperation(out var _) &&
executionState.PeekOperation() is LispEvaluatorObjectExpression &&
executionState.TryDequeueOperation(out tailCallExpression) &&
executionState.PeekOperation() is LispEvaluatorFunctionExit &&
executionState.TryDequeueOperation(out invocationExit)) ||
(executionState.PeekOperation() is LispEvaluatorObjectExpression &&
executionState.TryDequeueOperation(out tailCallExpression) &&
executionState.PeekOperation() is LispEvaluatorFunctionExit &&
executionState.TryDequeueOperation(out invocationExit)))
{
var concreteInvocationExit = (LispEvaluatorFunctionExit)invocationExit;
Debug.Assert(ReferenceEquals(tailPop.Function, concreteInvocationExit.Function));
// restore the tail call operation and pop the stack
executionState.InsertOperation(concreteInvocationExit.WithoutFramePop());
executionState.InsertOperation(tailCallExpression);
executionState.StackFrame.CopyLocalsToParentForTailCall(host.CurrentPackage, new HashSet <string>(tailPop.InvocationArgumentNames));
executionState.StackFrame = executionState.StackFrame.Parent;
}
internal bool TryDequeueOperation(out ILispEvaluatorOperation operation)
{
operation = default;
if (_operationQueue.Count > 0)
{
operation = _operationQueue[0];
_operationQueue.RemoveAt(0);
return(true);
}
return(false);
}
internal void InsertOperation(ILispEvaluatorOperation operation)
{
_operationQueue.Insert(0, operation);
}
