tracerr.go
func (s *stackFrame) string() string {
	return fmt.Sprintf("%s (%s:%d)", s.function, s.file, s.line)
}
func (s *stackFrame) string() string {
	return fmt.Sprintf("%s (%s:%d)", s.function, s.file, s.line)
}
// string converts a given stack frame to a formated string.