code: func (s *callStack) getSelfBinding() selfBinding {
  	for i := len(s.stack) - 1; i >= 0; i-- {
  		if s.stack[i].isCall {
  			return s.stack[i].env.selfBinding
  		}
  	}
  	panic(fmt.Sprintf("malformed stack %v", dumpCallStack(s)))
  }
docs: // getSelfBinding resolves the self construct