code: func (a *AggregateFuncExtractor) Leave(n ast.Node) (ast.Node, bool) {
  	switch v := n.(type) {
  	case *ast.AggregateFuncExpr:
  		a.inAggregateFuncExpr = false
  		a.AggFuncs = append(a.AggFuncs, v)
  	}
  	return n, true
  }
docs: // Leave implements Visitor interface.