我想换出一些用户写的代码。表达式就像一个列表，但我不知道如何更新它们。我可以append()，但不能replace()。

orig_code <-
  parse(text = 
    "library(tidyverse)   
    list_1 <- list(a = 1, b = 2)"
  )

new_code <- parse(text = "list_1 <- list(a = 1:3)")

# I can append
append(
  x = orig_code,
  values = new_code
)
#> expression(
#>   library(tidyverse), 
#>   list_1 <- list(a = 1, b = 2), 
#>   list_1 <- list(a = 1:3)
#> )

# but not replace
replace(
  x = orig_code,
  list = 2,
  values = new_code
)
#> expression(
#>   library(tidyverse), 
#>   list_1 <- list(a = 1, b = 2)
#> )

# or reassign
orig_code[[2]] <- new_code

orig_code
#> expression(
#>   library(tidyverse), 
#>   list_1 <- list(a = 1, b = 2)
#> )

由reprex package（v0.3.0）于2020-07-05创建