以函数作为输入并在调用时使其表达式可见的函数

Question

在this SO question的基础上，我想编写一个通过（1）设置每行可见的()和（2）将withAutoprint({})环绕在函数主体周围来操纵其他函数的函数。首先，尽管我对trace()的某些调用会产生我想要的结果，但是以某种方式我无法弄清楚。

这是一个简单的示例：

# Input function foo
foo <- function(x)
{
  line1 <- x
  line2 <- 0
  line3 <- line1 + line2
  return(line3)
}

# some function which alters foo (here called make_visible() )
foo2 <- make_visible(foo)

# so that foo2 looks like this after being altered
foo2 <- function(x)
{
 withAutoprint({
  (line1 <- x)
  (line2 <- 0)
  (line3 <- line1 + line2)

  (return(line3))
 })
}

# example of calling foo2 and desired output/result
> foo2(2)
> (line1 <- x)
[1] 2
> (line2 <- 0)
[1] 0
> (line3 <- line1 + line2)
[1] 2
> (return(line3))
[1] 2

Answer 1

我自己想出了一种使用以下功能的方式：

reveal <- function(.f) {

  if (typeof(.f) %in% c("special", "builtin")) {
    stop("reveal cannot be applied to primitive functions")
  }

  fct_formals <- formals(.f)
  fct_body <- body(.f)[-1]


  .f1 <- function(x) {
    (x) 
  }

  .f1_body <- body(.f1)[-1]

  .f2 <- function() {}

  for (i in seq_along(1:length(fct_body))) {

    .f1_body[[1]][[2]]<- fct_body[[i]]

    body(.f2)[[1+i]] <- .f1_body[[1]]

  }

  .f2_body <- body(.f2)[-1]


  .f3 <- function() {

    withAutoprint({
      x
    })

  }

  for (j in seq_along(1:length(.f2_body))) {

    body(.f3)[[2]][[2]][[1+j]] <- .f2_body[[j]]

  }

  formals(.f3) <- fct_formals

  .f3

}

将产生以下结果：

foo2 <- reveal(foo)
foo2(1)
> (line1 <- x)
> [1] 1
> (line2 <- 0)
> [1] 0
> (line3 <- line1 + line2)
> [1] 1
> (return(line3))
> [1] 1