Issue with match.call

r

Solution

Your suspicion is exactly right.

The very simple solution is to evaluate the function in its parent’s context: replace `eval` with `eval.parent`.

myFunc <- function(x) {
  tmp <- match.call()
  tmp[[1]] <- quote(toupper)
  eval.parent(tmp)
}

Generally, the function `traceback` can help tremendously with debugging similar issues:

> tester()
Error in as.character(x) :
  cannot coerce type 'closure' to vector of type 'character'

Ok, but which “closure” (= function) are we talking about?

> traceback()
5: toupper(x = var)
4: eval(expr, envir, enclos)
3: eval(tmp) at #5
2: myFunc(var) at #5
1: tester()

The first line has the clue: `toupper(x = var)`. In the context of `tester`, `var` refers to the function (closure) `stats::var` which is found because its package is attached.

Problem

I wrote a function that uses `match.call`, and it works when I call the function directly, however, when the function is called within another function it breaks. I believe it has to do with how `match.call` handles environments, but I can't figure it out. Here is a reproducable example: ``` tester <- function() { var <- "helloworld" myFunc(var) } myFunc <- function(x) { tmp <- match.call() tmp[[1]] <- quote(toupper) eval(tmp) } tester() # error myFunc("helloworld") # works fine ``` I believe that when `myFunc` is called within `tester` it can't find `var` because it exists in the isolated environment of the `tester` function. Any ideas on how to get `myFunc` to work inside `tester` would be appreciated. I've tried changing the environment for `eval` and `match.call`, but to no avail.

Original source