R devel - Jun 2010 - codetools: Suggestion to detect potentially unassigned variables

This is just a note/wishlist/for the record:

With

foo1 <- function() {
  res;
}

foo2 <- function() {
  for (i in c()) res <- 1;
  res;
}

foo3 <- function() {
  while (FALSE) res <- 1;
  res;
}

foo4 <- function() {
  if (FALSE) res <- 1;
  res;
}

we get:
> foo1()
Error in foo1() : object 'res' not found
> foo2()
Error in foo2() : object 'res' not found
> foo3()
Error in foo3() : object 'res' not found
> foo4()
Error in foo4() : object 'res' not found


Running R CMD check on R v2.11.1pat we get:

* checking R code for possible problems ... NOTE
foo1: no visible binding for global variable 'res'

An improvement would be to also report that:

foo2: variable 'res' may not be assigned
foo3: variable 'res' may not be assigned
foo4: variable 'res' may not be assigned

/Henrik