Scoping and functions in R 2.11.1 : What's going wrong?

Question

This question comes from a range of other questions that all deal with essentially the same problem. For some strange reason, using a function within another function someti

Answer 1

As Dirk mentioned in his answer, there isn't actually a problem with the code that you posted. In the links you posted in the question, there seems to be a common theme: some_function contains code that messes about with environments in some way. This messing is either explicit, using new.env and with or implicitly, using a data argument, that probably has a line like

y <- eval(substitute(y), data)

The moral of the story is twofold. Firstly, try to avoid explicitly manipulating environments, unless you are really sure that you know what you are doing. And secondly, if a function has a data argument then put all the variables that you need the function to use inside that data frame.

Answer 2

There are undoubtedly bugs in R, but a lot of the issues that people have been having are quite often errors in the implementation of some_function, not R itself. R has scoping rules ( see http://cran.r-project.org/doc/manuals/R-intro.html#Scope) which when combined with lazy evaluation of function arguments and the ability to eval arguments in other scopes are extremely powerful but which also often lead to subtle errors.

Answer 3

Well there is no problem in what you posted:

/tmp$ cat joris.r 
#!/usr/bin/r -t

some_function <- function(y) y^2

ff <- function(x){
    y <- 4
    some_function(y)  # so we expect 16
}
print(ff(3))          # 3 is ignored
$ ./joris.r 
[1] 16
/tmp$

Could you restate and postan actual bug or misfeature?

Answer 4

R has both lexical and dynamic scope. Lexical scope works automatically, but dynamic scope must be implemented manually, and requires careful book-keeping. Only functions used interactively for data analysis need dynamic scope, so most authors (like me!) don't learn how to do it correctly.

See also: the standard non-standard evaluation rules.