Restrict access to variables in parent environment

On Fri, May 14, 2010 at 10:13 AM, Simon Urbanek
<simon.urbanek at r-project.org> wrote:

On May 14, 2010, at 10:29 AM, Jeff Ryan wrote:

This isn't like a local variable though, since any function above the
baseenv() in the search path will also not be found.

Yes, but that is a consequence of the request and hence intended. You can always either specify the full path to the function or assign locally any functions you'll need:

f = function(a) stats::rnorm(b)
environment(f) <- baseenv()
f()

Error in stats::rnorm(b) : object 'b' not found

f = function(a) { rnorm=stats::rnorm; rnorm(b) }
environment(f) <- baseenv()
f()

Error in rnorm(b) : object 'b' not found

Alternatively you can use any environment up the search path hoping that those won't define further variables.

But back to the original question -- if taken literally, it's quite useless since it corresponds to using emptyenv() instead of baseenv() which means that you can't do anything:

local(1+1,emptyenv())

Error in eval(expr, envir, enclos) : could not find function "+"


So likely the only useful(?) distinction would be to allow function lookup the regular way but change only the variable lookup to not look beyond the current environment. That is stretching it, though...

I didn't think of the corner cases. I'm OK with stats::rnorm or
stats:::rnorm. But '{' is not recognized. How to make it be
recognized?

f=function(a) base::rnorm(b)
environment(f)=mini.env
mini.env=new.env(parent=emptyenv())
import=c("{","::","+","rnorm") # add all functions you want to use
for (fn in import) mini.env[[fn]] = get(fn)

f=function(a) rnorm(a+b)
environment(f)=mini.env

f(1)

b=1
f=function() {
 stats::rnorm(b)
}
f()
#environment(f)=base()
environment(f)=emptyenv()
f()

Cheers,
Simon

f

function(a) { rnorm(b) }
<environment: base>

f()

Error in f() : could not find function "rnorm"

Jeff

On Fri, May 14, 2010 at 9:20 AM, Hadley Wickham <hadley at rice.edu> wrote:

Hello All,

By default, a reference of a variable in a function cause R to look
for the variable in the parent environment if it is not available in
the current environment (without generating any errors or warnings).
I'm wondering if there is a way to revert this behaviors, such that it
will not look for the parent environment and will generate an error if
the variable is not available in the current environment. Is this
tuning has to be done at the C level?

Try this:
b <- 1
f <- function(a) {
b
}

environment(f) <- baseenv()
f()

Hadley

--
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/

--
Jeffrey Ryan
jeffrey.ryan at insightalgo.com

ia: insight algorithmics
www.insightalgo.com

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-- 
Tom