[Rd] how to start local scope?

[Tamas K Papp]

How can I start a local scope inside an R function?  Eg in

> b
Error: object "b" not found
> f <- function() {
+   {
+     b <- 1
+   }
+   b+2
+ }
> f()
[1] 3

I would like f() to report an error, not finding b.  I am thinking
about something like let in Scheme/Lisp.

Thanks,

Tamas