On 26/08/2019 1:58 p.m., William Dunlap wrote:
Duncan Murdoch wrote:
> Scripts are for throwaways, not for anything worth keeping.
I totally agree and have a tangentially relevant question about the <<-
operator. Currently 'name <<- value' means to look up the environment
stack until you find 'name' and (a) if you find 'name' in some frame
bind it to a new value in that frame and (b) if you do not find it make
a new entry for it in .GlobalEnv.
Should R deprecate the second part of that and give an error if 'name'
is not already present in the environment stack? This would catch
misspelling errors in functions that collect results from recursive
calls. E.g.,
I like that suggestion. Package tests have been complaining about
packages writing to .GlobalEnv for a while now, so there probably aren't
many instances of b) in CRAN packages; that change might be relatively
painless.
Duncan Murdoch
collectStrings <- function(list) {
strings <- character() # to be populated by .collect
.collect <- function(x) {
if (is.list(x)) {
lapply(x, .collect)
} else if (is.character(x)) {
strings <<- c(strings, x)
}
misspelledStrings <<- c(strings, names(x)) # oops, would like
to be told about this error
NULL
}
.collect(list)
strings
}
This gives the incorrect:
> collectStrings(list(i="One", ii=list(a=1, b="Two")))
[1] "One" "Two"
> misspelledStrings
[1] "One" "Two" "i" "ii"
instead of what we would get if 'misspelledStrings' were 'strings'.
> collectStrings(list(i="One", ii=list(a=1, b="Two")))
[1] "One" "Two" "a" "b" "i" "ii"
If someone really wanted to assign into .GlobalEnv the assign() function
is available.
In S '<<-' only had meaning (b) and R added meaning (a). Perhaps it is
time to drop meaning (b). We could start by triggering a warning about
it if some environment variable were set, as is being done for
non-scalar && and ||.
Bill Dunlap
TIBCO Software
wdunlap tibco.com <http://tibco.com>
On Sun, Aug 25, 2019 at 5:09 PM Duncan Murdoch <murdoch.dun...@gmail.com
<mailto:murdoch.dun...@gmail.com>> wrote:
On 25/08/2019 7:09 p.m., Cyclic Group Z_1 wrote:
>
>
> This is a fair point; structuring functions into packages is
probably ultimately the gold standard for code organization in R.
However, lexical scoping in R is really not much different than in
other languages, such as Python, in which use of main functions and
defining other named functions outside of main are encouraged. For
example, in Scheme, from which R derives its scoping rules, the
community generally organizes code with almost exclusively functions
and few non-function global variables at top level. The common use
of globals in R seems to be mostly a consequence of historical
interactive use and, relatedly, an inherited practice from S.
>
> It is true, though, that since anonymous functions (such as in
lapply) play a large part in idiomatic R code, as you put it,
"[l]exical scoping means that all of the problems of global
variables are available to writers who use main()." Nevertheless,
using a main function with other functions defined outside it seems
like a good quick alternative that offers similar advantages to
making a package when functions are tightly coupled to the script
and the project may not be large or generalizable enough to warrant
making a package.
>
I think the idea that making a package is too hard is just wrong.
Packages in R have lots of requirements, but nowadays there are tools
that make them easy. Eleven years ago at UseR in Dortmund I wrote a
package during a 45 minute presentation, and things are much easier now.
If you make a complex project without putting most of the code into a
package, you don't have something that you will be able to modify in a
year or two, because you won't have proper documentation.
Scripts are for throwaways, not for anything worth keeping.
Duncan Murdoch
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