Conventions: Use of globals and main functions

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.,

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.duncan at gmail.com 
<mailto:murdoch.duncan at 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