[Rd] The enclosed environment does not work as expected

[Eric Berger]

Hi Jiefei,
This is related to "lazy evaluation". Alternatives for dealing with it are
discussed here:

https://stackoverflow.com/questions/29084193/how-to-not-fall-into-rs-lazy-evaluation-trap

HTH,
Eric


On Sun, Apr 3, 2022 at 6:32 AM Jiefei Wang <szwjf08 using gmail.com> wrote:

> Hi,
>
> It seems like the enclosed environment does not work well with the
> loop. Here is a simple example
> ```
> FuncGenerator <- function(value){
>     function() message(value)
> }
>
> funcSets <- list()
> for(i in 1:2)
>     funcSets[[i]] <- FuncGenerator(i)
>
> environment(funcSets[[1]])$value
> # [1] 2
> environment(funcSets[[2]])$value
> # [1] 2
> ```
> The output from the last two lines is simply 2. I expect the first
> should be 1 and the second is 2. However, if I ask R to execute the
> message function before accessing its environment, the result is
> correct again.
>
> ```
> FuncGenerator <- function(value){
>     function() message(value)
> }
>
> funcSets <- list()
> for(i in 1:2)
>     funcSets[[i]] <- FuncGenerator(i)
>
> ## Ask to evaluate the function
> for(i in 1:2){
>     funcSets[[i]]()
> }
> # 1
> # 2
> environment(funcSets[[1]])$value
> # [1] 1
> environment(funcSets[[2]])$value
> # [1] 2
> ```
> This does not make any sense to me since the function simply prints
> out its variable `value`. It should not change the value of the
> variable, so I think this might be a bug in the code optimizer. This
> issue can only be corrected by the loop(like the second example),
> manually evaluating the function without the loop will give you the
> same result as the first example.
>
> Here is my session information
> > sessionInfo()
> R version 4.1.2 (2021-11-01)
> Platform: x86_64-w64-mingw32/x64 (64-bit)
> Running under: Windows 10 x64 (build 19044)
>
>
> Best,
> Jiefei
>
> ______________________________________________
> R-devel using r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

	[[alternative HTML version deleted]]