[R] eval and evironments: call local function in a global function

[Gabor Grothendieck]

I am not sure what the purpose of workspace is so I
have eliminated it in the following.  We just use the
environment within main and when main exits all its
variables go too so that seems sufficient.

fun.global <- function() { message('fun.global'); setVar(5) }

main <- function() {
	l.var <- 0
	setVar <- function(value) { message("set Var"); l.var <<- value }
	environment(fun.global) <- environment()
	fun.global()
	print(l.var)
}
main()

We could also recognize that there is an implicit object here with
methods setVar and fun.global and property l.var so using proto:

library(proto)
fun.global <- function(obj) { message("setVar"); obj$setVar(5) }

main <- function() {
    p <- proto(l.var = 0,
           setVar = function(obj, value) { message("setVar");
obj$l.var <- value },
           fun.global = fun.global)
    p$fun.global()
    print(p$l.var)
}
main()

On Thu, Aug 20, 2009 at 4:27 AM, Renaud Gaujoux<getoxxx at gmail.com> wrote:
> Hi,
>
> in my project I want the user to be able to write hook functions that are in
> turn called in my main code. I'd like the user's hooks to be able to call
> some function that set a variable outside their running environment. The
> trick is that this variable is not global, but defined on runtime before
> calling the hooks, and I don't want to leave any trace (i.e. global
> variables) after the main code has finished.
>
> I thought that the following would work but it doesn't. I guess I got too
> messy with environment and enclosures:
>
> # global function defined by the user
> fun.global <- function(){
>   message('fun.global')
>   setVar(5) #
> }
>
>
> # my main code
> main <- function(){
>   message('main')
>
>   # define a function to set some local variable
>   setVar <- local({
>   l.var <- 0
>   function(value){
>       message('setVar')
>      l.var <<- value
>   }
>   })
>   .workspace <- environment(setVar)
>   environment(setVar) <- new.env()
>
>   eval(fun.global(), enclos=environment(setVar))
>   print(get('l.var', envir=.workspace, inherits=FALSE))
> }
>
> main()
>
> I get the following output:
>> main
>> fun.global
>> Error in fun.global() : could not find function "setVar"
>
> There is definitely a problem of lookup somewhere. I first tried without
> eval, as I thought that function setVar would then be defined in a parent
> environment of the call to fun.global, but it does not work either.
> Can anybody tell me what's the problem and how I should do my stuff?
>
> Thanks,
> Renaud
>
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