ESS assigns .Last.value to the wrong place in R
Wed, 7 Aug 2002 15:58:35 -0400
I repeat my emails of 11/15/01 and 2/26/02, since it looks like this ESS bug is
still not fixed in ESS 5.1.23, and I think some resolution is needed.
When help() is invoked, ESS makes a copy of .Last.value in the .GlobalEnv,
which is *not* where R normally stores it (R stores it in package:base).
When this copy becomes stale it leads to wrong answers. The bug is in
essd-r.el, lines 63-64:
. ".Last.value <- get(\".ess.lvsave\",inherits=TRUE)\n") ; envir=1
which should be changed (as I have done on my machine) to:
. "assign(\".Last.value\", .ess.lvsave, envir=NULL)\n") ; package:base
Here's an example of how things can go wrong:
R> ?seq # At this point a stale copy of .Last.value is written to pos=1
R> .Last.value # WHOOPS! WRONG VALUE!
R> find(".Last.value") # The right value is masked by the stale copy
 ".GlobalEnv" "package:base"
Whenever I bring this up, a debate begins over who should change (ESS or R).
In particular, my solution will not work if package:base is "sealed". Here's
the tail end of our last discussion:
Rich Heiberger <email@example.com> wrote:
> ... The effect of sealing package:base from the user means that R will have
> to store .Last.value in .GlobalEnv, which is the place ESS is using. This
> in effect is your solution 2) Change R to store .Last.value in .GlobalEnv
> Net result, ESS does not change behavior, R has already promised to
> change behavior.
and Kurt Hornik <firstname.lastname@example.org> replied:
> Not at all. Sealing base does not mean that .Last.value needs to be
> stored in the user's workspace. The standard approach would be to use
> dynamic variables which are in fact functions with internal state
> (typically maintained in their environments). E.g., .libPaths() in R
> 1.4 or better illustrates the idea. There might be a .Last.value()
> along these lines. The most prominent example is options() which is
> used for manipulating .Options (see also the R FAQ): this is currently
> visible to the user but it really should not.
> Let me discuss our strategy re .Last.value with some r-core members.
Also, Rodney Sparapani <email@example.com> suggested:
> I may be in way over my head here. But, I think there is a 4th solution.
> Have ESS save .Last.value as some other variable in .GlobalEnv like
> .Last.value.saved. That way .Last.value would not be hidden, and it could
> still be retreived if someone had done a help() or whatever.
Any more thoughts?
-- David Brahm (firstname.lastname@example.org)
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