On 13-01-01 4:35 PM, Jeff Ryan wrote:
Happy 2013!
Can someone with more knowledge of edge case scoping/eval rules explain
what is happening below? Happens in all the versions of R I have on hand.
Even though it is used as a default in a number of places, the pos==-1
value is really poorly documented. You need to look in the source, in
particular src/main/envir.c, function pos2env. There you'll see that
pos==-1 is special cased to be the environment from which pos.to.env
(or as.environment in your case) was called. For non-negative values,
it indexes the search list (i.e. the list returned by search().) Other
values are errors.
The trouble in your examples is that this location varies. In Fn1, it
is being called in the ls() call. In Fn2, it is in the force() call.
In Fn3 and Fn4, it's the Fn3/Fn4 call.
In spite of what the docs say in ?get, I would rarely if ever use a pos
argument to as.environment. Use an environment and pass it as envir.
Duncan Murdoch
Behavior itself is confusing, but ?as.environment also provides no clue.
The term used in that doc is 'search list', which is ambiguous, but the
see also section mentions search(), so I would *think* that is what is
intended. Either way Fn1() below can't really be explained.
Major question is what in the world is Fn1 doing, and why is Fn2 not equal
to Fn3? [ Fn3/Fn4 are doing what I want. ]
Fn1 <- function(x="test",pos=-1,env=as.environment(pos)) {
ls(env)
}
Fn2 <- function(x="test",pos=-1,env=as.environment(pos)) {
force(env)
ls(env)
}
Fn3 <- function(x="test",pos=-1,env=as.environment(pos)) {
# should be the same as force() in Fn2, but not
# ?force
# Note:
#
# This is semantic sugar: just evaluating the symbol will do the
# same thing (see the examples).
env
ls(env)
}
Fn4 <- function(x="test",pos=-1,env=as.environment(pos)) {
# same as Fn3
env <- env
ls(env)
}
Fn1()
Fn2()
Fn3()
Fn4()
ls()
###################### output #########################
Fn1()
[1] "doTryCatch" "expr" "handler" "name" "parentenv"
Fn2()
[1] "env" "pos" "x"
Fn3()
[1] "Fn1" "Fn2" "Fn3" "Fn4"
Fn4()
[1] "Fn1" "Fn2" "Fn3" "Fn4"
### .GlobalEnv
ls()
[1] "Fn1" "Fn2" "Fn3" "Fn4"
R.version
_
platform x86_64-apple-darwin11.2.0
arch x86_64
os darwin11.2.0
system x86_64, darwin11.2.0
status
major 2
minor 15.1
year 2012
month 06
day 22
svn rev 59600
language R
version.string R version 2.15.1 (2012-06-22)
nickname Roasted Marshmallows
R.version
_
platform x86_64-apple-darwin11.2.0
arch x86_64
os darwin11.2.0
system x86_64, darwin11.2.0
status Under development (unstable)
major 3
minor 0.0
year 2012
month 12
day 28
svn rev 61464
language R
version.string R Under development (unstable) (2012-12-28 r61464)
nickname Unsuffered Consequences
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