[Rd] Puzzled by eval

[Gabor Grothendieck]

This code which I think I wrote but might have gotten from elsewhere a
long time ago shows the environments that are searched from a given
function, in this case chart.RelativePerformance in
PerformanceAnalytics package.   Try it on some of your functions in
and out of packages to help determine the sequence of environments R
searches along:

library( PerformanceAnalytics )  ## change as needed
x <- environment(chart.RelativePerformance) ## change as needed
str(x)
while (!identical(x, emptyenv())) {
    p <- parent.env(x)
    cat("---- child is above this line and parent is below ----\n")
    str(p)
    if (isBaseNamespace(p)) cat("Same as .BaseNamespaceEnv\n")
    if (identical(p, baseenv())) cat("Same as baseenv()\n")
    if (identical(p, emptyenv())) cat("Same as emptyenv()\n")
    if (identical(p, globalenv())) cat("Same as globalenv()\n")
    x <- p
}

On Fri, Nov 6, 2015 at 9:47 AM, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
> On 06/11/2015 8:20 AM, Therneau, Terry M., Ph.D. wrote:
>>
>> Duncan,
>>     That's helpful.  Two follow-up questions:
>> 1. Where would I have found this information?  I had looked at eval and
>> model.frame.
>
>
> I think the best description is Luke's article on namespaces, "Name space
> management for R". Luke Tierney, R News, 3(1):2-6, June 2003. There's a link
> to it from the "Technical papers" section of the HTML help index.  There's
> also a short description of this in the R Language Definition manual in the
> "Search path" section 3.5.4.
>
>
>> 2. What stops the following code from falling down the same rabbit hole?
>> Shouldn't it
>> find base::cos first?
>>
>>      library(survival)
>>      cos <- lung
>>      coxph(Surv(time, status) ~ age, data=cos)
>
>
> If that code is in a function anywhere (package or not), cos will be a local
> variable created there in the evaluation environment created when you
> evaluate the function.  If you execute it at the command line, you'll create
> a variable called "cos" in the global environment.  Local variables come
> ahead of the 3 places I listed.  (This is why Luke's article is good:  it
> doesn't oversimplify.)
>
> There's one other twist.  Even with cos being a local variable, cos(theta)
> would find base::cos, because the evaluator knows it is looking for a
> function (since it's a function call) and will skip over the local dataframe
> named cos.
>
> Duncan Murdoch
>
>>
>> Terry T.
>>
>>
>> On 11/06/2015 07:51 AM, Duncan Murdoch wrote:
>>>
>>> On 06/11/2015 7:36 AM, Therneau, Terry M., Ph.D. wrote:
>>>>
>>>> I am currently puzzled by a seach path behavior.  I have a library of a
>>>> dozen routines
>>>> getlabs(), getssn(), getecg(), ... that interface to local repositories
>>>> and pull back
>>>> patient information.  All have a the first 6 arguments in common, and
>>>> immediately call a
>>>> second routine to do initial processing of these 6.  The functions "joe"
>>>> and "fred" below
>>>> capture the relevant portion of them.
>>>>      My puzzle is this: the last test in the "test" file works fine if
>>>> these routines are
>>>> sourced and executed at the command line, it fails if the routines are
>>>> bundled up and
>>>> loaded as a library. That test is motivated by a user who called his
>>>> data set "t", and
>>>> ended up with a match to base:::t instead of his data, resulting in a
>>>> strange error
>>>> message out of model.frame  --- you can always count on the users!
>>>> (There are a few
>>>> hundred.)
>>>>       I'm attempting to be careful with envr and enclos arguments -- how
>>>> does base end up
>>>> earlier in the search path?   Perhaps this is clearly stated in the docs
>>>> and just not
>>>> clear to me?  A working solution to the dilemma is of course more than
>>>> welcome.
>>>
>>>
>>> I haven't followed through all the details in fred(), but I can answer
>>> the last question.
>>> In package code, the search order is:
>>>
>>> - the package environment
>>> - the imports to the package (with base being an implicit import)
>>> - the global environment and the rest of the search list.
>>>
>>> In code sourced to the global environment, only the third of these is
>>> searched.  Since
>>> base is in the second one, it is found first in the package version.
>>>
>>> Duncan Murdoch
>
>
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