[R] How to get the namespace of a function?
Gabor Grothendieck
ggrothendieck at gmail.com
Fri Feb 3 05:54:30 CET 2006
In thinking about this some more here is a slightly simpler
solution than my previous one:
library(zoo)
z <- ts(1:3)
f <- function(y) {
index <- local(function(x) index(x), .GlobalEnv)
index(y)
}
environment(f) <- baseenv()
f(z)
On 2/2/06, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> I think the issue in this case is the following aspect of UseMethod
> from ?UseMethod:
>
> "'UseMethod' and 'NextMethod' search for methods in
> two places: first in the environment in which the generic function
> is called, and then in the registration data base for the
> environment in which the generic is defined"
>
> Even if one is successful in calling a generic function such as index
> from a function f with NULL environment UseMethod will look into
> the environment within f (and not find it since its parent was set to
> NULL) and since in this case the methods were not registered by the
> package it does not find them in the package either. This could have
> worked somewhat more smoothly had the methods been registered.
>
> On 2/2/06, Duncan Murdoch <murdoch at stats.uwo.ca> wrote:
> > On 2/2/2006 5:56 PM, Berton Gunter wrote:
> > > Just echoing and slightly amplifying Gabor's comment...
> > >
> > > The semantics of R are really based on functional programming (LISP-like)
> > > rather than OOP (JAVA-like)? R's behavior is "proper" from that point of
> > > view; what is "improper" is Fernando's expectation that it should behave
> > > some other way.
> >
> > I don't think it's that so much as trying not to break old code. It
> > doesn't make sense to me that the search order within a namespace should
> > pass through the global environment, but something would break if it
> > didn't. (I suspect it's probably the old S3 object system, which
> > predates namespaces by a long time, but it's been a while since I've
> > thought about this.)
> >
> > Duncan Murdoch
> >
> >
> > > Of course, one can simulate anything with a Turing machine,
> > > but I consider Fernando's criticisms somewhat "unfair" because he is
> > > expecting R to behave like something he is familiar with rather than as it
> > > was designed to. For this reason, what bothers him seems wholly desirable to
> > > me -- I want there to be well-defined scoping convention (lexical scoping)
> > > for R to find free variables.
> > >
> > > Cheers,
> > >
> > > Bert
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: r-help-bounces at stat.math.ethz.ch
> > > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Duncan Murdoch
> > > Sent: Thursday, February 02, 2006 2:16 PM
> > > To: fsaldanha at alum.mit.edu
> > > Cc: r-help at stat.math.ethz.ch
> > > Subject: Re: [R] How to get the namespace of a function?
> > >
> > > On 2/2/2006 5:05 PM, Fernando Saldanha wrote:
> > >> I am trying to imitate "encapsulation" from other languages like Java
> > >> or C++. Coming from that background, it bothers me that I can commit
> > >> errors like the following:
> > >>
> > >>> x <- 1
> > >>> f <- function(z) { y <- x; y + 1 } # Mistake: I should have written y <-
> > > z
> > >>> f(10)
> > >> [1] 2
> > >>
> > >> In a language like Java the interpreter would have noticed that x was
> > >> an undeclared variable and an error message would be issued. R, on the
> > >> other hand, allows the code to run, as x exists in the global
> > >> environment. I was trying to avoid such situations by setting the
> > >> environment of f to be NULL. If there is a better way to catch this
> > >> type of errors I would be interested in knowing about it.
> > >
> > > Put your code in a package, and use a namespace. This isn't perfect,
> > > but it gives you more control than you have when running scripts at the
> > > console.
> > >
> > > There's an article by Luke Tierney in one of R News 3/1 that explains
> > > the search order when namespaces are involved.
> > >
> > > Duncan Murdoch
> > >> FS
> > >>
> > >> On 2/2/06, Duncan Murdoch <murdoch at stats.uwo.ca> wrote:
> > >>> On 2/2/2006 10:56 AM, Fernando Saldanha wrote:
> > >>>> I declared the environment of the function myfun to be NULL as follows:
> > >>>>
> > >>>> environment(myfun) <- NULL
> > >>> Since version 2.1.0, it's been recommended that you use
> > >>>
> > >>> environment(myfun) <- baseenv()
> > >>>
> > >>> and since 2.2.0, you'll get a warning when using NULL (and you'll get an
> > >>> error in 2.3.0). But why would you want to do that? What are you
> > >>> trying to achieve?
> > >>>
> > >>> Duncan Murdoch
> > >>>
> > >>>
> > >>>> Later on I called that myfun and got an error message because the
> > >>>> function index() in the zoo package was called inside myfun and was
> > >>>> not visible:
> > >>>>
> > >>>> Error in myfun(args) : couldn't find function "index"
> > >>>>
> > >>>> I tried to use zoo::index() instead of index(), but that did not work.
> > >>>> In fact, zoo::index does not work even in the command line:
> > >>>>
> > >>>>> z<-ts(1:5)
> > >>>>> z
> > >>>> Time Series:
> > >>>> Start = 1
> > >>>> End = 5
> > >>>> Frequency = 1
> > >>>> [1] 1 2 3 4 5
> > >>>>> index(z)
> > >>>> [1] 1 2 3 4 5
> > >>>>> zoo::index(z)
> > >>>> Error in loadNamespace(name) : package 'zoo' does not have a name space
> > >>>>
> > >>>> How can I qualify index() so that it is visible inside the body of
> > > myfun?
> > >>>> Thanks for any suggestions,
> > >>>>
> > >>>> FS
> > >>>>
> > >>>> ______________________________________________
> > >>>> R-help at stat.math.ethz.ch mailing list
> > >>>> https://stat.ethz.ch/mailman/listinfo/r-help
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> > >
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> >
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