[Rd] R-3.3.3/R-3.4.0 change in sys.call(sys.parent())

[Deepayan Sarkar]

On Thu, May 11, 2017 at 8:03 PM, William Dunlap <wdunlap at tibco.com> wrote:
> Here is a case where the current scheme fails:
>
>   > with(datasets::mtcars, xyplot(mpg~wt|gear)$call)
>   xyplot(substitute(expr), data, enclos = parent.frame())

Right, thanks. So I guess I can't avoid setting $call inside every method.

-Deepayan

> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
> On Thu, May 11, 2017 at 1:09 AM, Deepayan Sarkar <deepayan.sarkar at gmail.com>
> wrote:
>>
>> On Wed, May 10, 2017 at 2:36 AM, William Dunlap via R-devel
>> <r-devel at r-project.org> wrote:
>> > Some formula methods for S3 generic functions use the idiom
>> >     returnValue$call <- sys.call(sys.parent())
>> > to show how to recreate the returned object or to use as a label on a
>> > plot.  It is often followed by
>> >      returnValue$call[[1]] <- quote(myName)
>> > E.g., I see it in packages "latticeExtra" and "leaps", and I suspect it
>> > used in "lattice" as well.
>> >
>> > This idiom has not done good things for quite a while (ever?) but I
>> > noticed
>> > while running tests that it acts differently in R-3.4.0 than in R-3.3.3.
>> > Neither the old or new behavior is nice.  E.g., in R-3.3.3 we get
>> >
>> >> parseEval <- function(text, envir) eval(parse(text=text), envir=envir)
>> >> parseEval('lattice::xyplot(mpg~hp, data=datasets::mtcars)$call',
>> > envir=new.env())
>> > xyplot(expr, envir, enclos)
>> >
>> > and
>> >
>> >> evalInEnvir <- function(call, envir) eval(call, envir=envir)
>> >> evalInEnvir(quote(lattice::xyplot(mpg~hp, data=datasets::mtcars)$call),
>> > envir=new.env())
>> > xyplot(expr, envir, enclos)
>> >
>> > while in R-3.4.0 we get
>> >> parseEval <- function(text, envir) eval(parse(text=text), envir=envir)
>> >> parseEval('lattice::xyplot(mpg~hp, data=datasets::mtcars)$call',
>> > envir=new.env())
>> > xyplot(parse(text = text), envir = envir)
>> >
>> > and
>> >
>> >> evalInEnvir <- function(call, envir) eval(call, envir=envir)
>> >> evalInEnvir(quote(lattice::xyplot(mpg~hp, data=datasets::mtcars)$call),
>> > envir=new.env())
>> > xyplot(call, envir = envir)
>> >
>> > Should these packages be be fixed up to use just sys.call()?
>>
>> I admit to not understanding these things very well, but I'll try to
>> explain why I ended up with the usage I have. The main use of the
>> $call component within lattice is to use it in the summary method, as
>> in:
>>
>> > summary(xyplot(mpg~hp, data=mtcars))
>>
>> Call:
>> xyplot(mpg ~ hp, data = mtcars)
>>
>> Number of observations:
>> [1] 32
>>
>> Here is a minimal approximation to what I need: Here foo() and bar()
>> are generics producing objects of class "foobar", bar() calls foo()
>> with one argument changed, and the print() method for "foobar" is just
>> supposed to print the call that produced it:
>>
>> ########
>>
>> foo <- function(x, ...) UseMethod("foo")
>> bar <- function(x, ...) UseMethod("bar")
>> print.foobar <- function(x, ...) print(x$call)
>>
>> ## Using plain sys.call():
>>
>> foo.formula <- function(x, ...)
>> {
>>     ans <- structure(list(), class = "foobar")
>>     ans$call <- sys.call()
>>     ans
>> }
>>
>> bar.formula <- function(x, ..., panel)
>> {
>>     foo.formula(x, ..., panel = panel.bar)
>> }
>>
>> foo.table <- function(x, ...)
>> {
>>     ans <- foo.formula(Freq ~ Var1,
>>                        as.data.frame.table(x), ...)
>>     ans
>> }
>>
>> ## I would get
>>
>> foo(y ~ x)
>> # foo.formula(y ~ x)
>>
>> bar(y ~ x)
>> # foo.formula(x, ..., panel = panel.bar)
>>
>> foo(as.table(1:10))
>> # foo.formula(Freq ~ Var1, as.data.frame.table(x), ...)
>>
>> ## The last two are improved by
>>
>> foo.formula <- function(x, ...)
>> {
>>     ans <- structure(list(), class = "foobar")
>>     ans$call <- sys.call(sys.parent())
>>     ans
>> }
>>
>> bar(y ~ x)
>> ## bar.formula(y ~ x)
>>
>> foo(as.table(1:10))
>> ## foo.table(as.table(1:10))
>>
>> ########
>>
>> Adding
>>
>> ans$call[[1]] <- quote(foo)
>>
>> (or quote(bar) in bar.formula) is needed to replace the unexported
>> method name (foo.formula) with the generic name (foo), but that's
>> probably not the problem.
>>
>> With this approach in lattice,
>>
>> p <- some.function(...)
>> eval(p$call)
>>
>> usually works, but not always, if I remember correctly.
>>
>> I'm happy to consider more robust solutions. Maybe I just need to have a
>>
>> ...$call <- sys.call()
>>
>> statement in every method?
>>
>> -Deepayan
>
>