R devel - Mar 2017 - `[` not recognized as a primitive in certain cases.

Dear,

I have noticed this problem while looking at the following question on
Stackoverflow :

http://stackoverflow.com/questions/42894213/s4-class-subset-inheritance-with-additional-arguments

While going through callNextMethod, I've noticed the following odd
behaviour:

mc <- call("[",iris,2,"Species")

mc[[1]]
## `[`

is.primitive(`[`)
## [1] TRUE

is.primitive(mc[[1]])
## [1] FALSE
# Expected to be TRUE

mc2 <- as.call(list(`[`,iris,2,"Species"))

is.primitive(mc2[[1]])
## [1] TRUE

So depending on how I construct the call (using call() or as.call() ), the
function `[` is or is not recognized as a primitive by is.primitive()

The behaviour is counterintuitive and -unless I miss something obvious
here- likely to be a bug imho. I immediately admit that my C chops aren't
sufficient to come up with a patch.

Cheers
Joris

-- 
Joris Meys
Statistical consultant

Ghent University
Faculty of Bioscience Engineering
Department of Mathematical Modelling, Statistics and Bio-Informatics

tel :  +32 (0)9 264 61 79
Joris.Meys at Ugent.be
-------------------------------
Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php

	[[alternative HTML version deleted]]

There is a difference between the symbol and the function (primitive
or closure) to which it is bound.

This:
mc2 <- as.call(list(`[`,iris,2,"Species"))

Evaluates `[` to its value, in this case the primitive object, and the
primitive itself is incorporated into the returned call.

If you were to do this:
mc2 <- as.call(list(quote(`[`),iris,2,"Species"))

The `[` would _not_ be evaluated, quote() would return the symbol, and
the symbol would end up in the call.

The two forms have virtually identical behavior as long as the call
ends up getting evaluated in the same environment.

On Tue, Mar 28, 2017 at 3:03 AM, Joris Meys <jorismeys at gmail.com>
wrote:
> Dear,
>
> I have noticed this problem while looking at the following question on
> Stackoverflow :
>
>
http://stackoverflow.com/questions/42894213/s4-class-subset-inheritance-with-additional-arguments
>
> While going through callNextMethod, I've noticed the following odd
> behaviour:
>
> mc <- call("[",iris,2,"Species")
>
> mc[[1]]
> ## `[`
>
> is.primitive(`[`)
> ## [1] TRUE
>
> is.primitive(mc[[1]])
> ## [1] FALSE
> # Expected to be TRUE
>
> mc2 <- as.call(list(`[`,iris,2,"Species"))
>
> is.primitive(mc2[[1]])
> ## [1] TRUE
>
> So depending on how I construct the call (using call() or as.call() ), the
> function `[` is or is not recognized as a primitive by is.primitive()
>
> The behaviour is counterintuitive and -unless I miss something obvious
> here- likely to be a bug imho. I immediately admit that my C chops
aren't
> sufficient to come up with a patch.
>
> Cheers
> Joris
>
> --
> Joris Meys
> Statistical consultant
>
> Ghent University
> Faculty of Bioscience Engineering
> Department of Mathematical Modelling, Statistics and Bio-Informatics
>
> tel :  +32 (0)9 264 61 79
> Joris.Meys at Ugent.be
> -------------------------------
> Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

?typeof? is your friend here:
> typeof(`[`)
[1] "special"
> typeof(mc[[1]])
[1] "symbol"
> typeof(mc2[[1]])
[1] "special"

so mc[[1]] is a symbol, and thus not a primitive.

- Lukas
> On 28 Mar 2017, at 14:46, Michael Lawrence <lawrence.michael at
gene.com> wrote:
> 
> There is a difference between the symbol and the function (primitive
> or closure) to which it is bound.
> 
> This:
> mc2 <- as.call(list(`[`,iris,2,"Species"))
> 
> Evaluates `[` to its value, in this case the primitive object, and the
> primitive itself is incorporated into the returned call.
> 
> If you were to do this:
> mc2 <- as.call(list(quote(`[`),iris,2,"Species"))
> 
> The `[` would _not_ be evaluated, quote() would return the symbol, and
> the symbol would end up in the call.
> 
> The two forms have virtually identical behavior as long as the call
> ends up getting evaluated in the same environment.
> 
> On Tue, Mar 28, 2017 at 3:03 AM, Joris Meys <jorismeys at gmail.com>
wrote:
>> Dear,
>> 
>> I have noticed this problem while looking at the following question on
>> Stackoverflow :
>> 
>>
http://stackoverflow.com/questions/42894213/s4-class-subset-inheritance-with-additional-arguments
>> 
>> While going through callNextMethod, I've noticed the following odd
>> behaviour:
>> 
>> mc <- call("[",iris,2,"Species")
>> 
>> mc[[1]]
>> ## `[`
>> 
>> is.primitive(`[`)
>> ## [1] TRUE
>> 
>> is.primitive(mc[[1]])
>> ## [1] FALSE
>> # Expected to be TRUE
>> 
>> mc2 <- as.call(list(`[`,iris,2,"Species"))
>> 
>> is.primitive(mc2[[1]])
>> ## [1] TRUE
>> 
>> So depending on how I construct the call (using call() or as.call() ),
the
>> function `[` is or is not recognized as a primitive by is.primitive()
>> 
>> The behaviour is counterintuitive and -unless I miss something obvious
>> here- likely to be a bug imho. I immediately admit that my C chops
aren't
>> sufficient to come up with a patch.
>> 
>> Cheers
>> Joris
>> 
>> --
>> Joris Meys
>> Statistical consultant
>> 
>> Ghent University
>> Faculty of Bioscience Engineering
>> Department of Mathematical Modelling, Statistics and Bio-Informatics
>> 
>> tel :  +32 (0)9 264 61 79
>> Joris.Meys at Ugent.be
>> -------------------------------
>> Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php
>> 
>>        [[alternative HTML version deleted]]
>> 
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel