[Rd] `[` not recognized as a primitive in certain cases.

[Lukas Stadler]

“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
>> 
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>> 
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