From lawrence.michael at gene.com  Tue Mar 28 14:46:56 2017
From: lawrence.michael at gene.com (Michael Lawrence)
Date: Tue, 28 Mar 2017 05:46:56 -0700
Subject: [Rd] `[` not recognized as a primitive in certain cases.
In-Reply-To: <CAO1zAVYLbF9fo8VxO8NKVYvS2yr=GDa3YrO+se8y5bq4QFUr4A@mail.gmail.com>
References: <CAO1zAVYLbF9fo8VxO8NKVYvS2yr=GDa3YrO+se8y5bq4QFUr4A@mail.gmail.com>
Message-ID: <CAOQ5NyfDoxZ-8Ga+WfHSBqnutsvN+=FNYJxgGM1hfNWn3UkWwQ@mail.gmail.com>

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
> -------------------------------
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[Rd] `[` not recognized as a primitive in certain cases.
Michael Lawrence