[Rd] Warning when calling formals() for `[`.

[Peter Dalgaard]

> On 7 Oct 2018, at 16:04 , Rui Barradas <ruipbarradas using sapo.pt> wrote:
> 
> Hello,
> 
> I don't see why you say that the documentation seems to be wrong:
> 
> 
> class(args(`+`))
> #[1] "function"
> 
> 
> args() on a primitive does return a closure. At least in this case it does.

But in this case it doesn't:

> is.primitive(get("["))
[1] TRUE
> class(args(get("[")))
[1] "NULL"

Or, for that matter:

> is.primitive(`[`)
[1] TRUE
> class(args(`[`))
[1] "NULL"

-pd

> 
> 
> Rui Barradas
> 
> Às 14:05 de 07/10/2018, Peter Dalgaard escreveu:
>> There is more "fun" afoot here, but I don't recall what the point may be:
>>> args(get("+"))
>> function (e1, e2)
>> NULL
>>> args(get("["))
>> NULL
>>> get("[")
>> .Primitive("[")
>>> get("+")
>> function (e1, e2)  .Primitive("+")
>> The other index operators, "[[", "[<-", "[[<-" are similar
>> The docs are pretty clear that args() on a primitive should yield a closure, so at least the documentation seems to be wrong.
>> -pd
>>> On 6 Oct 2018, at 19:26 , Laurent Gautier <lgautier using gmail.com> wrote:
>>> 
>>> Hi,
>>> 
>>> A short code example showing the warning might the only thing needed here:
>>> 
>>> ```
>>>> formals(args(`[`))
>>> NULL
>>> 
>>> *Warning message:In formals(fun) : argument is not a function*
>>>> is.function(`[`)
>>> [1] TRUE
>>>> is.primitive(`[`)
>>> [1] TRUE
>>> ```
>>> 
>>> Now with an other primitive:
>>> 
>>> ```
>>>> formals(args(`sum`))
>>> $...
>>> 
>>> 
>>> $na.rm
>>> [1] FALSE
>>> 
>>>> is.function(`sum`)
>>> [1] TRUE
>>>> is.primitive(`sum`)
>>> [1] TRUE
>>>> class(`[`)
>>> [1] "function"
>>> ```
>>> 
>>> Is this a feature ?
>>> 
>>> 
>>> Laurent
>>> 
>>> 	[[alternative HTML version deleted]]
>>> 
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-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
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