Warning when calling formals() for `[`.

Hello,

I believe that this is maybe not a *feature* but at least expected 
behaviour.

The call formals(args(`[`)) breaks down to

 > args(`[`)

NULL

 > formals(NULL)

NULL
Warning message:
In formals(fun) : argument is not a function


Hope this helps,

Rui Barradas


?s 18:26 de 06/10/2018, Laurent Gautier escreveu:

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

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