[Rd] buglet in is.na?

[Peter Dalgaard]

Nicholas Lewin-Koh wrote:
> Hi
> the following example I think demonstrates the inconsistency
>> f<-function(x) x
>> length(f)
> [1] 1
>> is.na(f)
> [1] FALSE
> Warning message:
> In is.na(f) : is.na() applied to non-(list or vector) of type 'closure'
> 
> The documentation states:
> Arguments
> x       an R object to be tested.
> value   a suitable index vector for use with x.
> 
> And nowhere in the details was it implied (to me anyway) that x could
> not be a function
> or anything else in R for that matter. Did I miss something?
> 

Well, it's just a warning which you get whenever you apply is.na to 
things that cannot logically be NA, e.g.

 > is.na(.GlobalEnv)
[1] FALSE FALSE
Warning message:
In is.na(.GlobalEnv) :
   is.na() applied to non-(list or vector) of type 'environment'
 > is.na(quote(a))
[1] FALSE
Warning message:
In is.na(quote(a)) :
   is.na() applied to non-(list or vector) of type 'symbol'
 > is.na(quote(`NA`))
[1] FALSE
Warning message:
In is.na(quote(`NA`)) :
   is.na() applied to non-(list or vector) of type 'symbol'
 > is.na(is.na)
[1] FALSE
Warning message:
In is.na(is.na) : is.na() applied to non-(list or vector) of type 'builtin'

I suppose the documentation could be more explicit about it, but where's 
the need?

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