R help - Jul 2010 - Documentation for library() and how to specify missing arguments

I can, after carefully reading about the returned values, see why

library("MASS", "MASS", character.only=TRUE)

has to chose between loading the package and displaying the help (I 
thought I had found a nice shortcut), but wouldn't the documentation be 
better if it said that the two are incompatible and that package= takes 
precedence over help=?


As an aside, is there a way to explicitly specify a missing argument in 
a function call?  For an example using the same function as before,

library(, "MASS", character.only=TRUE)

displays the help but can be a little hard on the programmer's eyes.  
However,

library(NULL, "MASS", character.only=TRUE)
library(NA, "MASS", character.only=TRUE)
library({}, "MASS", character.only=TRUE)  #  signals error.

doesn't do the same at all (I thought the first one would, based on the 
"whenever" in the documentation: "It is used whenever there is a
need to
indicate or specify that an object is absent.").

Is there in the language a lexical x such that f(x, ...) is the same as 
f(, ...)?

(Yes, I know about named arguments and I like them, I am just trying to 
learn syntax here.)

Allan

On Jul 1, 2010, at 1:24 PM, Allan Engelhardt wrote:
> I can, after carefully reading about the returned values, see why
>
> library("MASS", "MASS", character.only=TRUE)
>
> has to chose between loading the package and displaying the help (I  
> thought I had found a nice shortcut), but wouldn't the documentation  
> be better if it said that the two are incompatible and that package=  
> takes precedence over help=?
>
>
> As an aside, is there a way to explicitly specify a missing argument  
> in a function call?  For an example using the same function as before,
>
> library(, "MASS", character.only=TRUE)
I have always used:

help(package=MASS)   # does not need to be quoted

My annoyance/whine is that various functions use "pkg", pkgs", or
"package" as argument names. This is the only one I have successfully
committed to memory.

>
> displays the help but can be a little hard on the programmer's  
> eyes.  However,
>
> library(NULL, "MASS", character.only=TRUE)
> library(NA, "MASS", character.only=TRUE)
> library({}, "MASS", character.only=TRUE)  #  signals error.
>
> doesn't do the same at all (I thought the first one would, based on  
> the "whenever" in the documentation: "It is used whenever
there is a
> need to indicate or specify that an object is absent.").
>
> Is there in the language a lexical x such that f(x, ...) is the same  
> as f(, ...)?
>
> (Yes, I know about named arguments and I like them, I am just trying  
> to learn syntax here.)
>
> Allan
-- 

David Winsemius, MD
West Hartford, CT

On Thu, Jul 1, 2010 at 1:24 PM, Allan Engelhardt <allane at cybaea.com>
wrote:
>
> Is there in the language a lexical x such that f(x, ...) is the same as f(,
> ...)?
>
Try this:
> mx <- formals(identity)$x
> missing(mx)
[1] TRUE
> sin(mx)
Error in sin(mx) : 'mx' is missing