[R] An argument processing puzzle --- solution.

[Duncan Murdoch]

On 18/01/2010 7:51 PM, Rolf Turner wrote:
> Thanks to Berton Gunter and Peter Ehlers who both effectively solved
> my problem.  Prof. Gunter's solution, slightly more succinct, is:
> 
> foo <- function(x)
> {
>    if(is.name(sb <- substitute(x))) deparse(sb)
>     else eval(sb)
> }
> 
> (appropriately modified to fit into the ``mv()'' context.
> 
> Duncan Murdoch expressed the worry:
> 
>> How could you tell what a user intended who typed this?
>>
>> name1 <- "a"
>> name2 <- "b"
>> mv(name1, name2)
> 
> Well, I guess I couldn't.  I am not actually bothered by this
> however.  I only want mv() to work with the arguments being
> either names or expressions which evaluate to explicit text strings.

The ambiguity is that name1 and name2 are *both* expressions and names. 
  But as long as you are clear about which rule should apply in case of 
ambiguity, sounds like you've got what you need.

Duncan Murdoch


> What ***I*** would intend by mv(name1,name2) in those circumstances
> would be in effect:
> 
> 	name2 <- name1
> 	rm(name1)
> 
> I.e. I want mv() to apply to the objects ``name1'' and ``name2''.
> The fact that these objects consist of text strings which *could*
> name other objects is of no importance (to me).



> 
> Thanks again to all who responded.
> 
> 	cheers,
> 
> 		Rolf Turner
> 
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