R help - May 2011 - calling "exists" function inside another function is not working

Hi all,
   I want to define a function such that one of its argument if passed do one
   thing and if not passed do the second thing. So basically, I have to check
   whether the argument is passed or not inside the function. I am trying to
   use 'exists' function to do this.
   > f = function(a,b){exists("b")}
   > f(a=3, b=4)
   [1] TRUE
   This is working as expected.
   But if I do the following:
   > f(a=3)
   [1] TRUE
   Can anybody explain why this function is returning TRUE here.
-- 
Many thanks,
Utkarsh

On May 14, 2011, at 3:30 AM, utkarshsinghal wrote:
>
>   Hi all,
>   I want to define a function such that one of its argument if  
> passed do one
>   thing and if not passed do the second thing.
?missing
> So basically, I have to check
>   whether the argument is passed or not inside the function. I am  
> trying to
>   use 'exists' function to do this.
>> f = function(a,b){exists("b")}
>> f(a=3, b=4)
>   [1] TRUE
>   This is working as expected.
>   But if I do the following:
>> f(a=3)
>   [1] TRUE
>   Can anybody explain why this function is returning TRUE here.
> -- 
> Many thanks,
> Utkarsh
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT

Might it be feasible to add, "See Also:  missing" to the help 
page for "exists"?


       Currently, one can spend hours studying the help page for 
"exists" without getting a clue to the answer to the post copied
below.


       Thanks,
       Spencer


On 5/14/2011 3:30 AM, David Winsemius wrote:
>
> On May 14, 2011, at 3:30 AM, utkarshsinghal wrote:
>
>>
>>   Hi all,
>>   I want to define a function such that one of its argument if passed 
>> do one
>>   thing and if not passed do the second thing.
>
> ?missing
>
>> So basically, I have to check
>>   whether the argument is passed or not inside the function. I am 
>> trying to
>>   use 'exists' function to do this.
>>> f = function(a,b){exists("b")}
>>> f(a=3, b=4)
>>   [1] TRUE
>>   This is working as expected.
>>   But if I do the following:
>>> f(a=3)
>>   [1] TRUE
>>   Can anybody explain why this function is returning TRUE here.
>> -- 
>> Many thanks,
>> Utkarsh
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide 
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> West Hartford, CT
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>