[R] Testing for existence inside a function

[Talbot Katz]

Hi.

I'm having trouble testing for existence of an object inside a function.

Suppose I have a function:

f<-function(x){
...
}

and I call it with argument y:

f(y)

I'd like to check inside the function whether argument y exists.  Is this 
possible, or do I have to either check outside the function or pass the name 
of the argument as a separate argument?

If I do exists(x)  or exists(eval(x)) inside the function and y does not 
exist, it generates an error message.  If I do exists("x") it says that x 
exists even if y does not.  If I had a separate argument to hold the text 
string "y" then I could check that.  But is it possible to check the 
existence of the argument inside the function without passing its name as a 
separate argument?

Thanks!

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