[Rd] On the mechanics of function evaluation and argument matching

[Ben Bolker]

Brian Rowe <rowe <at> muxspace.com> writes:

> 
> Thanks for the lead. Given the example in ?missing though,
>  wouldn't it be safer to explicitly define a
> default value of NULL:
> 
> myplot <- function(x, y=NULL) {
>   if(is.null(y)) {
>     y <- x
>     x <- 1:length(y)
>   }
>   plot(x, y)
> }
> 

 [snip]

 In my opinion the missing() functionality can indeed be
fragile (for example, I don't know how I can manipulate an
existing call to make an argument be 'missing' when it was
previously 'non-empty') and using an explicit NULL is often
a good idea.  This makes the documentation a tiny bit less
wieldy if you have lots of parameters ...