How to make a function aware of its own call arguments

On 24/03/2016 10:28 AM, sbihorel wrote:

Hi,

Thanks for your suggestion.

missing(x) works only if x is not altered within the function, which is
not the case in my actual function (which is more complex than the
example function I send in my previous post).

That's not quite true:  missing(x) works *before* x is altered within 
the function.  It works even if x has a default value.

So your myf2 could just use missing(c):

myf2 <- function(a=1, b=2, fun=NULL, c=myfun1(b,fun)){

   if (myf1(b,fun)>0 && missing(c)){
     c <- b
   }
   print(list(a,b,c))
}

Are you aware of any function what would query the original function
call arguments no matter what happens in the function?

The match.call() function does that, but I think you don't need that:

f <- function(x = 1, ...) {
  x <- 2
  match.call()
}
f(3)
## Prints:  f(x = 3)

Duncan Murdoch

Sebastien

On 3/24/2016 8:47 AM, Jeff Newmiller wrote:

Don't provide a default value for c in the parameter list. Then you
can use the missing() function to make decisions, including whether to
generate a default value for c or not.
--
Sent from my phone. Please excuse my brevity.

On March 24, 2016 5:11:43 AM PDT, sbihorel
<Sebastien.Bihorel at cognigencorp.com> wrote:

    Hi,

    Please consider the following functions:

    myf1 <- function(x,fun){
        if (is.null(fun)){
          x
        } else {
          do.call(fun, list(x))
        }
    }

    myf2 <- function(a=1, b=2, fun=NULL, c=myfun1(b,fun)){

        if (myf1(b,fun)>0 & <c was not provided in function call>){
          c <- b
        }
        print(list(a,b,c))
    }

    myf2(a=2,b=3,fun=exp)
    myf2(a=2,b=3,fun=exp,c=4)

    I need to replace "<c was not provided in function call>" by 

some code

    that would make myf2 aware of it own calls and of the fact that 

the c

    argument was provided or not in the function calls.

    Thanks for your help

    Sebastien

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