[R] Evaluation of defaults in functions

[Gabor Grothendieck]

foo2 could be written:

   foo3 <- function(x, y = x) { force(y); x <- 0; y }

to make it clear that evaluation of y is being forced.  See ?force

On 9/28/06, Ulrich Keller <uhkeller at web.de> wrote:
> Hello,
>
> and sorry if this is already explained somewhere. I couldn't find anything.
>
> R (2.3.1, Windows) seems to perform some kind of lazy evaluation when
> evaluating defaults in function calls that, at least for me, leads to
> unexpected results. Consider the following, seemingly equivalent functions:
>
>  > foo1 <- function(x, y=x) {
> +   x <- 0
> +   y
> + }
>  > foo1(1)
> [1] 0
>  > foo2 <- function(x, y=x) {
> +   y <- y
> +   x <- 0
> +   y
> + }
>  > foo2(1)
> [1] 1
>
> Obviously, y is not evaluated until it is used in some way. I would
> expect it to be evaluated where it is defined. Is this intended behavior?
> Thanks for clarifying,
>
> Uli
>
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