R help - May 2010 - Lazy evaluation in function call

Hi everybody,

how is it possible to refer to an argument passed to a function in the 
function call? What I like to do, is something like

f <- function(x,y) x+y
f(2, x) # should give 4

The problem is of course that x is only known inside the function. Of course I 
could specify something like

f(z<-2,z)

but I'm just curious whether it is possible to use a fancy combination of 
eval, substitute or quote ;)

BR, thorn

I think you'll have to code it a bit different. I'd do :
f <- function(x,y){
if(missing(y)) y <-x
x+y
}
> f(2)
[1] 4
> f(2,3)
[1] 5
>
On Tue, May 4, 2010 at 4:26 PM, Thorn <thorn.thaler@rdls.nestle.com>
wrote:
> Hi everybody,
>
> how is it possible to refer to an argument passed to a function in the
> function call? What I like to do, is something like
>
> f <- function(x,y) x+y
> f(2, x) # should give 4
>
> The problem is of course that x is only known inside the function. Of
> course I
> could specify something like
>
> f(z<-2,z)
>
> but I'm just curious whether it is possible to use a fancy combination
of
> eval, substitute or quote ;)
>
> BR, thorn
>
> ______________________________________________
> R-help@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.
>


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