[R] return from nested function?

[Duncan Murdoch]

On Wed, 2 Mar 2005 12:13:17 +0000, "Jan T. Kim" <jtk at cmp.uea.ac.uk>
wrote :

>On Tue, Mar 01, 2005 at 11:21:44PM -0800, Seth Falcon wrote:
>> On Feb 25, 2005, at 12:34 PM, jhallman at frb.gov wrote:
>> 
>> >Is is possible from within a function to cause its caller to return()?
>> 
>> This snippet may be of interest:
>> 
>> 
>> > f = function(x) {
>> + print("f")
>> + g(return())
>> + print("end of f")
>> + }
>> 
>> > g=function(x) {print("g")
>> + x
>> + print("end of g")
>> + }
>> 
>> > f(1)
>> [1] "f"
>> [1] "g"
>> NULL
>
>I may be dumb today, but doesn't that beg the question of how does g
>cause f not to return?

I'm not suggesting that I would ever use code like this, but if x is
never evaluated then the double return would not happen:

> f
function(x) {
print("f")
g(x, return())
print("end of f")
}
> g
function(x, blastoff) {
   print("g")
   if (x) blastoff
   print("end of g")
}
> f(TRUE)
[1] "f"
[1] "g"
NULL
> f(FALSE)
[1] "f"
[1] "g"
[1] "end of g"
[1] "end of f"

However, this is not a style of programming that I would expect to
last for more than 5 minutes after I published a program using it.
Follow Thomas's advice, and use tryCatch instead.

Duncan Murdoch