[Rd] callCC in 2.7.0

[Gabor Grothendieck]

OK. Can you show code to implement the tail recursive version of
fib using callCC in R, say.

Here it is transformed to tail recursive style:

fib <- function(i, a = 0, b = 1) {
  if (i == 0) a else fib(i-1, b, a+b)

Now, how do I add callCC to all this so that the fib call
presumably does not create a new stack instance?

On Sun, Mar 30, 2008 at 1:31 PM, Luke Tierney <luke at stat.uiowa.edu> wrote:
> On Sun, 30 Mar 2008, Gabor Grothendieck wrote:
>
> > I think the only relationship to that is the name since
> > it does not appear to allow one to leave a function
> > in the middle of its processing and re-enter it back
> > at that point -- which is what would be needed.
>
> The article conflates basic CPS with having first class continuations
> as in Scheme. The discussion about compilers and tail calls only
> requires downward-only continuations of the kind provided by R's
> current callCC.  The user interface and coroutine discussion requires
> continuations that can be run outside of their creating context.  The
> most sophisticated variant, as provided in Scheme, also allows
> continuations to be run more than once.  I don't think any of the
> examples in the Wikipedia article need that, but there is some
> interesting work on using that to model web browsing behavior.
>
> At any rate, there is plenty of precedent for using callCC as the name
> for the construct here even when the continuation is no longer valid
> outside of the creating callCC call. So the relationship is more than
> just the name.
>
> luke
>
> >
> > On Sun, Mar 30, 2008 at 12:04 PM,  <h.wickham at gmail.com> wrote:
> >>
> >>> Would anyone like to explain if callCC in R 2.7.0 gives
> >>> anything that on.exit does not already provide?
> >>>
> >>> It seems that the exit condition once defined cannot
> >>> be added to overridden whereas with on.exit multiple
> >>> on.exit's add additional on.exits rather than being ignored.
> >>>
> >>> Is this important?
> >>
> >> It facilitates a completely different style of programming - see
> >> http://en.wikipedia.org/wiki/Continuation-passing_style
> >>
> >> --
> >> http://had.co.nz/
> >>
> >
>
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> >
>
> --
> Luke Tierney
> Chair, Statistics and Actuarial Science
> Ralph E. Wareham Professor of Mathematical Sciences
> University of Iowa                  Phone:             319-335-3386
> Department of Statistics and        Fax:               319-335-3017
>    Actuarial Science
> 241 Schaeffer Hall                  email:      luke at stat.uiowa.edu
> Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu
>