# @continuation vs callcc {} **URL:** \ **Category:** Ruby\ **Created:** [October 3, 2007, 10:53pm UTC](https://www.ruby-forum.com/t/continuation-vs-callcc/116260 "2007-10-03T22:53:44Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 3, 2007, 10:53pm UTC](https://www.ruby-forum.com/t/continuation-vs-callcc/116260/1 "2007-10-03T22:53:44Z")
[http://pastie.caboo.se/102022](http://pastie.caboo.se/102022) Greg Brown and I wrote this at Ruby East. It uses a continuation. The thing is, the purpose of this code is to allow you to pop out of irb into vi (or emacs, or TextMate, etc.) so you can edit your code, and then pop back into irb to evaluate it. We use a continuation because if there’s a syntax error in the code, you want to be able to get back to vi and rework the code without having to do a lot of work. The final version (or at least most up-to-date version) uses a different method. But the question here is - is this a real continuation? And also, we looked at switching it to use callcc(), but it looked like there wouldn’t be any real difference. What is the difference there? Would this code be better with callcc? – Giles B. Blog: [http://gilesbowkett.blogspot.com](http://gilesbowkett.blogspot.com) Portfolio: [http://www.gilesgoatboy.org](http://www.gilesgoatboy.org) Tumblelog: [http://giles.tumblr.com/](http://giles.tumblr.com/) ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 3, 2007, 11:38pm UTC](https://www.ruby-forum.com/t/continuation-vs-callcc/116260/2 "2007-10-03T23:38:55Z")
I don’t know you’re getting much benefit from the apparent contiuationess of this so much as the captured binding. I think you get the same effect from something like the following def bnd @b ||= binding end def vi system “vim #{file.path}” eval(file.read, bnd) end Some code ellided ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 4, 2007, 10:54am UTC](https://www.ruby-forum.com/t/continuation-vs-callcc/116260/3 "2007-10-04T10:54:11Z")
On 10/3/07, Logan C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > eval(file.read, bnd) > end Hmm Logan your solution does not seem to save state, I tried vi –\>@a=1 –\>:wq vi –\>p @a → :wq nil I have no clue where the problem is. To Giles: no this is not a continuation, I have however never been up to the task to understand continuations, so unfortunately I cannot really answer your questions. OTOH Why use the complicated stuff if the simple does? Or do you have a hidden agenda ;). There seems to be a problem with reopen too, I guess I fixed that, I have changed the name from @continuation to closure. What do you think about this version? ------------------------- 8\< ---------------------------- require ‘tempfile’ def closure file = Tempfile.new(“irb\_tempfile”) lambda do system(“vim #{file.path}”) eval(file.read) file.rewind end end def vi (@closure = closure).call rescue =\> error puts error end def reopen @closure.call if @closure rescue =\> error puts error end ------------------------- \>8 ---------------------------- Robert ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 4, 2007, 1:06pm UTC](https://www.ruby-forum.com/t/continuation-vs-callcc/116260/4 "2007-10-04T13:06:35Z")
On 10/4/07, Robert D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > system “vim #{file.path}” > > nil > > I have no clue where the problem is. Interesting. I’m a little surprised but not very surprised. I wasn’t sure if that would work, and at the time I had no ruby to test with. ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 4, 2007, 1:40pm UTC](https://www.ruby-forum.com/t/continuation-vs-callcc/116260/5 "2007-10-04T13:40:06Z")
On 10/4/07, Logan C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > def vi > > > → :wq > > > nil > > > > I have no clue where the problem is. > > Interesting. I’m a little surprised but not very surprised. I wasn’t > sure if that would work, and at the time I had no ruby to test with. Sorry Logan, I just fixed it, and when fixing it I found it strange and retested your solution, which … works perfectly! Need new glasses, sorry! Robert ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 4, 2007, 11:23pm UTC](https://www.ruby-forum.com/t/continuation-vs-callcc/116260/6 "2007-10-04T23:23:30Z")
On Oct 4, 2007, at 12:54 PM, Giles B. wrote: > I’m curious though about the difference between a continuation and a > proc you call manually when you want to continue with it. I had a book > somewhere that explained what callcc is really for, it showed how to > use call/cc in Lisp, I think Scheme, but I’m not sure where I left it. > Actually I think it was “The Scheme Programming Language.” "Continuations are the functional expression of the GOTO statement, and the same caveats apply.[citation needed] While many believe that they are a sensible option in some special cases such as web programming, use of continuations can result in code that is difficult to follow. In fact, the esoteric programming language Unlambda includes call-with-current-continuation as one of its features solely because of its resistance to understanding. The external links below illustrate the concept in more detail. > **[Continuation](https://en.wikipedia.org/wiki/Continuation)** > > In computer science, a continuation is an abstract representation of the control state of a computer program. A continuation implements (reifies) the program control state, i.e. the continuation is a data structure that represents the computational process at a given point in the process's execution; the created data structure can be accessed by the programming language, instead of being hidden in the runtime environment. Continuations are useful for encoding other control mechanisms in programmi... 😉 a @ [http://drawohara.com/](http://drawohara.com/) ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 4, 2007, 8:54pm UTC](https://www.ruby-forum.com/t/continuation-vs-callcc/116260/7 "2007-10-04T20:54:55Z")
> I don’t know you’re getting much benefit from the apparent > contiuationess of this so much as the captured binding. I think you > get the same effect from something like the following yeah, we were calling it a “poor man’s continuation” when we were hacking on it. it’s not really a continuation, yet it is a thing which allows you to continue. (so to speak.) > To Giles: no this is not a continuation, I have however never been up > to the task to understand continuations, so unfortunately I cannot > really answer your questions. > OTOH Why use the complicated stuff if the simple does? Or do you have > a hidden agenda ;). Actually I hacked on it some more and ended up with a much simpler version, no continuations or bindings, much easier to work with. [http://pastie.caboo.se/102939](http://pastie.caboo.se/102939) It just creates an object which stores stuff, basically. I’m curious though about the difference between a continuation and a proc you call manually when you want to continue with it. I had a book somewhere that explained what callcc is really for, it showed how to use call/cc in Lisp, I think Scheme, but I’m not sure where I left it. Actually I think it was “The Scheme Programming Language.” > ``` > eval(file.read) > > ``` > > def reopen > @closure.call if @closure > rescue =\> error > puts error > end I think the file.rewind might not be necessary any more. I think refactoring it into a method like that was a good idea. reopen was kind of a hack in the original, the more fully worked-out version will automatically reopen if you created a file (and will create different buffers if you use different editors, brag brag brag) but I think you could accomplish very much the same thing if you combine #vi and #reopen like this: def vi (@closure ||= closure).call rescue =\> error puts error end – Giles B. Blog: [http://gilesbowkett.blogspot.com](http://gilesbowkett.blogspot.com) Portfolio: [http://www.gilesgoatboy.org](http://www.gilesgoatboy.org) Tumblelog: [http://giles.tumblr.com/](http://giles.tumblr.com/) ---
**Author:** ![Giles\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/848f3c/32.png) [@Giles\_B](https://www.ruby-forum.com/u/Giles_B)\ **Post date:** [October 5, 2007, 9:42am UTC](https://www.ruby-forum.com/t/continuation-vs-callcc/116260/8 "2007-10-05T09:42:48Z")
On 10/4/07, Giles B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I think the file.rewind might not be necessary any more. > Hmm on my Linux it definitely was, did you test it on Windows? > rescue =\> error > puts error > end > Yup I just do not like instance variables 😉 (as one can see on my > Blog), I still had to use one as I was not capable of creating a > closure into the IRB session (that would be cool BTW). > And as I needed the rewind I had to complicate the code anyway ☹ > Robert