I agree that #:while and #:until are easily confused with #:when and #:unless. I slightly prefer #:stop- to #:break- as a prefix here, it seems a more natural word. I like the idea of allowing these clauses at the end of the body to give a notion of stopping after the current iteration. I had been wondering how to do that, and hadn't come up with anything nearly so simple. On Fri, Sep 14, 2012 at 11:40 AM, Matthew Flatt <<a href="mailto:mflatt@cs.utah.edu" target="_blank">mflatt@cs.utah.edu</a>> wrote: <div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> I think this is a good idea. The technique to implement it is embedded in `for/vector' (to handle a vector length), and I can generalize that and move it into `for...'. Also, I think the names `#:while' and `#:until' are too close to `#:when' and `#:unless'. I suggest `#:break-when' and `#:break-unless'. Compare: > (for*/list ([j 2] [i 10] #:when (i . < . 5)) i) '(0 1 2 3 4 0 1 2 3 4) > (for*/list ([j 2] [i 10] #:break-unless (i . < . 5)) i) '(0 1 2 3 4) I imagine that `#:break-when' and `#:break-unless' are allowed among the clauses much like `#:when' and `#:unless', but also allowed at the end of the body. Is that what you had in mind? <div><div class="h5"> At Fri, 14 Sep 2012 10:09:52 -0400, Carl Eastlund wrote: > I would like the for/... comprehension macros to have #:while and #:until > clauses similar to the #:when and #:unless clauses. I often find I want to > short-circuit the sequence at some point, but there is no elegant way to do > it. I could probably write sequence-while and sequence-until, but I don't > want to move this condition into the sequence any more than I want to write > sequence-filter instead of #:when or #:unless. > > Has this been brought up before? I can't recall. Does anyone else run > into the same issue? > > Carl Eastlund </div></div>> _________________________ > Racket Developers list: > <a href="http://lists.racket-lang.org/dev" target="_blank">http://lists.racket-lang.org/dev</a> </blockquote></div>