Thanks everyone for the useful feedback. I'll check out all three options. :-) <div class="gmail_quote">On Fri, Mar 22, 2013 at 12:23 PM, Pierpaolo Bernardi <<a href="mailto:olopierpa@gmail.com" target="_blank">olopierpa@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5">On Thu, Mar 21, 2013 at 11:55 PM, Tim Nelson <<a href="mailto:tbnelson@gmail.com">tbnelson@gmail.com</a>> wrote: > Dear All, > > I've recently started hacking Racket again, and am loving the for/* > constructs. > Awesome stuff. However, I have two questions about for/hash. > > (1) How can I *not* add a hash entry for a given iteration? > > When I use for/list, can I abuse the nature of empty and append* (I cringe > as I write this): > > (append* (for/list ([i '(1 2 3 4 5)]) > (cond [(even? i) (list (* i 100))] > [else empty]))) > > Surely there is a better way to do this for for/list, and a way in general > for for/hash? > > (2) How can I add multiple entries (that is, >1 key-value pair) in a given > iteration? > > Again, using for/list I can cheat via append*: > > (append* (for/list ([i '(1 2 3 4 5)]) > (list (* i 100) (* i 200)))) > > What's the right way to do this in for/hash? </div></div>To both of the questions, the answer is for/fold! Cheers P. </blockquote></div>