On Fri, Nov 14, 2008 at 10:51 PM, Bradbev <[EMAIL PROTECTED]> wrote: > > I thought up an interesting issue the other night. If you map a > function over a seq of refs, then change the refs & look at the map > return value (which will convert it from lazy to ...? Hmm, what's the > word - motivated?) then you will get the current value of the refs. > > The example code is > (def refs (into [] (map #(ref %) (range 10)))) > (def dref (map deref refs)) > > (doseq r refs > (dosync > (commute r #(* 2 %)))) > > (println dref) > > When you consider how map works, this actually makes total sense. > However, I think that it is something of a gotcha. > Normally you don't need to know that map returns a lazy seq, because > normally you would be mapping over immutable data. But if you happen > to map over seqs that have refs, then you might have problems. I find > it conceptually jarring - normally laziness is a transparent > abstraction. > > I guess the main reason I'm posting this is to point out the issue. I > wonder if this gotcha should be highlighted somewhere in the official > documentation, or am I making a mountain out of a molehill?
The seq documentation says this: "Robust programs should not mutate arrays or Iterables that have seqs on them." Perhaps something similar should be mentioned on the data structures page? -- Michael Wood <[EMAIL PROTECTED]> --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
