OK. Perfect. Thanks. I was worried there for a moment. Next time I'll read the docs more carefully. My fault.
On Jan 13, 3:29 am, Rich Hickey <richhic...@gmail.com> wrote: > On Jan 12, 6:49 pm, Rock <rocco.ro...@gmail.com> wrote: > > > > > After a fair amount of macro writing in CL, I think I got the > > backquote expansion mechanism pretty much nailed down (after all, it > > is quite clear in the HyperSpec). Now, I thought I understood the > > Clojure algorithm just as well. It looked very similar (concat instead > > of append and so on). Apart from the namespace resolution business, > > and a few other irrelevant details, the essence looked the same. > > > But I did the following just for fun, and I got a surprising result: > > > > (def x `a) > > > (def a 5) > > > `(list `(list ,,x)) > > > What I theoretically was expecting was the outcome of this: > > > (concat (list `list) (list (concat (list `concat) (list (concat (list > > `list) (list ``list))) (list (concat (list `list) (list x)))))) > > > In other words, behind the curtains, the latter was supposed to be > > evaluated. Now, as Guy Steele points out, with a k-level nested > > backquote, you are guaranteed to get the same result only after k > > evaluations. So evaluating twice the result is: > > > ((clojure.core/list 5)) > > > I checked this in Common Lisp and the result was sure enough exactly > > the equivalent, as I expected. > > > Yet, in clojure this is what happens (of course you see the first > > evaluation directly in this case): > > > > `(list `(list ,,x)) > > > (clojure.core/list (clojure.core/concat (clojure.core/list (quote > > clojure.core/list)) (clojure.core/list (quote user/x)))) > > > Another evaluation gives: > > ((clojure.core/list user/x)) > > > That's ALMOST the same but not quite. See the "user/x"? It came from a > > very strange (quote user/x) above which wasn't supposed to be there. I > > mean user/x should not have been quoted. > > > Is this a bug? > > The unquote character in Clojure is ~ not comma. > > user=> (eval `(list `(list ~~x))) > ((clojure.core/list 5)) > > Rich --~--~---------~--~----~------------~-------~--~----~ 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 clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
