Yes, definitely. Your version selects which form to evaluated once, at compile time; the original selects a form every time the expansion is evaluated.
user> (defn rand-num [] (rand-expr-mulit 1 2 3 4 5 6 7 8 9)) #'user/rand-num user> (rand-num) 7 user> (rand-num) 7 user> (rand-num) 7 user> (rand-num) 7 Instead, you need to make sure the call to rand-int is in the code you return, rather than in the logic the macro uses to decide what code to return. On Oct 24, 12:17 pm, Alan O'Donnell <alan.m.odonn...@gmail.com> wrote: > Hi everyone, > > I'm working my way through Practical Clojure's macro chapter, and I'd like > to check my understanding about one of the examples. > > The book discusses writing a macro to randomly evaluate a form out of a list > of forms--essentially a cond that randomly selects which branch to evaluate. > > The book's version looks like this: > > (defmacro rand-expr-multi [& exprs] > > `(let [ct# ~(count exprs)] > > (case (rand-int ct#) > > ~@(interleave (range (count exprs)) exprs)))) > > My version looks like this: > > (defmacro rand-expr-mulit [& exprs] > > (let [n (rand-int (count exprs))] > > (nth exprs n))) > > Is there any difference between the two? I'm a little shaky on macro > expansion-time vs run-time, hygiene, etc. -- 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 Note that posts from new members are moderated - please be patient with your first post. 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
