(defmacro choose [[c choices] & body] `(choose* (fn [~c] ~@body) ~choices)) <--- not ~@, just ~
~@ expects a sequence result In your first example, [:a :b :c] is a sequence but in the second example, y is not. body is a sequence (& body), using ~@ there is ok there. Luc P. On Wed, 13 Jul 2011 07:33:57 -0700 (PDT) Andrea Tortorella <elian...@gmail.com> wrote: > I'm not an expert in macros, and maybe this is a stupid question but i > think there should be a general pattern for this. > > I' ve a function: > > (defn choose* [f & choices] > "Applies f to one of the choices" > ..... .....) > > And this macro: > > (defmacro choose [[c choices] & body] > `(choose* (fn [~c] ~@body) ~@choices)) > > Now if i call it with a literal sequence: > > (choose [x [:a :b :c]] > (println x)) > > it correctly expands to: > > (choose* (fn [x] (println x)) :a :b :c) > > but if i have: > > (def y [:a :b :c]) > (choose [x y] > (println x)) > > it gives me an error: don't know how to create ISeq from symbol. > > with an expression: > > (choose [x (vec 2 3 4)] > (println x)) > > it expands to: > > (choose* (fn [x] (println x)) vec 2 3 4) > > I knew it could not be that simple, and i also understand why i get > theese expansions, but i don't get how to solve it. > So what's the pattern for something like this, where you want to > evaluate a symbol or an expression before expansion? > > Andrea > -- Luc P. ================ The rabid Muppet -- 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
