Thanks everyone! I certainly have my solution; but, I'm still a bit confused. Here's another example...
user=> (defmacro foo [coll] `(map identity ~coll)) #'user/foo user=> (foo (list 1 2 3)) (1 2 3) In this example, I pass an explicit list and all I have to do is unquote 'coll'. How is passing an explicit list any different than having it destructured via '&' in the argument vector? On Jul 7, 1:11 pm, Jason Wolfe <jawo...@berkeley.edu> wrote: > Hi Cameron, > > On Jul 7, 9:49 am, Cameron <cpuls...@gmail.com> wrote: > > > Hello all! Today, I've either discovered a bug, or I've discovered a > > flaw in my understanding of macros. Most likely the latter :-) Could > > anyone set me straight? > > > While this is not the macro I was trying to write, it falls over in > > the same place. > > > (user=> (defmacro foo [& xs] `(map identity ~xs)) > > #'user/foo > > user=> (foo 1 2) > > java.lang.ClassCastException: java.lang.Integer cannot be cast to > > clojure.lang.IFn (NO_SOURCE_FILE:0) > > Well, let's look at the macroexpansion: > > user> (macroexpand '(foo 1 2)) > (clojure.core/map clojure.core/identity (1 2)) > > As you can see, this tries to call 1 with an argument of 2, which > gives the exception you see. > > If you want your arguments evaluated, I think your solution is as good > as any. If you want them unevaluated, you can do: > > user> (defmacro foo2 [& xs] `(map identity '~xs)) > #'user/foo2 > user> (foo2 1 2) > (1 2) > > The difference: > > user> (foo2 1 (+ 1 1)) > (1 (+ 1 1)) > > -Jason -- 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
