@Phlex, I understand why the code is usually bad form. @MikeM, I had already noticed that it worked on the REPL when I defined vars. My questions was _why_ it does not work in the case where I have locals via a let expression?
David On Mon, Nov 3, 2008 at 12:27 PM, MikeM <[EMAIL PROTECTED]>wrote: > > > > On Nov 3, 9:57 am, David Nolen <[EMAIL PROTECTED]> wrote: > > (defmacro foobar [] > > `'(+ a b)) > > > > (let > > [a 5 > > b 6] > > (eval (foobar))) > > > > I know that the above is completely useless but I'm just trying to get > > an intuitive understanding of how macros work under Clojure. At the > > REPL when I try to evaluate the second form, I get an null pointer > > exception. Why can't the result of the foobar macro access the values > > of a and b? > > > > If you macroexpand, > > >(macroexpand '(foobar)) > > you'll see that the a and b symbols in your macro are resolved to be > vars in the namespace in which the macro is defined (I defined the > macro in the user namespace): > > (quote (clojure/+ user/a user/b)) > > Note that symbol + was resolved to be the + function from boot.clj, > since my user namespace refers to the clojure namespace. > > So when the foobar macro is run, the resulting code doesn't look at > the a and b in your let, but instead tries to find vars named a and b. > If you: > > > (def a 1) > > (def b 2) > > then execute > > > (let > > [a 5 > > b 6] > > (eval (foobar))) > > you'll get 3. > > Hope that helps. > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
