On Jul 27, 9:23 pm, Alan Malloy <a...@malloys.org> wrote: > On Jul 27, 11:56 am, Dmitry Gutov <raa...@gmail.com> wrote: > > > > First: Why doesn't macroexpand expand the inner when-lets? > > > It's not supposed to, see the doc. To do full expansion, you can use > > `clojure.walk/macroexpand-all`. > > > > Is the gensym in the two expands the same thing, or do "they" get the > > > same name? That was surprising to me. I can't think of any real > > > example where that is a problem. But what if I had wanted to write a > > > macro like the second when-lets? > > > Looks like a bug/limitation of the gensym reader macro, these symbols > > are treated as belonging to the same quoted form, so they get the same > > name. >
> Nothing to do with being the same quoted form: foo# symbols are > gensymmed at read time, so by the time the macro runs there's no > evidence that they were ever gensyms: just a symbol named > temp__1551__auto__, and it has no reason to suppose you intend them to > be different. > > I don't think this is a problem for many (any?) macros, but if you > want more control you can gensym yourself: Right! Thanks! > > (defmacro when-lets > [bindings & body] > (if-not (seq bindings) > `(do ~@body) > (let [temp (gensym) form (bindings 0) tst (bindings 1) rst (drop 2 > bindings)] > `(let [~temp ~tst] > (when ~temp > (when-lets ~(vec rst) > (let [~form ~temp] > ~@body))))))) > > user> (use 'clojure.walk) (macroexpand-all '(when-lets [a 1 b 2] [a > b])) > (let* [G__1815 1] (if G__1815 (do (let* [G__1816 2] (if G__1816 (do > (do (let* [b G__1816] (let* [a G__1815] [a b]))))))))) > > user> (when-lets [a 1 b 2] [a b]) > [1 2] -- 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
