Here's a reason why a partial application macro is better than a partial application function:
user=> ((partial or (prn "Hello")) (prn "World")) java.lang.Exception: Can't take value of a macro: #'clojure.core/or (NO_SOURCE_FILE:2) user=> (($ or (prn "Hello")) (prn "World")) "World" "Hello" nil user=> (or (prn "Hello") (prn "World")) "Hello" "World" nil This shows what I mean about evaluation: the parameter (prn "World") gets evaluated before (prn "Hello"), so the messages get sent in a different order than if you had not used partial application. I tried to figure out a way for a macro to return a macro, to try to further delay the evaluation of the non-partially-applied parameters, but couldn't figure out a way to do it. Thanks for showing me the auto-gensym facility. I couldn't look up the documentation when I wrote this because my internet was out. All I had to consort me was core.clj. On May 28, 1:22 am, Laurent PETIT <laurent.pe...@gmail.com> wrote: > Here is a somewhat simpler definition :-) : > > user=> (def $ clojure.core/partial) > #'user/$ > user=> (def add5 ($ + 5)) > #'user/add5 > user=> (add5 3) > 8 > user=> > > But maybe you want the delayed evaluation of the already included > arguments, but it is not clear to me from your e-mail (and your > example that uses a literal integer), and it's also not clear to me > what uses cases may require this macro. Could you elaborate a little > more on the subject ? > > Please also note the gensym facility of clojure (get rid of the > gensym, and autocreate a gensym by suffixing a # to a symbol inside a > syntax quote expression) : > > (defmacro $ [f & args] > `(fn [& args2#] > (eval (cons (quote ~f) (concat (quote ~args) args2#))))) > > See: > user=> (macroexpand `(args2# args2#)) > (args2__44__auto__ args2__44__auto__) > user=> > > Regards, > > -- > Laurent > > 2009/5/28 kinghajj <kingh...@gmail.com>: > > > > > (defmacro $ [f & args] > > (let [args2 (gensym)] > > `(fn [& ~args2] > > (eval (cons (quote ~f) (concat (quote ~args) ~args2)))))) > > > Example: > > (def add5 ($ + 5)) > > > (add5 3) > > > Beware! For this macro evaluates the later parameters before the > > partially-applied ones, so side-effectful parameters may occur in an > > unexpected order. > > --~--~---------~--~----~------------~-------~--~----~ 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 clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
