Laurent and Robert, Thank you all.
On Thu, Dec 16, 2010 at 9:44 AM, Laurent PETIT <laurent.pe...@gmail.com>wrote: > Indeed ! > > I was stuck in the macro thinking, thanks for getting us out of it ! > > And then this solution not only works for literal strings: > > user=> (foo (str "yo" "man")) > #'user/yoman > user=> yoman > "yoman" > user=> > > 2010/12/16 Robert McIntyre <r...@mit.edu> > > no need to use macros at all: >> >> (defn foo >> "creates a symbol named s with the value s in the current namespace " >> [s] >> (intern *ns* (symbol s) s)) >> >> that is, assuming I got the use case right. >> >> --Robert McIntyre >> >> >> On Wed, Dec 15, 2010 at 8:00 AM, Laurent PETIT <laurent.pe...@gmail.com> >> wrote: >> > 2010/12/15 Emeka <emekami...@gmail.com> >> >> >> >> Helllo All, >> >> Is there a better way of doing this? >> >> (defmacro foo [string] (let[b# string f# (symbol b#)] `(def ~f# ~b#))) >> > >> > Hello, >> > >> > What is it supposed to be used ? >> > >> > What do you expect the macroexpansion to look like ? >> > >> > As is stands, your example can go without the ending #'s since they >> aren't >> > declared inside the returned quoted expr. They're useless. >> > >> > So having >> > >> > (defmacro foo [string] (let [b string f (symbol string)] `(def ~f ~b))) >> > >> > But now, string is not (as you may think) evaluated within the let in >> the >> > macro. string is just an immutable datastructure containing "as is" what >> has >> > been passed to foo. So if what you pass to foo is something which >> > "evaluates" to a string, for example a string concatenation expression >> as >> > (str "the-" "value"), then the code will not do what it suggests it's >> doing >> > : >> > >> > user=> (defmacro foo [string] (let[b# string f# (symbol b#)] `(def ~f# >> > ~b#))) >> > #'user/foo >> > user=> (foo (str "the-" "value")) >> > java.lang.ClassCastException: clojure.lang.PersistentList cannot be cast >> to >> > java.lang.String (NO_SOURCE_FILE:0) >> > user=> (macroexpand '(foo (str "the-" "value"))) >> > java.lang.ClassCastException: clojure.lang.PersistentList cannot be cast >> to >> > java.lang.String (NO_SOURCE_FILE:0) >> > user=> >> > >> > >> > Now, if you just want the macro to take literal strings as input, then >> the >> > code can be further simplified to : >> > >> > (defmacro foo [string] `(def ~(symbol string) ~string)) >> > >> > user=> (defmacro foo [string] `(def ~(symbol string) ~string)) >> > #'user/foo >> > user=> (foo "the-string") >> > #'user/the-string >> > user=> the-string >> > "the-string" >> > user=> (macroexpand '(foo "the-string")) >> > (def the-string "the-string") >> > user=> >> > >> > HTH, >> > >> > -- >> > Laurent >> > >> > -- >> > 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<clojure%2bunsubscr...@googlegroups.com> >> > For more options, visit this group at >> > http://groups.google.com/group/clojure?hl=en >> >> -- >> 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<clojure%2bunsubscr...@googlegroups.com> >> For more options, visit this group at >> http://groups.google.com/group/clojure?hl=en >> > > -- > 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<clojure%2bunsubscr...@googlegroups.com> > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > -- *Satajanus Nig. Ltd * -- 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
