The second edition of Joy of Clojure, MEAP v10 shows the same error and progressive solution about half way down pdf-page 318 in section 9.2.4.
On Monday, May 19, 2014 6:39:26 AM UTC-7, gamma235 wrote: > > Hi guys, I am working through the pre-release second edition of Joy of > Clojure's section on multi-methods (section 9.2.~ : pg. 313), and am > getting different outputs from what they have printed in the book. I could > just skip over it, but I really want to understand this stuff. Could > someone tell me how to get the *(compile-cmd osx) *call at the end of the > code to produce the expected output: *"/usr/bin/gcc" *? I have commented > out redundancy and moved a couple of lines for readability. Thanks in > advance! > > J > >> (ns joy.udp >> (:refer-clojure :exclude [get])) >> >> (defn beget [this proto] >> (assoc this ::prototype proto)) >> >> (defn get [m k] >> (when m >> (if-let [[_ v] (find m k)] >> v >> (recur (::prototype m) k)))) >> >> (def put assoc) >> >> ;;;;;;; compiler >> (defmulti compiler :os) >> (defmethod compiler ::unix [m] (get m :c-compiler)) >> (defmethod compiler ::osx [m] (get m :llvm-compiler)) >> >> (def clone (partial beget {})) >> > > >> (def unix {:os ::unix, :c-compiler "cc", :home "/home", :dev "/dev"}) >> > > >> (def osx (-> (clone unix) >> (put :os ::osx) >> (put :llvm-compiler "clang") >> (put :home "/Users"))) >> >> ;;;;;;; home >> (defmulti home :os) >> (defmethod home ::unix [m] (get m :home)) >> (defmethod home ::bsd [m] "/home") >> > > >> ;; the error on the call to (home osx) is contingent upon toggling the >> following lines. > > ;(derive ::osx ::unix) >> ;(derive ::osx ::bsd) >> (prefer-method home ::unix ::bsd) >> ;(remove-method home ::bsd) >> (derive (make-hierarchy) ::osx ::unix) >> >> ;;;;;;; compile-cmd >> (defmulti compile-cmd (juxt :os compiler)) >> >> (defmethod compile-cmd [::osx "gcc"] [m] >> (str "/usr/bin/" (get m :c-compiler))) >> >> (defmethod compile-cmd :default [m] >> (str "Unsure where to locate " (get m :c-compiler))) >> ;;;;;;;;;;;;;;;;;;;;;; >> >> (home osx) >> > ;=> java.lang.IllegalArgumentException: No method in multimethod 'home' >> for dispatch value: :joy.udp/osx … >> > ;; Should be: ;=> "/Users" > > > (compile-cmd osx) > > ;=> "Unsure where to locate cc" > > ;; Should be: ;=> "/usr/bin/gcc" > > > >> (compile-cmd unix) > > ;=> "Unsure where to locate cc" > > ;; this is the expected output > > -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.