Using your example--very helpful, BTW--I simplified it a bit more: user=> (def x 10) #'user/x user=> (def y #'x) #'user/y user=> y #'user/x user=> @y 10 user=> (def x (fn [me] (println "Welcome" me))) #'user/x user=> (y "hello") Welcome hello nil user=> (@y "yikes") Welcome yikes nil
What I come away with from this is a better understanding that when I refer to "y" in the above code, it's going to return a symbol. When I place this value in the first slot of a list, the symbol will act in its role as a function. Otherwise, if "y" is holding a reference to a symbol that is a value, like 10, then I need to dereference it to use it. user=> (def x 15) #'user/x user=> @y 15 user=> (y) java.lang.ClassCastException: java.lang.Integer cannot be cast to clojure.lang.IFn (NO_SOURCE_FILE:0) I believe that ClassCastException makes more sense to me now. Like you said, pointers. I suppose my brain just doesn't want to accept pointers in the JVM! On Feb 11, 3:59 am, Alan Malloy <a...@malloys.org> wrote: > In this case the var is simply acting as a mutable pointer, so that > when the implementation is changed the route reflects the new value. > Here's a simple example of that behavior in action, divorced from > webservers and the like: > > ;; caller accepts a function and returns a new one that forwards to it > repl-1=> (defn caller [f] (fn [x] (f x))) > ;; initially we use identity > repl-1=> (defn callee [x] x) > > ;; the first form passes the current value of callee; the second > passes the "pointer" > repl-1=> (def passed-value (caller callee)) > repl-1=> (def passed-var (caller #'callee)) > > ;; if we redefine callee, only the pointer-version sees the new value > repl-1=> (defn callee [x] (* 2 x)) > repl-1=> (passed-value 4) > 4 > repl-1=> (passed-var 4) > 8 > > On Feb 11, 2:11 am, Sean Bowman <pico...@gmail.com> wrote: > > > > > > > > > I've been working with Compojure and Ring lately to build an app > > server, and I've gotten my brain stuck trying to figure out wrap- > > reload. It seems like I have to turn my routes into vars to get wrap- > > reload to work, but I don't understand why, and I suppose I don't > > really understand the "when" or "where" of the situation either. > > > For example, if I have a bunch of resource namespaces with > > (defroutes ...) calls in them, and a main "core" namespace that > > aggregates them all, wrap-reload will work in a scenario like this: > > > (defroutes combined > > #'myapp.resource.users > > #'myapp.resource.products > > #'myapp.resource.other > > (route/resources "/") > > (route/not-found "Page not found")) > > > In the above, changing code in any of the resource namespaces auto- > > reloads them. > > > But if I put two defroutes in the same namespace and try to "var" one > > of them, wrap-reload fails: > > > (defroutes defaults > > (route/resources "/") > > (route/not-found "Page not found")) > > > (defroutes all-routes > > myapp.resource.users > > myapp.resource.products > > myapp.resource.other) > > > (defroutes combined > > #'all-routes > > defaults) > > > If I pass combined to (handler/site ...) in Compojure, wrap-reload > > doesn't work. > > > And, if I take the original, and remove the vars, then try to call > > handler/site and var that route, it doesn't work either: > > > (defroutes combined > > myapp.resource.users > > myapp.resource.products > > myapp.resource.other > > (route/resources "/") > > (route/not-found "Page not found")) > > > (def app (handler/site #'combined)) > > > What am I not understanding here? I feel like this is the area I > > struggle with most, and I'm not getting it at all. > > > P.S. Please don't point me at lein-ring and have me just run that. > > I'm trying to finally understand this, and I also need to be able to > > access the REPL in the same classloader as the running server for > > other reasons. -- 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
