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
