Nathan, Just to confirm two things in eval-expr:
1. Should seq be seq? 2. It looks like you still need to a. have a global x defined to evaluate eval-expr and b. need to wrap the call to eval-expr with binding in order to get a non-global binding for x (let doesn't seem to do the trick). -Greg On Jan 17, 2:15 pm, Nathan Kitchen <nathan.kitc...@gmail.com> wrote: > On Sat, Jan 17, 2009 at 11:06 AM, Greg Harman <ghar...@gmail.com> wrote: > > > Meta: This thread is a revival and continuation of last month's > > discussion at: > >http://groups.google.com/group/clojure/browse_thread/thread/e1226810b... > > > --- > > > Nathan, did you ever come up with a better way to do this than using a > > global var? > > > One solution is to use (binding), which still requires a global var, > > but gives each eval it's own binding of that var: > > > user=> (def x) > > #'user/x > > user=> (def expr '(+ x 4)) > > #'user/expr > > user=> (binding [x 3] (eval expr)) > > 7 > > user=> x > > java.lang.IllegalStateException: Var user/x is unbound. > > (NO_SOURCE_FILE:0) > > I tried this approach with (binding) and I also tried creating > anonymous functions from the expressions: > > (eval (list 'fn '[x] expr)) > > Creating functions didn't work for me because I used up the PermGen > space in the garbage collector with all the > classes created to implement them. As best I remember, I got the same > outcome with (binding), even though I wasn't creating new functions. > > The approach that worked for me was to create my own recursive > evaluation function: > > (defn eval-expr [expr] > (cond > (seq expr) > (let [[op & args] expr] > (apply @(resolve op) (map eval-expr args))) > (= expr 'x) x > :else expr)) > > I'm still using the var x, but it's not inherent to the approach; you > could easily add a map of symbols to values as an additional argument. > > -- Nathan --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
