Hi Adrian, with your suggestion it certainly works also with avec'
however, I still don't see why the original code from Burt works with avec and does not work with avec' cheers, Gianluca On Thursday, January 14, 2016 at 5:06:02 PM UTC+1, adrian...@mail.yu.edu wrote: > > You need to quote the entire vector `avec`, because otherwise the function > you want to bind to `foo` will be evaluated before being evaluated by the > `let` special operator, which expects only standard readable object > literals to be embedded. > > Try changing: > > (def avec > ['p true > 'foo (fn [x] (+ 2 x))]) > > > to: > > > (def avec > '[p true > foo (fn [x] (+ 2 x))]) > > > On Thursday, January 14, 2016 at 5:05:55 AM UTC-5, Burt wrote: >> >> Hi, >> >> I got an exception using eval and I do not understand why! >> Can anybody explain what happens? >> >> Here is a small piece of code showing the problem: >> >> (defn eval-phi [avec phi] >> (eval `(let ~avec ~phi))) >> >> ; The idea of eval-phi is the evaluation of >> ; arbitrary lists where the symbols are >> ; defined in avec >> >> ; example: >> ; in avec the symbol p is defined as true >> ; and the symbol foo as a function adding 2 >> >> (def avec >> ['p true >> 'foo (fn [x] (+ 2 x))]) >> >> ; here are two lists >> (def phi '(and p (= 7 (foo 5)))) >> (def psi '(and (not p) (= 7 (foo 5)))) >> >> ; and here their evaluation >> (eval-phi avec phi) >> ; => true >> (eval-phi avec psi) >> ; => false >> >> ; second approach: >> ; the attempt to give the definition of a >> ; function in avec by a function which >> ; returns a function leads to an exception: >> >> (defn make-adder [n] >> (fn [x] (+ n x))) >> >> ((make-adder 2) 5) >> ; => 7 >> >> ; here the second definition of a binding vector: >> (def avec' >> ['p true >> 'foo (make-adder 2)]) >> >> (eval-phi avec' phi) >> ; CompilerException java.lang.ExceptionInInitializerError >> >> ; in my mental model of the substitution of symbols by >> ; their value there should be no difference between the >> ; first approach and the second. >> >> ; Actually avec' contains the function returned by make-adder >> ((nth avec' 3) 5) >> ; => 7 >> >> ; Why does avec' leads to an exception? >> >> >> *Kind regards,* >> >> *Burkhardt Renz* >> >> -- 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.
