small update: I found that the problem happens because make-adder returns a closure; with a simple function it works:
(defn make-2-adder [] (fn [x] (+ 2 x))) (def g2 (make-2-adder)) (eval `(let [~'f ~g2] (~'f 5))) ; --> 7 On Thursday, January 14, 2016 at 12:52:47 PM UTC+1, gianluca torta wrote: > > Hi Burt, > > I have done some investigation, further reducing your issue to the > following: > > (def g (make-adder 2)) > (eval `(let [~'f ~g] (~'f 5))) > ; --> error IllegalArgumentException No matching ctor found for class > user$make_adder$fn__7609 etc. > > (defn h [x] (+ x 2)) > (eval `(let [~'f ~h] (~'f 5))) > ; --> 7 > > but it is still not completely clear to me why they behave differently > > hth, > Gianluca > > > > On Thursday, January 14, 2016 at 11:05:55 AM UTC+1, 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.
