Re: Question concerning eval
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.
Re: Question concerning eval
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.
Question concerning eval
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.
Re: Question concerning eval
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.
Re: Question concerning eval
Hi Adrian, Gianluca, I understand that quoting the entire binding vector avec solves my problem. @Adrian Thanks for the hint. But nethertheless, it's a riddle for me why there's a difference between my original approaches. cheers, Burt -- 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.
Re: Question concerning eval
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.
