define-values macros in Clojure

Question

Is it possible to write a define-values macros in Clojure? Racket language provides such a thing like define-values form which acts in this way

(define -values '(a b c) (1 2 3))

Where a, b, c are global variables now. How can I do it in Clojure?


(defmacro defvar [x y]                                                     
     `(let [a# ~x                                                              
            b# ~y]                                                             
        (def b# a#)))                                                          
                                                                               
                                                                               
  (println (defvar 'a 2))


=> #'user/b__2__auto__

;;;It binds the value to  auto generated symbol

amalloy · Accepted Answer · 2023-02-03 15:57:45Z

4

define-values doesn't make any sense in Clojure. It makes sense in Racket because values lets one expression evaluate to multiple values. In Clojure, an expression always evaluates to exactly one value: there's no values to extract into definitions.

Of course, you can write a macro def-several-things such that

(def-several-things [x y] [1 2])

expands to

(do (def x 1)
    (def y 2))

but this is less readable, not more, so nobody does it.

answered Feb 3, 2023 at 15:57

amalloy

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4 Comments

user324885 Over a year ago

I just want to know how to do that

user2609980 Over a year ago

@user324885 i.imgur.com/ccTqs7N.png

(defmacro def-several-things [symbols values]   `(do ~@(map (fn [s v] (list 'def s v)) symbols values)))  (macroexpand  '(def-several-things [x y] [1 2]))

amalloy Over a year ago

@user2609980 If you have an answer to the question, please post it as an Answer, not as a comment on my answer.

user2609980 Over a year ago

@amalloy this is an answer to the comment. @user324885 asked how to write out your suggestion of using a macro def-several-things.

user2609980 · Accepted Answer · 2023-06-29 08:53:36Z

1

Note you can also use clojure.template/do-template:

(clojure.template/do-template
  [name val]
  (def name val) a 1 b 2 c 3)

this will give you vars a b c with vals 1 2 3.

Expansion:

(clojure.walk/macroexpand-all '(do-template [name v] (def name v) a 1 b 2 c 3))
;; => (do (def a 1) (def b 2) (def c 3))

answered Jun 29, 2023 at 8:53

user2609980

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