Compact way in Clojure to print a variable number of command line arguments?

Question

I'm a newbie to Clojure. I think I'm trying to solve this procedurally and there must be a better (more functional) way to do this in Clojure...

The -main function can receive a variable number of 'args'. I would like to print them out but avoid an IndexOutOfBoundsException. I thought I could mimic Java and use a case fall-through to minimize the code involved, but that didn't work:

(defn -main [& args]
  (println "There are" (str (count args)) "input arguments.")
  (println "Here are args:" (str args))
  (let [x (count args)]
    (case x
      (> x 0) (do
          (print "Here is the first arg: ")
          (println (nth args 0)))
      (> x 1) (do
          (print "Here is the 2nd arg: ")
          (println (nth args 1)))
      (> x 2) (do
          (print "Here is the 3rd arg: ")
          (println (nth args 2))))))

Gwang-Jin Kim · Accepted Answer · 2020-08-09 10:52:31Z

3

(doseq [[n arg] (map-indexed vector arguments)]
  (println (str "Here is the argument #" (inc n) ": " (pr-str arg))))

map-indexes is like map but adds index number in the beginning. So it goes item by item through arguments, packs index and item into a vector and by destructruing index number and item are mapped to [n arg].

Since clojure begins counting from 0, you use (inc n) to begin counting from 1. pr-str is pretty print string. The str joins all string components together.

edited Aug 9, 2020 at 10:52

Gwang-Jin Kim

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answered Aug 9, 2020 at 5:50

akond

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leetwinski · Accepted Answer · 2020-08-10 07:10:09Z

0

there is also a handy formatting facility in clojure's core library: cl-format, which is the port of common lisp's format syntax. It includes a nice way to print out collections:

(require '[clojure.pprint :refer [cl-format]])

(let [args [:a :b :c :d]]
  (cl-format true "~{here is the ~:r arg: ~a~%~}"
             (interleave (rest (range)) args)))

;; here is the first arg: :a
;; here is the second arg: :b
;; here is the third arg: :c
;; here is the fourth arg: :d

some more information about what format can do is here

answered Aug 10, 2020 at 7:10

leetwinski

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2 Comments

Corba the Geek Over a year ago

Can the cl-format library handle a variadic function with a variable number of parameters instead of a set vector?

leetwinski Over a year ago

sure, there is no difference

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