Building a string in Clojure with recursion

Question

I need to generate a random char and build a string and only stop when my string contains the newly generated char.


(defn rand-char [len]
  (apply str (take len (repeatedly #(char (+ (rand 26) 65))))))

(def random-string
  (loop [x (rand-char 1)
         result []]
    (if (some #(= x %) result)
      (apply str (conj result x))
      (recur (conj result x) (x (rand-char 1))))))

I am getting

java.lang.String cannot be cast to clojure.lang.IFn

Lee · Accepted Answer · 2019-08-15 09:02:13Z

2

rand-char returns a string but in (x (rand-char 1)) you're attempting to call x as a function, hence the error. You only need to call rand-char to generate the next random string to try. The arguments to recur should be in the same order as those declared in the loop so yours are in the wrong order:

(recur (rand-char 1) (conj result x))

answered Aug 15, 2019 at 9:02

Lee

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3 Comments

Lee Over a year ago

@rake-write-code - Do you want random-string to be a function? At the moment you're using def so it's being evaluated to a vector. (random-string) is trying to call the vector as a function. Vectors are functions from an index to the corresponding value e.g. ([1 2 3] 0) => 1 so you get the error because you haven't supplied enough arguments. It looks like you should defined random-string using defn e.g. (defn random-string [] ...).

rake-write-code Over a year ago

Hi @lee, Thanks for all the pointers, it is supposed to be a method and I've been able to run it by just passing 0 as a parameter. I have been able to print a correct string but I want it returned instead and it evaluates to a null reference.

(def random-string   (loop [x (rand-char 1)          result ""]     (if (.contains result x)       (println (str result x))       (recur (rand-char 1) (str result x)))))

but I don't want to print it but instead return it. just returning (str result x) says java.lang.String cannot be cast to clojure.lang.IFn .

rake-write-code Over a year ago

Thanks for your help @lee, I got it. I just needed to pass a vector to the function when I define it.

papachan · Accepted Answer · 2019-08-15 12:25:21Z

1

something like this does it serve you?

(defn random-string []
  (loop [x (rand-char 1)
         result []]
    (if (.contains result x)
      (apply str result)
      (recur (rand-char 1) (conj result x)))))

answered Aug 15, 2019 at 12:25

papachan

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1 Comment

rake-write-code Over a year ago

Thanks for your help. I have already accepted Lee's answer, I have since also opted to build result directly as a string.

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