Decimal to Binary Clojure - clojure

Question

I'm following this pseudo code to convert decimal to binary recursively.
findBinary(decimal)
if (decimal == 0)
binary = 0
else
binary = decimal % 2 + 10 * (findBinary(decimal / 2)
This is what I have tried:
(defn binary [n]
(loop [res 0]
(if (= n 0)
res
(recur (res (* (+ (mod n 2) 10) (binary (quot n 2)))) )
)
)
)
But I get this error :
ClassCastException java.lang.Long cannot be cast to clojure.lang.IFn user/binary (form-init9002795692676588773.clj:6)
Any ideas how to fix the code to complete the task?

Answer 1

I realize, that this is about the journey and not the result. But to
have it mentioned: Long/toString can give you a string from a number with a wide
variety of radixes.
(Long/toString 123 2)
; → "1111011"

Answer 2

Here's a slightly different approach which allows recur to be used:
(defn find-binary [d]
(loop [ decimal d
digits '() ]
(if (= decimal 0)
(Integer. (clojure.string/join (map str digits)))
(recur (quot decimal 2) (conj digits (mod decimal 2))))))
In the loop we build up a collection of binary digits, adding each new digit at the beginning of the list so that we end up with the digits in the desired order left-to-right in the list. When the terminating condition is reached we convert the collection-of-digits to a collection-of-strings, join the collection of strings together into single string, and convert the string back to an integer.

Answer 3

Your psuedo code can be expressed pretty directly in clojure:
(defn find-binary [decimal]
(if (= decimal 0)
0
(+ (mod decimal 2) (* 10 (find-binary (quot decimal 2))))))
Examples:
user=> (find-binary 1)
1
user=> (find-binary 2)
10
user=> (find-binary 25)
11001
user=> (find-binary 255)
11111111
The error in your version is here:
(recur (res (* (+ (mod n 2) 10) (binary (quot n 2))))
Specifically, the complaint is that you are trying to use res (which has the value 0) as a function.
To be honest, I'm not sure how to do this with loop-recur. When I try it complains about recur not being from the tail position. Perhaps another answer can enlighten us!

Answer 4

Using recur:
;; returns a binary number string of the given decimal number
(defn find-binary [decimal]
(loop [n decimal
res ""]
(if (= n 0)
res
(recur (quot n 2)
(str (mod n 2) res)))))
But without loop:
(defn find-binary [decimal & {:keys [acc] :or {acc ""}}]
(if (= decimal 0)
acc
(find-binary (quot decimal 2) :acc (str (mod decimal 2) acc))))
The original attempt was the following, but it can't go far in the size of decimal:
(defn find-binary [decimal]
(loop [n decimal ;; number to be binarized
res '() ;; collector list
pos 0] ;; position of binary number
(if (= n 0)
(reduce #'+ res) ;; sum up collector list
(recur (quot n 2)
(cons (* (int (Math/pow 10 pos))
(mod n 2))
res)
(+ 1 pos)))))
For large numbers use: