CODEWITHSUNDEEP
clojure
Tiago Alves
Tiago Alves

Reputation: 2316

Understanding the return of a recursive function

I am new to Clojure and am trying to understand why the two functions below are different.

First

(defn rp [i]
  ((println i)
   (if (> i 3)
     (println "bye")
     (rp (inc i)))))

Second

(defn rp
  ([i] (println i)
       (if (> i 3)
         (println "bye")
         (rp (inc i)))))

When I call them with (rp 0), the first prints

0
1
2
3
4
bye
CompilerException java.lang.NullPointerException, compiling:(/Users/...)

and the second prints

0
1
2
3
4
bye
=> nil

Why are they different? Why the first function triggers a NullPointerException?

Upvotes: 0

Views: 74

Answers (1)

cfrick
cfrick

Reputation: 37073

Your first example has parens around the body and calls the result of (println i) (which is nil) as a function. E.g. ((println :a) :b) throws. Most likely related to your experiments with the different arities in your second example.

Upvotes: 2

Related Questions