CODEWITHSUNDEEP
clojurenested-loops
Hakan Özler
Hakan Özler

Reputation: 988

using a nested function in clojure

I am trying to make a nested function that should be run recursively in Clojure in order to collect some information. I have seen some techniques such as fn, loop, doseq but I am not good with them for now.

First let me explain why I want to use a recursive funtion: I have a class and this class include 2 methods itself, these methods are namely getLeft() and getRight(), plus the return type of the methods are also a class. I do want simply traverse all getLeft and getRight methods in order to get the proper number from them.

Just to be clear, I put a schema:

My Main Class:

                     +-- getRight(): class  - getLeft/getRight
++ getLeft(): class ---  
                     +-- getLeft((): class  - getLeft/getRight
                     +-- getRight(): class  - getLeft/getRight
++ getRight() :class
                     +-- getLeft((): class  - getLeft/getRight

I also made a function called "loopingP" but when I add this func to my another function, it gives an error. Error: NullPointerException org.mtrcclojure.demo/loopingP (NO_SOURCE_FILE:4)

     (defn loopingP [points]
       (if (= (getKind points) 5)
        ( (loopingP (getRight points)) (loopingP (getLeft points)))
       (if (= (getKind points) 3) (println "Yep"))))

How can I properly use a nested function in Clojure for my purpose? Thanks in advance!

Solution is: putting a [] 

(defn loopingP [points]
       (if (= (getKind points) 5)
        [ (loopingP (getRight points)) (loopingP (getLeft points))]
       (if (= (getKind points) 3) (println "Yep"))))

Upvotes: 0

Views: 1083

Answers (1)

noisesmith
noisesmith

Reputation: 20194

You have an extraneous set of parenthesis around your recursion case - perhaps you meant to group the getRight and getLeft calls into a pair? the base case always returns nil (either from the false branch of the if, or from the println) so the leftmost recursion gets applied, and thus you call nil as a function (leading to a NullPointerException).

Upvotes: 1

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