using a nested function in clojure

Question

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"))))

What is points in your example?

guilespi
– guilespi

2013-11-20 17:39:45 +00:00
Commented Nov 20, 2013 at 17:39 — guilespi
– guilespi, Commented Nov 20, 2013 at 17:39
points means a poincut class that is included in ajdt

Hakan Özler
– Hakan Özler

2013-11-20 17:42:41 +00:00
Commented Nov 20, 2013 at 17:42 — Hakan Özler
– Hakan Özler, Commented Nov 20, 2013 at 17:42

noisesmith · Accepted Answer · 2013-11-20 17:45:50Z

1

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).

answered Nov 20, 2013 at 17:45

noisesmith

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5 Comments

Hakan Özler Over a year ago

if I eliminate one nested call from the loopingP , the function receives me a string "Yep". But How can I use two nested call for left and right?

juan.facorro Over a year ago

If you were trying to build a tuple with two elements, you can use the vector literal [(loopingP (getRight points)) (loopingP (getLeft points))].

Hakan Özler Over a year ago

yes exactly I did like your answer @juan.facorro and I have received now this output : [[5 _0] nil] nil]. how can I split them?

juan.facorro Over a year ago

I don't exactly know what you mean by splitting them. What is the final result you hope to get?

juan.facorro Over a year ago

Onw way to do it is flattening the result and then filtering non nil elements: (->> points loopingP flatten (filter identity)).

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