CODEWITHSUNDEEP
clojurelisp
boucekv
boucekv

Reputation: 1230

How to make list by recursion?

In many cases I want to make list by recursion function an I can not find right way how to do it.

For example (Not usefull but shortest I can find) I want to take elements from list one by one and create new list that is same as first one.

(defn f [x] (list 
          (first x) 
          (if (not= (rest x) '())
          (f (rest x))
          '()       
)))

(f '(1 2 3))

I want to get

(1 2 3)

but I get

(1 (2 (3 ())))

I want to do not use flatten. For example this imput

(f '([1 1] [2 2] [3 3]))

will be destroyed by flatten.

Upvotes: 2

Views: 159

Answers (1)

Mikhail Vladimirov
Mikhail Vladimirov

Reputation: 13890

Replace list with cons:

(defn f [x] 
  (cons (first x) 
        (if (not= (rest x) '())
          (f (rest x))
          '())))

Operation (list x y) returns list of two elements: (x y). Operation (cons x y) returns list which head (i.e. first element) is x and tail (the rest of the list) is y where y should be list itself.

Upvotes: 4

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