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this is my first question here and i hope you can help me. I am programming a merge function in clojure. I test my code on tryclojure and got the error in the title.

Here is my Code

(def merge
(fn [lon1 lon2]
{:pre[(every? number? lon1)(every? number? lon2)]
:post[(every? number? %)]}
(cond
(empty? lon1) lon2
(empty? lon2)lon1
:else
(cons (min (first lon1) (first lon2))
(merge (rest lon1) (rest lon2))))))
#'sandbox7750/merge
> (merge (1,2,5) (3,4))
java.lang.ClassCastException: java.lang.Long cannot be cast to clojure.lang.IFn

So, whats the Problem here? Looking forwards to an answer :)

greetings

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  • Could you please enhance your question? (code indents, upper/lower case letters in sentences) Commented Jun 6, 2016 at 9:53

2 Answers 2

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First of all you need to quote lists otherwise they are evaluated and their first element is treated as a function to be called and thus the exception:

(1,2,5)
;; => java.lang.ClassCastException: java.lang.Long cannot be cast to clojure.lang.IFn

Quoting will help you to get a list with numbers:

'(1,2,5)
;; => (1 2 5)

It's also more idiomatic to not use element separator (like ,) and you can see the form printed above ((1 2 5)).

As it seems it's an exercise, I will let you fix other issues in your merge function.

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  • Thanks for your Input, it was an excercise indeed. I also had some minor mistakes in my else part. Here is the new and working code: code (def merge (fn [lon1 lon2] {:pre[(every? number? lon1)(every? number? lon2)] :post[(every? number? %)]} (cond (empty? lon1) lon2 (< (first lon1) (first lon2)) (cons (first lon1) (merge (rest lon1) lon2)) :else (cons (first lon2) (merge lon1 (rest lon2)))))) Commented Jun 9, 2016 at 7:26
  • isnt there something like auto formatting? this code sucks to read.. Commented Jun 9, 2016 at 7:28
  • You can just copy formatted code from your editor, paste it into StackOverflow editor, select the code snippet and click the {} icon to mark it as code snippet. Commented Jun 9, 2016 at 7:31
  • well this wont work in the add comment section :) as you can see my first post was formated. Thanks for your help, i am good now Commented Jun 9, 2016 at 7:51
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The right call is (merge '(1 2 3) '(4 5)) or (merge [1 2 3] [4 5]) (commas is optional). When you write unquoted list (1,2,3) a first element considered as the function. 1 is not a function and you get the error message.

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