Problem 4 : java.lang.Long cannot be cast to clojure.lang.IFn

[Roelof Wobben]

Problem 4 looks like this :

(= __ (conj '(2 3 4) 1))

So in my opinion the answer must be (1 2 3 4)

But then I see this error :  java.lang.ClassCastException: java.lang.Long cannot be cast to clojure.lang.IFn

Can anyone give me a hint what I do wrong ?

Roelof

[Robert Marianski]

(1 2 3 4) tries to call 1 as a function.

Try quoting it: '(1 2 3 4)

Or: (list 1 2 3 4)

Robert

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[Seven Hong]

If you write (1 2 3 4) there, then Clojure REPL will think 1 is a function as 1 is placed at first place of the list. In Clojure, integer number is Long type by default, and since REPL is considering 1 as a function, it's trying to convert 1's type(which is Long) into function type(which is IFn) by casting it. That's why you have this error message.

You were right, conj-ing a 1 into list of 2 3 4, is a list of 1 2 3 4. You just need a quote in front of the list in order to stop REPL evaluating the list as a function call. That's why it's '(1 2 3 4).