在clojure代码中期望有什么功能？

Question

going through the exercises in the fp-oo book and i'm having trouble with an early exercise to add squares. Here's my code:

 (defn square [n]
   (* n n))

 (defn add-squares [l]
   (cond
     (nil? l) 0
     :else (+ (square (first (l))) (add-squares (rest (l))))))

This example:

(add-squares '(2 2 2 2))

should return

16

but fails with this exception:

ClassCastException clojure.lang.PersistentList cannot be cast to clojure.lang.IFn  user/add-squares (NO_SOURCE_FILE:4)

which i guess means i'm trying to pass a function somewhere instead of a list which was expected. Can someone tell me which part of the code is the culprit?

Thanks, James

Answer 1

This is wrong:

(first (l))

This means that you are calling l as a function.

You should use:

(first l)

And of course, the same thing for (rest (l))