Clojure from the Ground Up - Sequences - Exercises My answers to the exercises from: http://aphyr.com/posts/304-clojure-from-the-ground-up-sequences

gistfile1.clj

; Sequences
;--------------------------------------------------

; Write a function to find out if a string is a palindrome–that is, if it looks the same forwards and backwards.
(defn revStr
  "Reverses s and returns as a string"
  [s]
  (apply str (reverse s)))

(defn palindrome?
  [s]
  (= s (revStr s)))


; Find the number of ‘c’s in “abracadabra”.
(count (filter #(= % \c) "abracadabra"))
; Or
((frequencies "abracadabra") \c)

; Write your own version of filter.
(defn my-filter
  [pred coll]
  (reduce (fn [result val]
            (if (pred val)
              (conj result val) 
              result))
          []
          coll))


; Find the first 100 prime numbers
(defn divisible? [x y] (= (rem x y) 0))

(defn prime? [n]
  (not-any? #(divisible? n %) (range 2 n)))

(take 100 (filter prime? (iterate inc 2) ))

Thanks for this. As a beginner to the Clojure language, I did not know about the 'not-any?' function. That really makes the prime number problem easier.