*Note that these are not good examples of idiomatic Clojure coding style, but more of an introduction to functional programming using Clojure.*

Here is the basic definition for the function of a square, which takes x as a variable:

(defn square [x] (* x x))

call the function like this and this is the result you get

=> (square 4)

16

(defn addone [a] (inc a))here are a couple renditions I went through of refactoring the sum of squares function and making it more generic this is not idiomatic clojure code, but the easiest to understand

(defn sumsquare [a b] (if (> a b) 0 (+ (* a a) (sumsquare (+ a 1) b))))

now we take the squaring (* a a) out of the code and replace it with a function that can be passed in

(defn sum [fn a b] (if (> a b) 0 (+ (fn a) (sum fn (+ a 1) b))))

and here we replace the explicit increment (+ a 1) with a passed in function

(defn sum2 [func incr a b] (if (> a b) 0 (+ (func a) (sum2 func incr (incr a) b))))

with help from the Google Clojure newsgroup here is a more idiomatic example

(defn sum3 [func incr a b] (if (> a b) 0 (reduce + (map func (take-while #(<= % b) (iterate incr a))))))

and yet another even more idiomatic example, using an anonymous function and the invocation of its arguments (see the let post for more on this)

(defn sum4 [func incr a b] (loop [accum 0 x a] (if (> x b) accum (recur (+ (func x) accum) (incr x)))))