Pure Functions Powers

Clojure provides functions that can derive new functions from old functions.

comp

Composing pure functions is a common task in FP so Clojure provides comp to compose any number of functions to create a new function.

1((comp inc *) 2 3)
2; => 7

Code written with comp is more elegant because it conveys more meaning.

memoize

Memoization takes advantage of referential transparency by storing the arguments passed to a function and the return value of the function. With this subsequent calls to the function with the same arguments can return the result immediately.

 1(defn timed-identity
 2  [x]
 3  (Thread/sleep 1000)
 4  x)
 5
 6(timed-identity "hello")
 7; => "hello" after 1 second
 8
 9(def memo-timed-identity (memoize timed-identity))
10(memo-timed-identity "hello")
11; => "hello" after 1 second
12
13(memo-timed-identity "hello")
14; => "hello" immediately