Web Development with Clojure, 2nd Edition

Structuring the Code

One nontrivial difference between Clojure and imperative languages is the way the code is structured. In imperative style, it’s a common pattern to declare a shared mutable variable and modify it by passing it different functions. Each time we access the memory location, we see the result of the code that previously worked with it. For example, if we have a list of integers and we wish to square each one and then print the even ones, the following Python code would be perfectly valid:

l = range(1, 6)

for i, val in enumerate(l) :
  l[i] = val * val

for i in l :
  if i % 2 == 0 :
    print i

In Clojure this interaction has to be made explicit. Instead of creating a shared memory location and then having ...