Programming Clojure, 3rd Edition

Where’s My for Loop?

Clojure has no for loop and no direct mutable variables. Clojure provides indirect mutable references, but these must be explicitly called out in your code. See Chapter 6, ​State and Concurrency​ for details. So how do you write all that code you’re accustomed to writing with for loops?

Rather than create a hypothetical example, we decided to grab a piece of open source Java code (sort of) randomly, find a method with some for loops and variables, and port it to Clojure. We opened the Apache Commons project, which is very widely used. We selected the StringUtils class in Commons Lang, assuming that such a class would require little domain knowledge to understand. We then browsed for a method that had multiple for loops and ...