Mutation alters a value or variable’s state after it has been established. Imperative iteration commonly depends on mutation: a loop updates a counter so its termination test eventually succeeds. Clojure instead steers this changing state through recursion, sequence construction, and controlled side effects. section 3.4.4 section 20.5
Mutation appears here mainly as a contrast between imperative state changes and functional iteration:
- Java’s do-while example increments a mutable count inside the loop body. section 3.4.4
- Clojure passes the changing count as a recur argument, using loop-recur and a condition to control termination. section 3.4.4
- List comprehensions assemble a sequence of values instead of repeatedly mutating the value checked by the loop. section 3.4.4
- Clojure permits necessary side effects but regulates them and encourages applications toward functional purity. section 20.5
Replacing a mutable counter
An imperative loop prints counts 1 through 3 by incrementing count. The Clojure version carries that state explicitly: (loop [count 1] (when (< count 4) (println "Count is:" count) (recur (inc count)))). A second version accumulates [1 2 3] with conj, while map, for, and dorun provide sequence-oriented alternatives. section 3.4.4
(loop [count 1]
(when (< count 4)
(println "Count is:" count)
(recur (inc count))))
;; Count is: 1
;; Count is: 2
;; Count is: 3
;; nil
Inspect the direct Clojure translation of a mutable Java counter loop, including explicit state progression and termination. section 3.4.4
