Programming Clojure, 3rd Edition

Lazy and Infinite Sequences

Most Clojure sequences are lazy; in other words, elements are not calculated until they’re needed. Using lazy sequences has many benefits:

• You can postpone expensive computations that may not in fact be needed.
• You can work with huge data sets that don’t fit into memory.
• You can delay I/O until it’s absolutely needed.

Consider the code and following expression that produces (mostly) prime numbers using wheel factorization:^[19]

src/examples/primes.clj

(ns examples.primes)
;; Taken from clojure.contrib.lazy-seqs
; primes cannot be written efficiently as a function, because
; it needs to look back on the whole sequence. contrast with
; fibs and powers-of-2 which only need a fixed buffer of 1 or 2
; previous ...