range - Clojure Standard Library

For a quick intro to this series of blog posts check out Clojure Standard Library - Intro. It includes a lot of useful info, including notes about presentation of examples and more.

This posts function:

range

Quick Overview

Description

clojure.core/range is a function that returns a lazy sequence of numbers. The sequence is constructed using the parameters provided.

Example

(range 10)
; => (0 1 2 3 4 5 6 7 8 9)

Here I have passed range the integer 10, and range returned a list of numbers 0 through 10.

How To Use

Parameters and Return Values

range has three parameters that all have default values. Each parameter accepts a number, which can be an integer or a float and can also be negative.

Parameter Structure

range is a multiple arity function – it accepts a variable number of parameters, up to three. It behaves differently based on the number of parameters (arity overloading).

• (range) When given zero parameters, range returns an infinite lazy sequence of every integer from 0 to infinity. The reason is that (as seen above) the default values for start, end and step are 0, infinity and 1.

  Ex: ¹

(take 10 (range))
; => (0 1 2 3 4 5 6 7 8 9)
(take 20 (range))
; => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19)
(take 30 (range))
; => (0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29)

• (range end) If only one number is given then it will be used as the end value. (start=0, step=1)

  Ex:

(range 10)
; => (0 1 2 3 4 5 6 7 8 9)
(range 10.001)
; => (0 1 2 3 4 5 6 7 8 9 10)

• (range start end) If two numbers are given then the first one will be used for start and the second for end. (step=1) If start is equal to end, range will return an empty list.

  Ex:

(range 0 10)
; => (0 1 2 3 4 5 6 7 8 9)
(range 200 200)
; => ()
(range 0.5 10.5)
; => (0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5)
(range 0 -10)
; => ()
(range -15 -10)
; => (-15 -14 -13 -12 -11)
(range -15 0)
; => (-15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1)
(range -15.5 0)
; => (-15.5 -14.5 -13.5 -12.5 -11.5 -10.5 -9.5 -8.5 -7.5 -6.5 -5.5 -4.5 -3.5 -2.5 -1.5 -0.5)

• (range start end step) When given three numbers, the first one is used for start, second for end and the third for step.

  Ex:

(range 0 10 1)
; => (0 1 2 3 4 5 6 7 8 9)
(range 0 10 0.5)
; => (0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5)
(range 0 -10 -1)
; => (0 -1 -2 -3 -4 -5 -6 -7 -8 -9)