Python's range() analog in Common Lisp


Question

How to create a list of consecutive numbers in Common Lisp?

In other words, what is the equivalent of Python's range function in Common Lisp?

In Python range(2, 10, 2) returns [2, 4, 6, 8], with first and last arguments being optional. I couldn't find the idiomatic way to create a sequence of numbers, though Emacs Lisp has number-sequence.

Range could be emulated using loop macro, but i want to know the accepted way to generate a sequence of numbers with start and end points and step.

Related: Analog of Python's range in Scheme

1
29
5/23/2017 12:13:54 PM

Accepted Answer

There is no built-in way of generating a sequence of numbers, the canonical way of doing so is to do one of:

  • Use loop
  • Write a utility function that uses loop

An example implementation would be (this only accepts counting "from low" to "high"):

(defun range (max &key (min 0) (step 1))
   (loop for n from min below max by step
      collect n))

This allows you to specify an (optional) minimum value and an (optional) step value.

To generate odd numbers: (range 10 :min 1 :step 2)

35
11/8/2013 11:17:42 PM

alexandria implements scheme's iota:

(ql:quickload :alexandria)
(alexandria:iota 4 :start 2 :step 2)
;; (2 4 6 8)

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