pythoncommon-lispnumber-sequence

Python's range() analog in Common Lisp


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


Solution

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

    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)