Iota is a very simple Emacs package that allows you to easily perform enumerations. It makes use of the iota-regexp variable to match substrings within a region. These substrings are then replaced with incrementing integers, although more complex enumeration is also possible.

Iota is available through MELPA:

(use-package iota)

It’s recommended however that you bind the Iota functions to keybindings for easy access:

(use-package iota
  :bind (("C-c i" . #'iota)
         ("C-c I" . #'iota-complex)))

One important part of Iota is the iota-regexp variable. By default iota-regexp is set to "\\<N\\>", so to create an ordered-list you could execute iota on the following region:

Before calling ‘iota’:

  N. List item
  N. Another list item
  N. Final list item

After calling ‘iota’:

  1. List item
  2. Another list item
  3. Final list item

By default the iota function replaces all matches with an incrementing number beginning with 1, however you can begin at any point by specifying the universal argument. For example, to begin the list above at 4, you could run C-u 4 M-x iota RET.

If for whatever reason however you want something that isn’t increments by 1, then you can make use of the iota-complex function. iota-complex works mostly the same as iota except you get prompted for two values. The first value is the initial value to start at. The second and perhaps more interesting value is the function to use to generate the next numerical value. You can provide any valid emacs-lisp expression so long as it evaluates to a function that takes one numerical parameter and returns an integer:

Before calling ‘iota-complex’:

  #define BIT1 N
  #define BIT2 N
  #define BIT3 N
  #define BIT4 N
  #define BIT5 N
  #define BIT6 N
  #define BIT7 N
  #define BIT8 N

After calling ‘iota-complex’ with ‘initial’ as 1 and ‘function’ as
‘(lambda (x) (* 2 x))’:
  
  #define BIT1 1
  #define BIT2 2
  #define BIT3 4
  #define BIT4 8
  #define BIT5 16
  #define BIT6 32
  #define BIT7 64
  #define BIT8 128

Or perhaps if you want to enumerate in the negative direction:

Before calling ‘iota-complex’:

  It started at N and then dropped to N!

After calling ‘iota-complex’ with ‘initial’ as ‘-3’ and ‘function’ as ‘1-’:

  It started at -3 and then dropped to -4!