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|
;;; random.el --- Functions for working with randomness -*- lexical-binding: t -*-
;; Author: William Carroll <wpcarro@gmail.com>
;;; Commentary:
;; Functions for working with randomness. Some of this code is not as
;; functional as I'd like from.
;;; Code:
(require 'prelude)
(require 'number)
(require 'math)
(require 'series)
(require 'list)
(require 'set)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Library
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defun random/int (x)
"Return a random integer from 0 to `X'."
(random x))
;; TODO: Make this work with sequences instead of lists.
(defun random/choice (xs)
"Return a random element of `XS'."
(let ((ct (list/length xs)))
(list/get
(random/int ct)
xs)))
(defun random/boolean? ()
"Randonly return t or nil."
(random/choice (list t nil)))
;; TODO: This may not work if any of these generate numbers like 0, 1, etc.
(defun random/uuid ()
"Return a generated UUID string."
(let ((eight (number/dec (math/triangle-of-power :base 16 :power 8)))
(four (number/dec (math/triangle-of-power :base 16 :power 4)))
(twelve (number/dec (math/triangle-of-power :base 16 :power 12))))
(format "%x-%x-%x-%x-%x"
(random/int eight)
(random/int four)
(random/int four)
(random/int four)
(random/int twelve))))
(defun random/token (length)
"Return a randomly generated hexadecimal string of LENGTH."
(->> (series/range 0 (number/dec length))
(list/map (lambda (_) (format "%x" (random/int 15))))
(list/join "")))
;; TODO: Support random/sample
(defun random/sample (n xs)
"Return a randomly sample of list XS of size N."
(prelude/assert (and (>= n 0) (< n (list/length xs))))
(cl-labels ((do-sample
(n xs y ys)
(if (= n (set/count ys))
(->> ys
set/to-list
(list/map (lambda (i)
(list/get i xs))))
(if (set/contains? y ys)
(do-sample n xs (random/int (list/length xs)) ys)
(do-sample n xs y (set/add y ys))))))
(do-sample n xs (random/int (list/length xs)) (set/new))))
(provide 'random)
;;; random.el ends here
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