578ed1ba98
Moving all of my Emacs-related files into their own directory at the root of this repository.
102 lines
3.1 KiB
EmacsLisp
102 lines
3.1 KiB
EmacsLisp
;;; maybe.el --- Library for dealing with nil values -*- lexical-binding: t -*-
|
|
;; Author: William Carroll <wpcarro@gmail.com>
|
|
|
|
;;; Commentary:
|
|
;; Inspired by Elm's Maybe library.
|
|
;;
|
|
;; For now, a Nothing value will be defined exclusively as a nil value. I'm
|
|
;; uninterested in supported falsiness in this module even at risk of going
|
|
;; against the LISP grain.
|
|
;;
|
|
;; I'm avoiding introducing a struct to handle the creation of Just and Nothing
|
|
;; variants of Maybe. Perhaps this is a mistake in which case this file would
|
|
;; be more aptly named nil.el. I may change that. Because of this limitation,
|
|
;; functions in Elm's Maybe library like andThen, which is the monadic bind for
|
|
;; the Maybe type, doesn't have a home here since we cannot compose multiple
|
|
;; Nothing or Just values without a struct or some other construct.
|
|
;;
|
|
;; Possible names for the variants of a Maybe.
|
|
;; None | Some
|
|
;; Nothing | Something
|
|
;; None | Just
|
|
;; Nil | Set
|
|
;;
|
|
;; NOTE: In Elisp, values like '() (i.e. the empty list) are aliases for nil.
|
|
;; What else in Elisp is an alias in this way?
|
|
;; Examples:
|
|
;; TODO: Provide examples of other nil types in Elisp.
|
|
|
|
;;; Code:
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
;; Dependencies
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
(require 'prelude)
|
|
(require 'list)
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
;; Constants
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
(defvar maybe/test? t
|
|
"When t, run the test suite defined herein.")
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
;; Library
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
(defun maybe/nil? (x)
|
|
"Return t if X is nil."
|
|
(eq nil x))
|
|
|
|
(defun maybe/some? (x)
|
|
"Return t when X is non-nil."
|
|
(not (maybe/nil? x)))
|
|
|
|
(defun maybe/nils? (&rest xs)
|
|
"Return t if all XS are nil."
|
|
(list/all? #'maybe/nil? xs))
|
|
|
|
(defun maybe/somes? (&rest xs)
|
|
"Return t if all XS are non-nil."
|
|
(list/all? #'maybe/some? xs))
|
|
|
|
(defun maybe/default (default x)
|
|
"Return DEFAULT when X is nil."
|
|
(if (maybe/nil? x) default x))
|
|
|
|
(defun maybe/map (f x)
|
|
"Apply F to X if X is not nil."
|
|
(if (maybe/some? x)
|
|
(funcall f x)
|
|
x))
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
;; Tests
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
|
|
(when maybe/test?
|
|
;; nil?
|
|
(prelude/assert (maybe/nil? nil))
|
|
(prelude/refute (maybe/nil? t))
|
|
;; some?
|
|
(prelude/assert (maybe/some? 10))
|
|
(prelude/refute (maybe/some? nil))
|
|
;; nils?
|
|
(prelude/assert (maybe/nils? nil nil nil nil))
|
|
(prelude/refute (maybe/nils? nil t nil t))
|
|
;; somes?
|
|
(prelude/assert (maybe/somes? t 10 '(1 2 3) "some"))
|
|
(prelude/refute (maybe/somes? t nil '(1 2 3) "some"))
|
|
;; default
|
|
(prelude/assert
|
|
(and (= 0 (maybe/default 5 0))
|
|
(= 5 (maybe/default 5 nil))))
|
|
;; map
|
|
(prelude/assert
|
|
(and (= 2 (maybe/map #'1+ 1))
|
|
(eq nil (maybe/map #'1+ nil)))))
|
|
|
|
(provide 'maybe)
|
|
;;; maybe.el ends here
|