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Diffstat (limited to 'users/wpcarro/emacs/.emacs.d/wpc/maybe.el')
-rw-r--r-- | users/wpcarro/emacs/.emacs.d/wpc/maybe.el | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/users/wpcarro/emacs/.emacs.d/wpc/maybe.el b/users/wpcarro/emacs/.emacs.d/wpc/maybe.el new file mode 100644 index 000000000000..ef92e5a4c15c --- /dev/null +++ b/users/wpcarro/emacs/.emacs.d/wpc/maybe.el @@ -0,0 +1,78 @@ +;;; maybe.el --- Library for dealing with nil values -*- lexical-binding: t -*- + +;; Author: William Carroll <wpcarro@gmail.com> +;; Version: 0.0.1 +;; Package-Requires: ((emacs "24")) + +;;; 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 'list) + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; Constants +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +(defvar maybe--run-tests? 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)) + +(provide 'maybe) +;;; maybe.el ends here |