;;; monoid.el --- Working with Monoids in Elisp -*- lexical-binding: t -*- ;; Author: William Carroll <wpcarro@gmail.com> ;;; Commentary: ;; The day has finally arrived where I'm using Monoids in Elisp. ;; ;; The monoid typeclass is as follows: ;; - empty :: a ;; - concat :: (list a) -> a ;;; Code: ;; TODO: Consider a prelude version that works for all Elisp types. (defun monoid/classify (xs) "Return the type of `XS'." (cond ((listp xs) 'list) ((vectorp xs) 'vector) ((stringp xs) 'string))) (defun monoid/empty (xs) "Return the empty monoid for the type `XS'." (pcase (monoid/classify xs) ('list '()) ('vector []) ('string ""))) (provide 'monoid) ;;; monoid.el ends here