path: root/emacs/.emacs.d/wpc/dotted.el

;;; dotted.el --- Working with dotted pairs in Elisp -*- lexical-binding: t -*-
;; Author: William Carroll <wpcarro@gmail.com>

;;; Commentary:
;; Part of my primitives library extensions in Elisp.  Contrast my primitives
;; with the wrapper extensions that I provide, which expose immutable variants
;; of data structures like an list, alist, tuple, as well as quasi-typeclasses
;; like sequence, etc.

;;; Code:

(require 'prelude)
(require 'macros)

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;; Library
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(cl-defun dotted/new (&optional a b)
  "Create a new dotted pair (i.e. cons cell)."
  (cons a b))

(defun dotted/instance? (x)
  "Return t if X is a dotted pair."
  (let ((b (cdr x)))
    (and b (atom b))))

(defun dotted/first (x)
  "Return the first element of X."
  (car x))

(defun dotted/second (x)
  "Return the second element of X."
  (cdr x))

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;; Tests
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(progn
  (prelude-assert
   (equal '(fname . "Bob") (dotted/new 'fname "Bob")))
  (prelude-assert
   (dotted/instance? '(one . two)))
  (prelude-refute
   (dotted/instance? '(1 2 3))))

(provide 'dotted)
;;; dotted.el ends here