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;;; tuple.el --- Tuple API for Elisp -*- lexical-binding: t -*-
;; Author: William Carroll <wpcarro@gmail.com>
;; Version: 0.0.1
;; Package-Requires: ((emacs "25.1"))
;;; Commentary:
;; Work with cons cells with two elements with a familiar API for those who have
;; worked with tuples before.
;;; Code:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Library
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(cl-defstruct tuple first second)
;; Create
(defun tuple-new ()
"Return an empty tuple."
(make-tuple :first nil
:second nil))
(defun tuple-from (a b)
"Return a new tuple from A and B."
(make-tuple :first a
:second b))
(defun tuple-from-dotted (dp)
"Convert dotted pair, DP, into a tuple."
(tuple-from (car dp) (cdr dp)))
;; Read
(defun tuple-first (pair)
"Return the first element of PAIR."
(tuple-first pair))
(defun tuple-second (pair)
"Return the second element of PAIR."
(tuple-second pair))
;; Update
(defun tuple-map-each (f g pair)
"Apply F to first, G to second in PAIR."
(->> pair
(tuple-map-first f)
(tuple-map-second g)))
(defun tuple-map (f pair)
"Apply F to PAIR."
(let ((pair-copy (copy-tuple pair)))
(funcall f pair-copy)))
(defun tuple-map-first (f pair)
"Apply function F to the first element of PAIR."
(let ((pair-copy (copy-tuple pair)))
(setf (tuple-first pair-copy) (funcall f (tuple-first pair-copy)))
pair-copy))
(defun tuple-map-second (f pair)
"Apply function F to the second element of PAIR."
(let ((pair-copy (copy-tuple pair)))
(setf (tuple-second pair-copy) (funcall f (tuple-second pair-copy)))
pair-copy))
(defun tuple-set-first (a pair)
"Return a new tuple with the first element set as A in PAIR."
(tuple-map-first (lambda (_) a) pair))
(defun tuple-set-second (b pair)
"Return a new tuple with the second element set as B in PAIR."
(tuple-map-second (lambda (_) b) pair))
;; Delete
(defun tuple-delete-first (pair)
"Return PAIR with the first element set to nil."
(tuple-set-first nil pair))
(defun tuple-delete-second (pair)
"Return PAIR with the second element set to nil."
(tuple-set-second nil pair))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Predicates
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defun tuple-instance? (x)
"Return t if X is a tuple."
(tuple-p x))
(provide 'tuple)
;;; tuple.el ends here
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