;;; struct.el --- Helpers for working with structs -*- lexical-binding: t -*-
;; Author: William Carroll <wpcarro@gmail.com>
;; Version: 1.0.0
;; Package-Requires: ((emacs "24.3"))
;;; Commentary:
;; Provides new macros for working with structs. Also provides adapter
;; interfaces to existing struct macros, that should have more intuitive
;; interfaces.
;;
;; Sometimes `setf' just isn't enough.
;;; Code:
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;; Library
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(defmacro struct-update (type field f xs)
"Apply F to FIELD in XS, which is a struct of TYPE.
This is immutable."
(let ((copier (struct--copier-for type))
(accessor (struct--accessor-for type field)))
`(let ((copy (,copier ,xs)))
(setf (,accessor copy) (funcall ,f (,accessor copy)))
copy)))
(defmacro struct-update! (type field f xs)
"Mutably apply F to FIELD in XS."
(let ((accessor (struct--accessor-for type field)))
`(progn
(setf (,accessor ,xs) (funcall ,f (,accessor ,xs)))
,xs)))
(defmacro struct-set (type field x xs)
"Immutably set FIELD in XS (struct TYPE) to X."
(let ((copier (struct--copier-for type))
(accessor (struct--accessor-for type field)))
`(let ((copy (,copier ,xs)))
(setf (,accessor copy) ,x)
copy)))
(defmacro struct-set! (type field x xs)
"Set FIELD in XS (struct TYPE) to X mutably.
This is an adapter interface to `setf'."
(let ((accessor (struct--accessor-for type field)))
`(progn
(setf (,accessor ,xs) ,x)
,xs)))
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;; Helper Functions
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(defun struct--copier-for (type)
(intern (format "copy-%s" (symbol-name type))))
(defun struct--accessor-for (type field)
(intern (format "%s-%s"
(symbol-name type)
(symbol-name field))))
(provide 'struct)
;;; struct.el ends here
