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+;;; 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:
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Library
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(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)))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Helper Functions
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(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