1 files changed, 86 insertions, 0 deletions
diff --git a/users/wpcarro/emacs/.emacs.d/wpc/struct.el b/users/wpcarro/emacs/.emacs.d/wpc/struct.el
new file mode 100644
index 000000000000..35957e834449
--- /dev/null
+++ b/users/wpcarro/emacs/.emacs.d/wpc/struct.el
@@ -0,0 +1,86 @@
+;;; struct.el --- Helpers for working with structs -*- lexical-binding: t -*-
+
+;; Author: William Carroll <wpcarro@gmail.com>
+;; Version: 0.0.1
+;; URL: https://git.wpcarro.dev/wpcarro/briefcase
+;; 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:
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Dependencies
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(require 'string)
+(require 'dash)
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Library
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(defvar struct--enable-tests? t
+  "When t, run the test suite defined herein.")
+
+(defmacro struct-update (type field f xs)
+  "Apply F to FIELD in XS, which is a struct of TYPE.
+This is immutable."
+  (let ((copier (->> type
+                     symbol-name
+                     (string-prepend "copy-")
+                     intern))
+        (accessor (->> field
+                       symbol-name
+                       (string-prepend (string-concat (symbol-name type) "-"))
+                       intern)))
+    `(let ((copy (,copier ,xs)))
+       (setf (,accessor copy) (funcall ,f (,accessor copy)))
+       copy)))
+
+(defmacro struct-set (type field x xs)
+  "Immutably set FIELD in XS (struct TYPE) to X."
+  (let ((copier (->> type
+                     symbol-name
+                     (string-prepend "copy-")
+                     intern))
+        (accessor (->> field
+                       symbol-name
+                       (string-prepend (string-concat (symbol-name type) "-"))
+                       intern)))
+    `(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 (->> field
+                       symbol-name
+                       (string-prepend (string-concat (symbol-name type) "-"))
+                       intern)))
+    `(progn
+       (setf (,accessor ,xs) ,x)
+       ,xs)))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Tests
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(when struct--enable-tests?
+  (cl-defstruct dummy name age)
+  (defvar struct--test-dummy (make-dummy :name "Roofus" :age 19))
+  (struct-set! dummy name "Doofus" struct--test-dummy)
+  (prelude-assert (string= "Doofus" (dummy-name struct--test-dummy)))
+  (let ((result (struct-set dummy name "Shoofus" struct--test-dummy)))
+    ;; Test the immutability of `struct-set'
+    (prelude-assert (string= "Doofus" (dummy-name struct--test-dummy)))
+    (prelude-assert (string= "Shoofus" (dummy-name result)))))
+
+(provide 'struct)
+;;; struct.el ends here