4 files changed, 144 insertions, 0 deletions
diff --git a/users/wpcarro/emacs/pkgs/struct/README.md b/users/wpcarro/emacs/pkgs/struct/README.md
new file mode 100644
index 000000000000..34dac6614cd1
--- /dev/null
+++ b/users/wpcarro/emacs/pkgs/struct/README.md
@@ -0,0 +1,6 @@
+# struct.el
+
+[![Build status](https://badge.buildkite.com/016bff4b8ae2704a3bbbb0a250784e6692007c582983b6dea7.svg?branch=refs/heads/canon)](https://buildkite.com/tvl/depot)
+
+Provides new macros exposing immutable and mutable interfaces for working with
+structs in Elisp.
diff --git a/users/wpcarro/emacs/pkgs/struct/default.nix b/users/wpcarro/emacs/pkgs/struct/default.nix
new file mode 100644
index 000000000000..558ebd0a3d20
--- /dev/null
+++ b/users/wpcarro/emacs/pkgs/struct/default.nix
@@ -0,0 +1,29 @@
+{ pkgs, depot, ... }:
+
+let
+  struct = pkgs.callPackage
+    ({ emacsPackages }:
+      emacsPackages.trivialBuild {
+        pname = "struct";
+        version = "1.0.0";
+        src = ./struct.el;
+        packageRequires = [ ];
+      })
+    { };
+
+  emacs = (pkgs.emacsPackagesFor pkgs.emacs28).emacsWithPackages (epkgs: [
+    struct
+  ]);
+in
+struct.overrideAttrs (_old: {
+  doCheck = true;
+  checkPhase = ''
+    ${emacs}/bin/emacs -batch \
+      -l ert -l ${./tests.el} -f ert-run-tests-batch-and-exit
+  '';
+  passthru.meta.ci.extraSteps.github = depot.tools.releases.filteredGitPush {
+    filter = ":/users/wpcarro/emacs/pkgs/struct";
+    remote = "git@github.com:wpcarro/struct.el.git";
+    ref = "refs/heads/canon";
+  };
+})
diff --git a/users/wpcarro/emacs/pkgs/struct/struct.el b/users/wpcarro/emacs/pkgs/struct/struct.el
new file mode 100644
index 000000000000..5d6572bf6dde
--- /dev/null
+++ b/users/wpcarro/emacs/pkgs/struct/struct.el
@@ -0,0 +1,65 @@
+;;; 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
diff --git a/users/wpcarro/emacs/pkgs/struct/tests.el b/users/wpcarro/emacs/pkgs/struct/tests.el
new file mode 100644
index 000000000000..a7ddb52c46d6
--- /dev/null
+++ b/users/wpcarro/emacs/pkgs/struct/tests.el
@@ -0,0 +1,44 @@
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Dependencies
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(require 'ert)
+(require 'struct)
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Tests
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(cl-defstruct dummy name age)
+
+(ert-deftest struct-update ()
+  (let* ((test (make-dummy :name "Roofus" :age 19))
+         (result (struct-update dummy name #'upcase test)))
+    ;; test
+    (should (string= "Roofus" (dummy-name test)))
+    (should (= 19 (dummy-age test)))
+    ;; result
+    (should (string= "ROOFUS" (dummy-name result)))
+    (should (= 19 (dummy-age result)))))
+
+(ert-deftest struct-update! ()
+  (let ((test (make-dummy :name "Roofus" :age 19)))
+    (struct-update! dummy name #'upcase test)
+    (should (string= "ROOFUS" (dummy-name test)))
+    (should (= 19 (dummy-age test)))))
+
+(ert-deftest struct-set ()
+  (let* ((test (make-dummy :name "Roofus" :age 19))
+         (result (struct-set dummy name "Shoofus" test)))
+    ;; test
+    (should (string= "Roofus" (dummy-name test)))
+    (should (= 19 (dummy-age test)))
+    ;; result
+    (should (string= "Shoofus" (dummy-name result)))
+    (should (= 19 (dummy-age result)))))
+
+(ert-deftest struct-set! ()
+  (let ((test (make-dummy :name "Roofus" :age 19)))
+    (struct-set! dummy name "Doofus" test)
+    (should (string= "Doofus" (dummy-name test)))
+    (should (= 19 (dummy-age test)))))