feat(wpcarro/emacs): Package al, list, set, struct

Originally I set-out to package `al.el`, but as I started traversing the
dependencies, I needed to package increasingly more packages. I refactored some
of these to prune their dependencies to slay this hydra before it turned into a
never-ending project. I have mixed feelings about this.

I also introduced `ert` and unit tests into my Elisp packaging, so it'll be nice
to have build-time tests that run when Emacs updates land in depot.

Change-Id: I2756dc60888b80255a495e08ae61bd547e6b3db2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5998
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>
Tested-by: BuildkiteCI

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 =
+          (with emacsPackages; [
+            dash
+            s
+          ]);
+      })
+    { };
+
+  emacs = (pkgs.emacsPackagesFor pkgs.emacs28).emacsWithPackages (epkgs: [
+    epkgs.dash
+    struct
+  ]);
+in
+struct.overrideAttrs (_old: {
+  doCheck = true;
+  checkPhase = ''
+    ${emacs}/bin/emacs -batch \
+      -l ert -l ${./tests.el} -f ert-run-tests-batch-and-exit
+  '';
+})

users/wpcarro/emacs/pkgs/struct/struct.el

@@ -0,0 +1,68 @@
+;;; struct.el --- Helpers for working with structs -*- lexical-binding: t -*-
+
+;; Author: William Carroll <wpcarro@gmail.com>
+;; Version: 0.0.1
+;; 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 's)
+(require 'dash)
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; 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 (->> type
+                     symbol-name
+                     (s-prepend "copy-")
+                     intern))
+        (accessor (->> field
+                       symbol-name
+                       (s-prepend (s-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
+                     (s-prepend "copy-")
+                     intern))
+        (accessor (->> field
+                       symbol-name
+                       (s-prepend (s-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
+                       (s-prepend (s-concat (symbol-name type) "-"))
+                       intern)))
+    `(progn
+       (setf (,accessor ,xs) ,x)
+       ,xs)))
+
+(provide 'struct)
+;;; struct.el ends here

users/wpcarro/emacs/pkgs/struct/tests.el

@@ -0,0 +1,25 @@
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Dependencies
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(require 'ert)
+(require 'dash)
+(require 'struct)
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Tests
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(ert-deftest struct-set! ()
+  (cl-defstruct dummy name age)
+  (defvar struct--test-dummy (make-dummy :name "Roofus" :age 19))
+  (struct-set! dummy name "Doofus" struct--test-dummy)
+  (string= "Doofus" (dummy-name struct--test-dummy)))
+
+(ert-deftest struct-set ()
+  (cl-defstruct dummy name age)
+  (defvar struct--test-dummy (make-dummy :name "Roofus" :age 19))
+  (let ((result (struct-set dummy name "Shoofus" struct--test-dummy)))
+    (and
+     (string= "Roofus" (dummy-name struct--test-dummy))
+     (string= "Shoofus" (dummy-name result)))))