3 files changed, 41 insertions, 12 deletions
diff --git a/users/wpcarro/emacs/pkgs/struct/default.nix b/users/wpcarro/emacs/pkgs/struct/default.nix
index 3ea514fcd6fc..3c836e74ac97 100644
--- a/users/wpcarro/emacs/pkgs/struct/default.nix
+++ b/users/wpcarro/emacs/pkgs/struct/default.nix
@@ -16,7 +16,6 @@ let
     { };
 
   emacs = (pkgs.emacsPackagesFor pkgs.emacs28).emacsWithPackages (epkgs: [
-    epkgs.dash
     struct
   ]);
 in
diff --git a/users/wpcarro/emacs/pkgs/struct/struct.el b/users/wpcarro/emacs/pkgs/struct/struct.el
index 36d9d4ac0b9e..e5b25c3836af 100644
--- a/users/wpcarro/emacs/pkgs/struct/struct.el
+++ b/users/wpcarro/emacs/pkgs/struct/struct.el
@@ -39,6 +39,16 @@ This is immutable."
        (setf (,accessor copy) (funcall ,f (,accessor copy)))
        copy)))
 
+(defmacro struct-update! (type field f xs)
+  "Mutably apply F to FIELD in XS."
+  (let ((accessor (->> field
+                       symbol-name
+                       (s-prepend (s-concat (symbol-name type) "-"))
+                       intern)))
+    `(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 (->> type
diff --git a/users/wpcarro/emacs/pkgs/struct/tests.el b/users/wpcarro/emacs/pkgs/struct/tests.el
index ee48c2f6b5d1..a7ddb52c46d6 100644
--- a/users/wpcarro/emacs/pkgs/struct/tests.el
+++ b/users/wpcarro/emacs/pkgs/struct/tests.el
@@ -3,22 +3,42 @@
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (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)
-  (should (string= "Doofus" (dummy-name struct--test-dummy))))
+(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 ()
-  (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)))
-    (should (string= "Roofus" (dummy-name struct--test-dummy)))
-    (should (string= "Shoofus" (dummy-name result)))))
+  (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)))))