3 files changed, 95 insertions, 25 deletions
diff --git a/users/wpcarro/emacs/.emacs.d/wpc/bag.el b/users/wpcarro/emacs/pkgs/bag/bag.el
index 467e25fceb65..502f5672536e 100644
--- a/users/wpcarro/emacs/.emacs.d/wpc/bag.el
+++ b/users/wpcarro/emacs/pkgs/bag/bag.el
@@ -8,7 +8,7 @@
 ;; What is a bag?  A bag should be thought of as a frequency table.  It's a way
 ;; to convert a list of something into a set that allows duplicates.  Isn't
 ;; allowing duplicates the whole thing with Sets?  Kind of.  But the interface
-;; of Sets is something that bags resemble, so multi-set isn't as bag of a name
+;; of Sets is something that bags resemble, so multi-set isn't as bad of a name
 ;; as it may first seem.
 ;;
 ;; If you've used Python's collections.Counter, the concept of a bag should be
@@ -27,7 +27,7 @@
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (require 'al)
-(require 'number)
+(require 'list)
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Library
@@ -35,36 +35,44 @@
 
 (cl-defstruct bag xs)
 
-(defun bag-update (f xs)
-  "Call F on alist in XS."
-  (let ((ys (bag-xs xs)))
-    (setf (bag-xs xs) (funcall f ys))))
-
 (defun bag-new ()
   "Create an empty bag."
   (make-bag :xs (al-new)))
 
-(defun bag-contains? (x xs)
-  "Return t if XS has X."
-  (al-has-key? x (bag-xs xs)))
-
-;; TODO: Tabling this for now since working with structs seems to be
-;; disappointingly difficult.  Where is `struct-update'?
-;; (defun bag-add (x xs)
-;;   "Add X to XS.")
-
-;; TODO: What do we name delete vs. remove?
-;; (defun bag-remove (x xs)
-;;   "Remove X from XS.
-;; This is a no-op is X doesn't exist in XS.")
-
 (defun bag-from-list (xs)
   "Map a list of `XS' into a bag."
   (->> xs
-       (list-reduce
-        (bag-new)
-        (lambda (x acc)
-          (bag-add x 1 #'number-inc acc)))))
+       (list-reduce (bag-new) #'bag-add)))
+
+(defun bag-add (x xs)
+  "Add X to XS."
+  (if (bag-contains? x xs)
+      (struct-update
+       bag xs (lambda (xs) (al-update x (lambda (x) (+ 1 x)) xs)) xs)
+    (struct-update bag xs (lambda (xs) (al-set x 1 xs)) xs)))
+
+(defun bag-remove (x xs)
+  "Remove X from XS.
+This is a no-op is X doesn't exist in XS."
+  (when (bag-contains? x xs)
+    (struct-update bag xs (lambda (xs) (al-delete x xs)) xs)))
+
+(defun bag-count (x xs)
+  "Return the number of occurrences of X in XS."
+  (al-get x (bag-xs xs) 0))
+
+(defun bag-total (xs)
+  "Return the total number of elements in XS."
+  (->> (bag-xs xs)
+       (al-reduce 0 (lambda (_key v acc) (+ acc v)))))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Predicates
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(defun bag-contains? (x xs)
+  "Return t if XS has X."
+  (al-has-key? x (bag-xs xs)))
 
 (provide 'bag)
 ;;; bag.el ends here
diff --git a/users/wpcarro/emacs/pkgs/bag/default.nix b/users/wpcarro/emacs/pkgs/bag/default.nix
new file mode 100644
index 000000000000..3dedc27286d1
--- /dev/null
+++ b/users/wpcarro/emacs/pkgs/bag/default.nix
@@ -0,0 +1,26 @@
+{ pkgs, depot, ... }:
+
+let
+  bag = pkgs.callPackage
+    ({ emacsPackages }:
+      emacsPackages.trivialBuild {
+        pname = "bag";
+        version = "1.0.0";
+        src = ./bag.el;
+        packageRequires =
+          (with depot.users.wpcarro.emacs.pkgs; [
+            al
+            list
+          ]);
+      })
+    { };
+
+  emacs = (pkgs.emacsPackagesFor pkgs.emacs28).emacsWithPackages (epkgs: [ bag ]);
+in
+bag.overrideAttrs (_old: {
+  doCheck = true;
+  checkPhase = ''
+    ${emacs}/bin/emacs -batch \
+      -l ert -l ${./tests.el} -f ert-run-tests-batch-and-exit
+  '';
+})
diff --git a/users/wpcarro/emacs/pkgs/bag/tests.el b/users/wpcarro/emacs/pkgs/bag/tests.el
new file mode 100644
index 000000000000..0cc2a6029e3c
--- /dev/null
+++ b/users/wpcarro/emacs/pkgs/bag/tests.el
@@ -0,0 +1,36 @@
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Dependencies
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(require 'ert)
+(require 'bag)
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Tests
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(setq fixture (bag-from-list '(1 1 1 2 2 3)))
+
+(ert-deftest bag-add ()
+  (and
+   (not (bag-contains? 4 fixture))
+   (bag-contains? 4 (bag-add 4 fixture))))
+
+(ert-deftest bag-remove ()
+  (and
+   (bag-contains? 1 fixture)
+   (not (bag-contains? 3 (bag-remove 3 fixture)))))
+
+(ert-deftest bag-count ()
+  (and
+   (= 3 (bag-count 1 fixture))
+   (= 2 (bag-count 2 fixture))
+   (= 1 (bag-count 3 fixture))))
+
+(ert-deftest bag-total ()
+  (= 6 (bag-total fixture)))
+
+(ert-deftest bag-contains? ()
+  (and
+   (bag-contains? 1 fixture)
+   (not (bag-contains? 4 fixture))))