A todo example, and its picture in the Readme

run-app takes #:screenshot, a path: the window saves a PNG of itself there
once it is shown and laid out, at twice its size, and closes. It defaults to
the environment variable BJOGUI_SCREENSHOT, so any program can be pictured
with no change. docs/todo.png is examples/todo.bjo, taken that way.

🤖 Generated with [ECA](https://eca.dev) (anthropic/claude-opus-4-8)

Co-Authored-By: eca-agent <git@eca.dev>

examples/todo.bjo

@@ -0,0 +1,103 @@
+;; This Source Code Form is subject to the terms of the Mozilla Public
+;; License, v. 2.0. If a copy of the MPL was not distributed with this
+;; file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+;; bjogui/examples/todo.bjo — a todo list.
+;;
+;;     bjo run examples/todo.bjo
+;;
+;; The picture in the Readme is this program, taken with
+;;
+;;     BJOGUI_SCREENSHOT=docs/todo.png bjo run examples/todo.bjo
+
+(import (std prelude))
+(import (bjogui view))
+(import (bjogui app))
+
+(type (: Todo (Record (: id int) (: title string) (: done bool))))
+
+(type (: Msg (Union (: Typed string) Add (: Toggle int bool) (: Chose int)
+                    ClearDone (: Tab int) (: Size double))))
+
+(type (: Model (Record (: todos (List Todo)) (: draft string) (: next-id int)
+                       (: chosen int) (: tab int) (: size double))))
+
+(: gui-update (-> Msg Model (Tuple Model (List (Event Msg)))))
+(defun (gui-update msg m)
+  (next
+    (match msg
+      ((Typed s) (record-set m (draft s)))
+      (Add
+       (if (string-empty? (.draft m))
+           m
+           (record-set m (todos (list-append (.todos m)
+                                             (list (Todo (id (.next-id m)) (title (.draft m))
+                                                         (done #f)))))
+                         (draft "")
+                         (next-id (+ (.next-id m) 1)))))
+      ((Toggle id done)
+       (record-set m (todos (list-map (fun (t) (if (= (.id t) id) (record-set t (done done)) t))
+                                      (.todos m)))))
+      ((Chose i) (record-set m (chosen i)))
+      (ClearDone (record-set m (todos (list-filter (fun (t) (not (.done t))) (.todos m)))
+                               (chosen -1)))
+      ((Tab i) (record-set m (tab i)))
+      ((Size d) (record-set m (size d))))))
+
+(: (-> Model int))
+(defun (done-count m)
+  (length (list-filter (fun (t) (.done t)) (.todos m))))
+
+(: (-> Model double Todo (View Msg)))
+(defun (todo-row m size t)
+  (keyed (int->string (.id t))
+         (row #:spacing 8.0
+           (checkbox "" (.done t) (fun (b) (Toggle (.id t) b)))
+           (if (.done t)
+               (paint (text (.title t) #:size size) #:colour "#7f8c8d")
+               (text (.title t) #:size size)))))
+
+(: (-> Model (View Msg)))
+(defun (todo-tab m)
+  (def total (length (.todos m)))
+  (column #:spacing 10.0 #:margin 12.0
+    (grid #:columns "*,Auto" #:spacing 8.0
+      (at 0 0 (text-input (.draft m) Typed #:placeholder "What needs doing?"))
+      (at 0 1 (paint (button "Add" Add #:enabled (not (string-empty? (.draft m))))
+                     #:background "#27ae60" #:colour "white")))
+    (list-box (vec-map (fun (t) (todo-row m (.size m) t)) (list->vec (.todos m)))
+              (.chosen m) Chose #:height 218.0)
+    (grid #:columns "*,Auto" #:spacing 8.0
+      (at 0 0 (column #:spacing 4.0
+                (text #"${(done-count m)} of ${total} done")
+                (progress-bar (if (= total 0) 0.0
+                                  (/ (cast System.Double (done-count m)) (cast System.Double total))))))
+      (at 0 1 (button "Clear done" ClearDone #:enabled (> (done-count m) 0))))))
+
+(: (-> Model (View Msg)))
+(defun (settings-tab m)
+  (column #:spacing 10.0 #:margin 12.0
+    (text "Text size")
+    (slider (.size m) 10.0 24.0 Size)
+    (border (text "Written in Bjolang, drawn by Avalonia." #:wrap #t)
+            #:colour "#2980b9" #:radius 6.0 #:background "#ecf0f1" #:padding 10.0)))
+
+(: (-> Model (View Msg)))
+(defun (view m)
+  (column #:margin 8.0
+    (paint (text "Things to do" #:size 22.0 #:margin 6.0) #:colour "#2c3e50")
+    (tabs (.tab m) Tab
+      (tab "List" (todo-tab m))
+      (tab "Settings" (settings-tab m)))))
+
+(: (-> string bool int Todo))
+(defun (todo title done id) (Todo (id id) (title title) (done done)))
+
+(defun (main)
+  (run-app (Model (todos (list (todo "Buy milk" #t 1)
+                               (todo "Write the bjogui Readme" #t 2)
+                               (todo "Add menus and dialogs" #f 3)
+                               (todo "Walk the dog" #f 4)))
+                  (draft "Water the plants") (next-id 5) (chosen 2) (tab 0) (size 14.0))
+           gui-update view
+           #:title "bjogui todo" #:width 420.0 #:height 450.0))