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Commands and subscriptions, and gui-update

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gui-update is a plain function, so it cannot wait. It returns the work to do
as values. A command is an (Event %m), synced in a fiber of its own, whose
answer is the next message. A subscription is a source of messages that the
model asks for: after each update the app starts the new ones and cancels the
ones that are gone, by key. every sends a message on a timer, and
subscription takes a source of one's own.

The fibers belong to the app's scope and post their messages to the UI
thread, so gui-update and view only run there. Closing the window cancels
them. The prelude's path macros already use the name update, hence
gui-update.

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

Co-Authored-By: eca-agent <git@eca.dev>
This commit is contained in:
Linus Björnstam 2026-10-25 17:02:02 +01:00
parent 2f4c99ba62
commit 4f48282314
6 changed files with 460 additions and 67 deletions
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15
examples/counter.bjo
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@ -13,12 +13,13 @@
(type (: Msg (Union Inc Dec (: Typed string))))
(type (: Model (Record (: count int) (: name string))))
(: update (-> Msg Model Model))
(defun (update msg m)
(match msg
(Inc (record-set m (count (+ (.count m) 1))))
(Dec (record-set m (count (- (.count m) 1))))
((Typed s) (record-set m (name s)))))
(: gui-update (-> Msg Model (Tuple Model (List (Event Msg)))))
(defun (gui-update msg m)
(next
(match msg
(Inc (record-set m (count (+ (.count m) 1))))
(Dec (record-set m (count (- (.count m) 1))))
((Typed s) (record-set m (name s))))))
(: view (-> Model (View Msg)))
(defun (view m)
@ -31,4 +32,4 @@
(button "+" Inc #:width 40.0))))
(defun (main)
(run-app (Model (count 0) (name "")) update view #:title "Counter" #:width 320.0 #:height 200.0))
(run-app (Model (count 0) (name "")) gui-update view #:title "Counter" #:width 320.0 #:height 200.0))