89 lines
3.2 KiB
Org Mode
89 lines
3.2 KiB
Org Mode
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#+TITLE: bjogui
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Desktop programs in Bjolang, written as a model, an ~update~ and a ~view~, and
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shown with [[https://avaloniaui.net][Avalonia]].
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#+BEGIN_SRC scheme
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(import (bjogui view))
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(import (bjogui app))
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(type (: Msg (Union Inc Dec)))
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(: update (-> Msg int int))
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(defun (update msg n)
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(match msg (Inc (+ n 1)) (Dec (- n 1))))
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(: view (-> int (View Msg)))
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(defun (view n)
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(row #:spacing 8.0 #:margin 16.0
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(button "-" Dec)
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(text #"${n}")
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(button "+" Inc)))
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(defun (main)
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(run-app 0 update view #:title "Counter"))
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#+END_SRC
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A program never names an Avalonia type. A view is a Bjolang value, an event
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is a message, and the controls are made and changed by the package.
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* How it works
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An event finds its message in the view its control was last given.
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~update~ makes the next model from the message, and ~view~ makes the next
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view. The next view is compared with the last one, control by control, and
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only what differs is changed. So a control keeps its focus, its caret and its
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scroll position when the model changes.
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Children are matched by their place in the list. A child whose kind changes
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gets a new control.
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A control that is changed raises events of its own: a text input whose text
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is set says that its text changed. Those events come while the controls are
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being changed, and they are dropped, so only the user's events are messages.
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* The views: (bjogui view)
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| Constructor | Control | Sends |
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|--------------------------------------------------+--------------+-----------------------------|
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| ~(text s)~ | ~TextBlock~ | nothing |
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| ~(button label msg)~ | ~Button~ | ~msg~ on a click |
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| ~(text-input value on-input)~ | ~TextBox~ | ~(on-input text)~ on a change |
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| ~(checkbox label checked? on-toggle)~ | ~CheckBox~ | ~(on-toggle checked)~ |
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| ~(column child ...)~, ~(row child ...)~ | ~StackPanel~ | nothing |
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They take keywords where they apply: ~#:size~ (the font size of a text),
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~#:width~, ~#:height~, ~#:margin~, ~#:padding~, ~#:spacing~ (between the
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children of a column or a row), ~#:enabled~ and ~#:placeholder~. A size of
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zero, the default, leaves the size to the control.
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* Running: (bjogui app)
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- ~(run-app init update view #:title #:width #:height)~ opens a window and
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runs until it is closed.
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- ~(start-app init update view on-root)~ makes the controls with no window,
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and gives ~on-root~ the control to show. ~app-dispatch!~ sends a message,
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~app-model~ reads the model, and ~app-control-at~ finds a control by its
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path of child indices. ~tests/app.bjo~ uses these to drive an app through
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its real controls.
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* Requirements
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- Avalonia 11.3, which ~bjo~ restores from NuGet. On Linux it needs X11 or
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XWayland.
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- A Bjolang with ~(std interop)~, which makes the delegates that Avalonia's
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events take.
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* Tests
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#+BEGIN_SRC sh
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bjo run tests/app.bjo # prints "bjogui ok"
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bjo run examples/counter.bjo
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#+END_SRC
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* Not yet
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- Keyed children, for lists whose items move.
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- Messages from fibers and timers, for work that is not a click.
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- More controls: lists, grids, images, scroll views, menus.
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