Flow

Module flow

Widgets, commands and the step they produce.

import ui.flow

flow is a model-update-view loop. A Widget reacts to a message and returns a Step: the next widget plus a Cmd describing the side effects to run. Commands dispatch further messages, which produce the next step, and so on. Rendering is separate: view turns a widget into a View, a tree of nodes the host draws.

Contents

• Attributes — Cmd, Widget
• Unions — View
• Data — Step
• Commands — NoCmd, BatchCmd

---

Attributes

Cmd

`flow/types.zirr:5`

attr Cmd {
    run(self: @Cmd, env: Any, dispatch: fn(@Cmd) -> Void) -> Void
}

A side effect to perform after an update. A command receives the environment it runs in and a dispatch function, so it can feed further work back into the loop instead of returning a value.

Members

Implementors

NoCmd, BatchCmd

---

Widget

`flow/types.zirr:19`

attr Widget {
    update: fn(@Widget, Any) -> Step
    view: fn(@Widget, dispatch: fn(@Cmd) -> Void) -> View
}

Anything that can handle a message and render itself. Both members are declared as function-typed fields rather than methods, so a data type adopts the attribute by naming its two functions, as in @Widget(update, view).

Members

Implementors

label.Model, textinput.Model

---

Unions

View

`flow/types.zirr:9`

union View {
	Widget
	Node
}

What a view function may return: either a nested Widget, which is rendered in turn, or a Node from the node tree.

Cases

---

Data

Step

`flow/types.zirr:14`

data Step {
	model: @Widget
	cmd: @Cmd
}

The result of an update: the widget to carry forward and the command to run. A widget that has nothing to do returns its unchanged model together with NoCmd.

Fields

---

Commands

NoCmd

`flow/commands.zirr:4`

@Cmd(fn(self, env, dispatch) { void })
data NoCmd {}

The empty command. Running it does nothing, which makes it the default second half of a Step.

---

BatchCmd

`flow/commands.zirr:11`

@Cmd(fn(self, env, dispatch) {
	for c <- self.cmds {
		Cmd(c).run(c, env, dispatch)
	}
})
data BatchCmd {
	cmds: [@Cmd]
}

Runs several commands in sequence, each with the same environment and dispatch. Order follows the list.

Fields

---

See also

• Nodes — the tree a view renders into.
• Label, Text Input — the widgets built on this loop.