Types & Protocols

Milo's type system uses frozen dataclasses for immutability and protocols for structural typing. All types use@dataclass(frozen=True, slots=True)for immutability and memory efficiency.

Core types

Type	Description
`Action(type, payload)`	Frozen dataclass. Dispatched to reducers.
`Key(char, name, ctrl, alt, shift)`	Frozen dataclass. Represents a keypress.
`ReducerResult(state, sagas, cmds, view)`	Returned by reducers to schedule side effects.
`Quit(state, code, sagas, cmds, view)`	Signal the app to exit. Return from a reducer to stop the event loop.
`ViewState(alt_screen, cursor_visible, window_title, mouse_mode)`	Declarative terminal state. The renderer diffs previous vs. current and applies only changes.
`FieldSpec(name, label, field_type, choices, default, validator, placeholder)`	Declarative form field configuration.
`FieldState(value, cursor, error, focused)`	Runtime state of a single form field.
`FormState(fields, specs, current, submitted)`	Runtime state of an entire form.
`Screen(name, template, reducer)`	A flow screen definition.
`Transition(from_screen, to_screen, on)`	A flow transition rule.
`FlowState(current_screen, screen_states)`	Runtime state of a multi-screen flow.

Saga effect types

Type	Description
`Call(fn, args, kwargs)`	Call a function, receive its return value.
`Put(action)`	Dispatch an action to the store.
`Select(selector)`	Read current state or a slice.
`Fork(saga)`	Launch a concurrent child saga.
`Delay(seconds)`	Sleep for a duration.
`Retry(fn, args, kwargs, max_attempts, backoff, base_delay, max_delay)`	Call with retry and backoff on failure.

Command types

Lightweight alternatives to sagas for one-shot effects. See Commands for usage.

Type	Description
`Cmd(fn)`	A thunk`() -> Action \| None`. Runs on the thread pool, dispatches the returned action.
`Batch(cmds)`	Run commands concurrently with no ordering guarantees.
`Sequence(cmds)`	Run commands serially, in order. Each result is dispatched before the next starts.
`TickCmd(interval)`	Schedule a single`@@TICK` after interval seconds. Return another from `@@TICK`to keep ticking.
`compact_cmds(*cmds)`	Helper: strips`None`entries from a command tuple.

Enums

UP, DOWN, LEFT, RIGHT, HOME, END, PAGE_UP, PAGE_DOWN, INSERT, DELETE, BACKSPACE, TAB, ENTER, ESCAPE, F1–F12

TEXT, PASSWORD, SELECT, CONFIRM

Enum	Description
`AppStatus`	Application lifecycle states
`RenderTarget`	Render output targets
`ErrorCode`	All namespaced error codes

Protocols

Protocol	Signature
`Reducer`	`(state, Action) -> state \| ReducerResult \| Quit`
`Saga`	`Generator[effect, result, None]`
`DispatchFn`	`(Action) -> None`
`GetStateFn`	`() -> state`
`Middleware`	`(DispatchFn, GetStateFn) -> DispatchFn`
`FieldValidator`	`(str) -> str \| None`

Note

Protocols use structural typing — your functions and classes don't need to explicitly inherit from them. If the signature matches, it satisfies the protocol.