/**
 * Scope operator for reducer composition.
 *
 * The scope() function embeds a child reducer into a parent reducer by:
 * 1. Extracting child state from parent state
 * 2. Running the child reducer
 * 3. Embedding the result back into parent state
 * 4. Lifting child effects to parent actions
 */
import type { Reducer } from '../types.js';
/**
 * Lens for extracting child state from parent state.
 */
export type StateLens<ParentState, ChildState> = (parent: ParentState) => ChildState;
/**
 * Function to update parent state with new child state.
 */
export type StateUpdater<ParentState, ChildState> = (parent: ParentState, child: ChildState) => ParentState;
/**
 * Prism for extracting child action from parent action.
 * Returns null if parent action doesn't apply to child.
 */
export type ActionPrism<ParentAction, ChildAction> = (parent: ParentAction) => ChildAction | null;
/**
 * Function to embed child action in parent action.
 */
export type ActionEmbedder<ParentAction, ChildAction> = (child: ChildAction) => ParentAction;
/**
 * Scope a child reducer to work with parent state and actions.
 * This is the core composition primitive.
 *
 * @param toChildState - Extract child state from parent state
 * @param fromChildState - Embed child state back into parent state
 * @param toChildAction - Extract child action from parent action (returns null if not applicable)
 * @param fromChildAction - Wrap child action into parent action
 * @param childReducer - The child reducer to compose
 * @returns A parent reducer
 *
 * @example
 * ```typescript
 * const parentReducer = scope(
 *   (parent: AppState) => parent.counter,
 *   (parent, child) => ({ ...parent, counter: child }),
 *   (action: AppAction) => action.type === 'counter' ? action.action : null,
 *   (childAction) => ({ type: 'counter', action: childAction }),
 *   counterReducer
 * );
 * ```
 */
export declare function scope<ParentState, ParentAction, ChildState, ChildAction, Dependencies = any>(toChildState: StateLens<ParentState, ChildState>, fromChildState: StateUpdater<ParentState, ChildState>, toChildAction: ActionPrism<ParentAction, ChildAction>, fromChildAction: ActionEmbedder<ParentAction, ChildAction>, childReducer: Reducer<ChildState, ChildAction, Dependencies>): Reducer<ParentState, ParentAction, Dependencies>;
/**
 * Helper for common case where child actions are embedded in parent actions.
 *
 * @param toChildState - Extract child state from parent state
 * @param fromChildState - Embed child state back into parent state
 * @param actionType - The action type string to match
 * @param childReducer - The child reducer to compose
 * @returns A parent reducer
 *
 * @example
 * ```typescript
 * type AppAction = { type: 'counter'; action: CounterAction } | ...;
 *
 * const parentReducer = scopeAction(
 *   (parent: AppState) => parent.counter,
 *   (parent, child) => ({ ...parent, counter: child }),
 *   'counter',
 *   counterReducer
 * );
 * ```
 */
export declare function scopeAction<ParentState, ParentAction extends {
    type: string;
}, ChildState, ChildAction, Dependencies = any>(toChildState: StateLens<ParentState, ChildState>, fromChildState: StateUpdater<ParentState, ChildState>, actionType: string, childReducer: Reducer<ChildState, ChildAction, Dependencies>): Reducer<ParentState, ParentAction, Dependencies>;
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