import { $, HKT, I, _ } from "..";
import { ElementOf, List } from "../../list";
import { IsNever, Satisfies, Unreachable } from "../../type";
import { Fold } from ".";
type Step = [never, never, 1, 2, 3, 4, 5, 6, 7, 8, 9];
type Depth = ElementOf<Step> | true;
type DEFAULT_DEEP_OPTION_VALUE = 1;
type Options = {
    depth: Depth;
};
interface Accumulator<D extends Depth> extends HKT {
    [HKT.i]: Satisfies<_<this>, [List, unknown]>;
    [HKT.o]: I<this> extends [infer Acc extends List, infer X] ? X extends List ? IsNever<D> extends true ? [...Acc, ...X] : D extends true ? [...Acc, ...$<Flatten<{
        depth: true;
    }>, X>] : [...Acc, ...$<Flatten<{
        depth: Step[Exclude<D, true>];
    }>, X>] : [...Acc, X] : Unreachable;
}
/**
 * flattens a list, flattening nested lists to the specified depth.
 *
 * the default depth is 1 (i.e. "shallow flatten").
 * set depth to `true` to fully flatten recursive list structures
 *
 * @since 0.0.6
 */
export interface Flatten<O extends Options = {
    depth: DEFAULT_DEEP_OPTION_VALUE;
}> extends HKT {
    [HKT.i]: Satisfies<_<this>, List>;
    [HKT.o]: O extends {
        depth: infer D extends Depth;
    } ? $<Fold<Accumulator<D>, []>, I<this>> : never;
}
export {};
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