Flatten

declare const alreadyFlat: Flatten<never>;

declare const flattened: <A>(value: A) => Flatten<A>;

declare const neverFlat: Flatten<never>;

declare const map: {
  <A, B>(f: (a: A) => B): (self: Flatten<A>) => Flatten<B>;
  <A, B>(self: Flatten<A>, f: (a: A) => B): Flatten<B>;
};

interface AlreadyFlat<A> extends Variance<A> {
  readonly _tag: "AlreadyFlat";
}

type Flatten<A> = Flattened<A> | AlreadyFlat<A> | NeverFlat<A>;

interface Flattened<A> extends Variance<A> {
  readonly _tag: "Flattened";
  readonly value: A;
}

interface FlattenTypeLambda extends TypeLambda {
  readonly type: Flatten<unknown>;
}

interface NeverFlat<A> extends Variance<A> {
  readonly _tag: "NeverFlat";
}

declare const isAlreadyFlat: <A>(a: Flatten<A>) => a is AlreadyFlat<A>;

declare const isFlatten: (u: unknown) => u is Flatten<unknown>;

declare const isFlattened: <A>(a: Flatten<A>) => a is Flattened<A>;

declare const isNeverFlat: <A>(a: Flatten<A>) => a is NeverFlat<A>;

declare const FlattenTypeId: unique symbol;

type FlattenTypeId = typeof FlattenTypeId;