export type Operator<T, U> = Operator.fλ<T, U> | ((data: U) => boolean) | (U extends T ? (data: T) => data is U : never) ;
export namespace Operator {
export type fλ<T, U> = fλ.Stateless<T, U> | fλ.Stateful<T, U> ;
export namespace fλ {
export type Stateless<T, U> = (data: T, registerSideEffect: (sideEffect: () => void) => void) => readonly [U] | null;
export type Stateful<T, U> = [ (data: T, prev: U, registerSideEffect: (sideEffect: () => void)=> void) => readonly [U] | null, U ];
}
export type Stateless<T, U> = fλ.Stateless<T, U> | ((data: U) => boolean) | (U extends T ? (data: T) => data is U : never) ;
}