import type { Fn, Nullable } from "@thi.ng/api";
import type { Transducer } from "./api.js";
/**
 * Transducer. Only keeps values for which (optional) predicate returns a
 * non-null result. If no `pred` is given, uses values as is.
 *
 * @param pred -
 */
export declare function keep<T>(pred?: Fn<Nullable<T>, any>): Transducer<Nullable<T>, T>;
export declare function keep<T>(src: Iterable<Nullable<T>>): IterableIterator<T>;
export declare function keep<T>(pred: Fn<Nullable<T>, any>, src: Iterable<Nullable<T>>): IterableIterator<T>;
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