distinctUntilChange - TypeScript extend Most.js

most_custom.ts

import { Stream } from "most";
import * as R from "ramda";

declare module "most" {
    interface Stream<A> {
        distinctUntilChange<T>(seed: T): Stream<T>;
    }
}

const pairs = <P, C>(prev: P, current: C) => ({ seed: current, value: [prev, current] });

function distinctUntilChange<T>(stream: Stream<T>, seed: T) {
    return stream
        .loop<T, T[]>(pairs, seed)
        .filter(p => !R.equals(p[0], p[1]))
        .map(p => p[1]);
}

Stream.prototype.distinctUntilChange = function<T>(seed: T) {
    return distinctUntilChange(this, seed);
};