functional-abstraction/measure

/**
 * Abstract Measure class.
 */
export class Measure {
    /**
     * Constructor, stores the monoid.
     */
    constructor(monoid) {
        this.monoid = monoid;
    }

    /**
     * Returns the zero measure according to the monoid.
     */
    zero() {
        return this.monoid.zero();
    }

    /**
     * Adds measures together using monoid#plus.
     */
    plus(a, b, c = undefined) {
        if (c === undefined) return this.monoid.plus(a, b);

        return this.monoid.plus(a, this.monoid.plus(b, c));
    }

    /**
     * Returns the measure of an element. Must be implemented by classes
     * extending Measure
     */
    measure(_element) {
        throw new Error('measure : not implemented');
    }
}