functional-data-structure/finger-tree

import assert from 'assert';

import {CachedMeasure} from '../0-core/index.js';

import {Node2} from './2-Node2.js';
import {Node3} from './3-Node3.js';

export function node3(M, a, b, c) {
    assert(
        !(a instanceof Node2 || a instanceof Node3) || M instanceof CachedMeasure,
    );
    assert(
        a instanceof Node2 || a instanceof Node3 || !(M instanceof CachedMeasure),
    );
    return new Node3(
        M.plus(M.measure(a), M.plus(M.measure(b), M.measure(c))),
        a,
        b,
        c,
    );
}