haskell applicative function in js

applicative.js

function callFn(f, ...args) {
    if (f.length === 0) {
        return f();
    }
    if (f.length === args.length) {
        return f(...args);
    }
    if (f.length > args.length) {
        const ret = f.bind(null, ...args);
        ret.fn_name = `(${f.fn_name}(bind))`;
        return ret;
    }
    // TODO <
    throw new Error('TODO')
}

function applicativeFn(f, g) {
    const ret = (x) => {
        return callFn(callFn(f, x), callFn(g, x));
    };
    ret.fn_name = `(${f.fn_name} + ${g.fn_name})`;
    return ret;
}

const pure = (f) => {
    const ret = () => f;
    ret.fn_name = `${f.fn_name}(pure)`;
    return ret;
};

const plusFn = (a, b) => a + b;

plusFn.fn_name = 'plusFn';

const plus3 = (a) => a + 3;

plus3.fn_name = 'plus3';

const mul100 = (a) => a * 100;

mul100.fn_name = 'mul100';


// (+) <$> (+3) <*> (*100) $ 5
const fn = applicativeFn(applicativeFn(pure(plusFn), plus3), mul100);
console.log(fn(5));


// (+) <*> (+3) $ 2
const fn3 = applicativeFn(plusFn, plus3);
console.log(fn3(2));