curry.es6.js

const curry = (fn) => {
    var a = [];

    var $curry = (...args) => {
        var tooManyArgsException = n =>
            `too many args exception: curry expected ${fn.length} args; found ${n} args`;

        a = [...a, ...args];

        // reset if already has fulfilled arity requirement
        a = a.length > fn.length ? args : a;

        if (a.length > fn.length) {
            throw tooManyArgsException(a.length);
        }

        if (a.length < fn.length) {
            return $curry;
        }

        return fn(...a);
    }

    return $curry;
};