JavaScript Tuple Implementation

Tuple.js

/* 
 *  Tuple.js - JavaScript Tuple Implmentation
 *  ------------------------------------------------
 *  The Tuple object is an immutable, fixed-length
 *  structure used to hold a heterogeneous set of n
 *  typed values that can be used for inter-function
 *  communication. For instance, you can use it to 
 *  build quick value objects.
 *  
 *  Borrowed from 'Functional Programming in Javascript'.
 *
 */

const Tuple = function( /* Types */ ) {

	// Reads provided argument types the tuple will contain.
	const typeInfo = Array.prototype.slice.call(arguments, 0);

	/*
	Declares an internal type _T in charge of making sure
	the types match the corresponding values.
	*/
	const _T = function( /* Values */ ) {
		// Extracts values to be stored in the tuple.
		const values = Array.prototype.slice.call(arguments, 0);

		// Check for non-null values.
		if(values.some((val) => val === null || val === undefined)) {
			throw new ReferenceError('Tuples may not have any null values');
		}

		/*
		Check that the tuple has the correct arity with
		respect to the number of types defined.
		*/
		if(values.length !== typeInfo.length) {
			throw new TypeError('Tuple arity does not match its prototype');
		}

		/*
		Check that each value passed in matches the correct type in 
		the tuple definition using the checkType function.  Every 
		tuple element will translate to a roperty of the tuple 
		referred to by ._n, where n is the index  of the element 
		(starting at 1). 
		*/
		values.map(function(val, index) {
			this['_' + (index + 1)] = checkType(typeInfo[index])(val);
		}, this);

		Object.freeze(this);
	};

	/*
	Extracts all the values from the tuple as an array.  You can use
	this with ES6 assignment destructuring to map tuple values into 
	variables. 
	*/
	_T.prototype.values = function() {
		return Object.keys(this).map(function(k) {
			return this[k];
		}, this);
	};

	return _T;

};