Functional combinators and composition helpers

composition.js

// Requires utils.list.js for toList(), first(), and rest()

function tap(callback, val) {
	callback(val);
	return val;
}

function flip(fn) {
	return function() {
		return fn.apply(this, toList(arguments).reverse());
	};
}

function partial(fn, args) {
	if (arguments.length > 2 && !Array.isArray(args) && !isArguments(args)) {
		return partial(fn, rest(arguments));
	}
	
	if (!args.length) return fn;
	else return partial(fn.bind(fn, first(args)), rest(args));
}

function curry(fn, arity) {
	if (!isFunction(fn)) {
		throw new TypeError('curry() expects first argument to be a function. ' + (typeof fn) + ' given.');
	}

	arity = Number(arity || fn.length || 0);

	return function() {
		if (arguments.length >= arity) return fn.apply(this, arguments);
		else return curry(partial(fn, arguments), arity - arguments.length);
	};
}