Recursive implementations of map, filter, reduce

mfr.js

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

function map(callback, list) {
	if (!list.length) return [];
	else return [callback(first(list))].concat(map(callback, rest(list)));
}

function filter(predicate, list) {
	if (!list.length) return [];
	else return (predicate(first(list)) ? [first(list)] : []).concat(filter(predicate, rest(list)));
}

function reduce(callback, value, list) {
	if (!list.length) return value;
	else return reduce(callback, callback(value, first(list)), rest(list));
}