var sys = require("sys");

set = function(a) {
	return function() {
		return a.length
				? a.shift()
				: null
	}
}
exports.set = set;

zipWith = function(a) {
	return function(itA) {
		return function(itB) {
			return map(function(n) {
				return a(n)(itB());
			})(itA)
		}
	}
}
exports.zipWith = zipWith;

foldr = function(a) {
	return function(b) {
		return function(it) {
			return function() {
				var n = it();
				return null === n
						? b
						: a(n)(arguments.callee())
			}()
		}
	}
}
exports.foldr = foldr;

quot = function(a) {
	return function(b) {
		return b == null ? parseInt(a) : parseInt(parseInt(a) / parseInt(b))
	}
}
exports.quot = quot;

sum = function(a) {
	return function(b) {
		return b == null ? a : a + b
	}
}
exports.sum = sum;

scale = function(a) {
	return function(b) {
		return b == null
				? parseInt(a)
				: parseInt(a) * parseInt(b)
	}
}
exports.scale = scale;

fib = function() {
	var n = 0;
	var f = memoize(function(n) {
		return n == 0
				? 0
				: (n == 1
					? 1
					: f(n-1) + f(n-2))
	});
	return function() {
		return f(n++)
	}
}
exports.fib = fib;

nat = function() {
	var n = 0
	return function() {
		return n++
	}
}
exports.nat = nat;

map = function(a) {
	return function(it) {
		return function() {
			var n = it();
			return null === n
					? null
					: a(n)
		}
	}
}
exports.map = map;

takeWhile = function(pred) {
	return function(it) {
		return function() {
			var n = it();
			return pred(n)
					? n
					: null
		}
	}
}
exports.takeWhile = takeWhile;

take = function(n) {
	return function(it) {
		return function() {
			return n-- > 0
					? it()
					: null
		}
	}
}
exports.take = take;

filter = function(predicate) {
	return function(it) {
		return function() {
			var n = it();
			return null === n
					? null
					: (predicate(n)
						? n
						: arguments.callee())
		}
	}
}
exports.filter = filter;

isMultipleOf = function(n) {
	return function(m) {
		return m % n === 0;
	}
}
exports.isMultipleOf = isMultipleOf;

memoize = function(f) {
	var cache = [];
	return function(n) {
		return typeof(cache[n]) === 'undefined'
				? cache[n] = f(n)
				: cache[n]
	}
}
exports.memoize = memoize;

and = function(a) {
	return function(b) {
		return null === b
				? a
				: a && b;
	}
}
exports.and = and;

tail = function(it) {
	var n = 0;
	return function() {
		var m = it();
		return n++ == 0
				? arguments.callee()
				: m
	}
}
exports.tail = tail;

isFactor = function(n) {
	return function(m) {
		return n % m == 0
	}
}
exports.isFactor = isFactor;

isPrime = function(n) {
	return (foldr
		(and)
		(null)
		(map
			(function(m) { return n % m != 0 } )
			(tail
				(tail
					(take
						(n-1)
						(nat()))))))
}
exports.isPrime = isPrime;