Functional programing for Dart

ff.dart

// Functional list programinng Factory
class FF {

	static fold(func(x, r), [init, Iterable it]) =>
		init === null ?
			(init, [Iterable it]) => FF.fold(func, init, it) :
		it === null ?
			(Iterable it) => FF.fold(func, init, it) :
		(){
			var result = init;
			for (var i in it) result = func(i, result);
			return result;
		}();

	static void each(func(x), [Iterable it]){
		if (it === null) {
			return (Iterable it) => FF.each(func, it);
		}
		for (var i in it) func(i);
	}

	static Iterable map(func(v), [Iterable it]) =>
		it === null ?
			(Iterable it) => FF.map(func, it) :
		FF.fold((x, r){
			r.add(func(x));
			return r;
		}, [], it);

	static Iterable filter(bool func(v), [Iterable it]) =>
		it === null ?
			(Iterable it) => FF.filter(func, it) :
		FF.fold((x, r){
			if (func(x)) r.add(x);
			return r;
		}, [], it);

	static Iterable list(next(x), [init, bool test(x)]) =>
		init === null ?
			(init, [bool test(x)]) => FF.list(next, init, test) :
		test === null ?
			(bool test(x)) => FF.list(next, init, test) :
		(){
			var result = [];
			for (var i = init; test(i); i = next(i)) result.add(i);
			return result;
		}();

	static id(x) => x;

	static compose(Iterable<Function> fs) =>
		FF.fold((g, f) =>
			(x) => f(g(x)), FF.id, fs);
}

main(){

	String fizzbuzz(int n) =>
		n % 15 < 1 ? 'FizzBuzz' :
		n %  5 < 1 ? 'Buzz' :
		n %  3 < 1 ? 'Fizz' :
		'$n';

	int fibonacci(int n) {
		int iter(int c, [int a = 1, int b = 0]) =>
			c < 2 ? a : iter(c - 1, a + b, a);
		return iter(n);
	}

	(i, l){
		FF.each(
			FF.compose([print, fizzbuzz, fibonacci]),
			FF.list((x) => x + 1, i, (x) => x <= l));
	}(1, 1000);
}