// Linq.cs

using System.Collections;
using Microsoft.SPOT;

namespace System.Runtime.CompilerServices {
	[AttributeUsageAttribute(
		AttributeTargets.Assembly
		| AttributeTargets.Class
		| AttributeTargets.Method)]
	sealed class ExtensionAttribute: Attribute {}
}

delegate bool Predicate (object o);

sealed class Enumerator: IEnumerator {
	IEnumerator e;
	Predicate p;

	internal Enumerator (IEnumerator e, Predicate p) {
		this.e = e;
		this.p = p;
	}

	object IEnumerator.Current {
		get { return e.Current; }
	}

	void IEnumerator.Reset () {
		e.Reset();
	}

	bool IEnumerator.MoveNext () {
		var b = e.MoveNext();
		while (b && !p(e.Current)) {
			b = e.MoveNext();
		}
		return b;
	}
}

sealed class Filter: IEnumerable {
	IEnumerable e;
	Predicate p;

	internal Filter (IEnumerable e, Predicate p) {
		this.e = e;
		this.p = p;
	}

	IEnumerator IEnumerable.GetEnumerator () {
		return new Enumerator(e.GetEnumerator(), p);
	}
}

static class Program {
	static int Count (this IEnumerable e) {
		var n = 0;
		foreach (var o in e) {
			n++;
		}
		return n;
	}

	static IEnumerable Where (this IEnumerable e, Predicate p) {
		return new Filter(e, p);
	}

	static void Main () {
		var a = new int[] {1, 2, 3, 4, 6, 8, 9, 9, 9};
		var n = a.Where(v => (int) v % 2 == 0).Count();
		var m = (from v in a where (int) v % 2 == 0 select v).Count();
		Debug.Print(n + " " + m);
	}
}