ComposingFunctions.cs

static class ComposingTest
{
	static private bool Not(bool x)
	{
		return !x;
	}
                                                                                        
	static private bool Even(int x)
	{
		return x % 2 == 0;
	}
                                                                                        
	static void Test()
	{
		var xs = new [] {1, 2, 3, 4};
		Func<bool, bool> not = x => !x;
		Func<int, bool> even = x => x % 2 == 0;
                                                                                        
		xs.Where(even);               // OK
		xs.Where(not.Compose(even));  // OK
                                                                                        
		xs.Where(Even);               // OK
		xs.Where(Not.Compose(Even));  // ERROR - Why?
	}
}
                                                                                        
static public class FunctionExtensions
{
	static public Func<Ta, Tc> Compose<Ta, Tb, Tc>(this Func<Tb, Tc> f, Func<Ta, Tb> g)
	{
		return x => f(g(x));
	}
}