Expression<Func<T, TRet>>に対する部分適用

test.cs

void Main()
{
	var x = 4;
	var y = 2;
	Expression<Func<int>> exp = () => x;
	Expression<Func<int, int>> twice = n => n * y;
	var param = twice.Parameters[0];
	var exp2 = new Visitor(exp.Body, twice.Body).Visit(exp);
	var exp3 = (Expression<Func<int>>)new Visitor(param, exp.Body).Visit(exp2);
	var f = exp3.Compile();
	Console.WriteLine(f());
	x = 5;
	Console.WriteLine(f());
}

// Define other methods and classes here
class Visitor : ExpressionVisitor
{
	Expression _old;
	Expression _new;
	public Visitor(Expression oldNode, Expression newNode)
	{
		_old = oldNode;
		_new = newNode;
	}
	
	public override Expression Visit(Expression node)
	{
		if (node == _old)
			return _new;
		
		return base.Visit(node);
	}
}