Node dumper using y combinator

gistfile1.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

class Node {

	public string Text { get; private set; }
	public IList<Node> Children { get; private set; }

	public Node (string text, params Node [] children)
	{
		this.Text = text;
		this.Children = children ?? new Node [0];
	}
}

static class TreePrettyPrinter {

	struct NodeTuple {

		public readonly Node Node;
		public readonly bool IsTail;
		public readonly string Indent;

		NodeTuple (Node node, bool is_tail, string indent)
		{
			this.Node = node;
			this.IsTail = is_tail;
			this.Indent = indent;
		}

		public static NodeTuple Create (Node node, bool is_tail, string indent)
		{
			return new NodeTuple (node, is_tail, indent);
		}
	}

	static Func<A, R> Y<A, R> (Func<Func<A, R>, Func<A, R>> f)
	{
		Func<A, R> g = null;
		g = f (a => g (a));
		return g;
	}

	static string Print (Node node)
	{
		return Y<NodeTuple, string> (f => t =>
			t.Node.Children
				.Select (c =>
					f (NodeTuple.Create (
						c,
						c == t.Node.Children [t.Node.Children.Count - 1],
						t.Indent + (t.IsTail ? "  " : "│ "))))
				.Aggregate (
					t.Indent + (t.IsTail ? "└─" : "├─") + t.Node.Text + Environment.NewLine,
					string.Concat)
		) (NodeTuple.Create (node, true, ""));
	}

	public static void Print (TextWriter writer, Node node)
	{
		writer.WriteLine (Print (node));
	}
}

class Program {

	static void Main ()
	{
		var node = new Node ("a",
			new Node ("b",
				new Node ("c",
					new Node ("d")),
				new Node ("e",
					new Node ("f"))),
			new Node ("g",
				new Node ("h",
					new Node ("i")),
				new Node ("j"),
				new Node ("k")));

		TreePrettyPrinter.Print (Console.Out, node);
	}
}