List.d

class List(T) {
	public T head;
	public List!(T) tail;

	public this(T val) {
		this.head = val;
		this.tail = null;
	}
	public this(T[] arr) {
		if(arr.length - 1 == 0){
			this.head = arr[0];
			this.tail = null;
		} else {
			this.head = arr[0];
			this.tail = new List!T(arr[1 .. $]);
		}
	}
	private this(T val, List!T list) {
		this.head = val;
		this.tail = list;
	}
	private this(List!T list) {
		this.head = list.head;
		if(list.tail)
			this.tail = new List!T(list.tail);
	}

	private List!T junction(List!T list) {
		if(this.tail) {
			return this.tail.junction(this, list);
		} else {
			this.tail = list;
			return this;
		}
	}
	private List!T junction(List!T ret, List!T list) {
		if(this.tail) {
			return this.tail.junction(ret, list);
		} else {
			this.tail = list;
			return ret;
		}
	}

	public List!T dup() {
		return new List!T(this);
	}

	public static List!T cons(T val, List!T list) {
		return new List!T(val, list);
	}
	public static List!T cons(T val1, T val2) {
		return new List!T([val1, val2]);
	}
	public static List!T cons(List!T list1, List!T list2) {
		return list1.dup.junction(list2);
	}


	public void for_each(void delegate(T) del) {
		del(this.head);
		if(this.tail !is null)
			this.tail.for_each(del);
	}
	public void for_each(void function(T) func) {
		func(this.head);
		if(this.tail !is null)
			this.tail.for_each(func);
	}

	public T foldl(T accum, T delegate(T, T) del) {
		return this.tail?
			(this.tail.foldl(del(accum, this.head), del))
			: del(accum, this.head);
	}
}