Mimicing Python list of list

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On Monday, 26 October 2015 at 18:46:45 UTC, Dandyvica wrote:
> Hi all,
>
> I'm trying to find out a solution to implement a generic tree 
> or array container whose nodes
> can either be elements or a subtree (or sub-array).
>
> Pretty much like you can do in Python:
>
> l = [1, 2, [1, 2, 3], 4]
>
> l is a list of (integers or list of integers).
>
> Any idea on how to do that?
>
> Thanks.

It's a bit more involved than in Python as D is not a dynamically 
typed language.

import std.typecons;
import std.stdio;

struct Tree(T)
{
	T payload;
	Tree!T[] children;
}

Tree!T tree(T)(T payload, Tree!T[] children...)
{
	return Tree!T(payload, children.dup);
}

//Convenience overload because typeof(null)
//does not implicitly convert to Tree!T[]
Tree!T tree(T)(T payload, typeof(null))
{
	return Tree!T(payload, null);
}

void printTree(T)(Tree!T tree)
{
	writeln(tree.payload);
	foreach (child; tree.children)
	{
		printTree(child);
	}
}

void main()
{
	auto intTree = tree(0,
		           tree(1,
		               tree(2)),
			   tree(3,
			       tree(4,
			           tree(5))),
			   tree(6,
			       tree(7)));

	printTree(intTree);
}

Otherwise, you an use std.variant.Variant or 
std.variant.Algebraic.