rosa/inc/tmp/tree.h

#ifndef TMP_TREE_H
#define TMP_TREE_H

#include "bind.h"
#include "pack.h"
#include "packalgo.h"
#include "utility.h"

namespace tmp {

/**
 * Tree
 */
template<typename...> struct Tree;

template<typename N, typename... Cs>
struct Tree<N, Cs...> {
	using node      = N;
	using children  = Pack<Cs...>;
};

template<>
struct Tree<> {};

/**
 * TreeNode
 *
 * for use in flat tree representations
 */
enum class TreeNodeType { Branch, Leaf };
template<Depth D, typename T, TreeNodeType N>
struct TreeNode {
	static constexpr Depth depth            = D;
	using type                              = T;
	static constexpr TreeNodeType nodeType  = N;
};

template<typename T, TreeNodeType NT = TreeNodeType::Branch>
using TreeRoot = TreeNode<0, T, NT>;

template<Depth D, typename T>
using TreeBranch = TreeNode<D, T, TreeNodeType::Branch>;

template<Depth D, typename T>
using TreeLeaf = TreeNode<D, T, TreeNodeType::Leaf>;

/**
 * TreeIsLeaf
 */
template<typename> struct TreeIsLeafImpl: std::true_type {};
template<typename... Ts>
struct TreeIsLeafImpl<Tree<Ts...>>: std::false_type {};

template<typename T>
constexpr bool TreeIsLeaf = TreeIsLeafImpl<T>::value;

/**
 * PackFromTreeNLR
 *
 * creates a pack from a tree using NLR
 * tree traversal algorithm
 */
template<typename, Depth=0> struct PackFromTreeNLRImpl;

template<typename N, typename... LRs, Depth D>
struct PackFromTreeNLRImpl<Tree<N, LRs...>, D> {
	using type = PackPushFront<
		PackCat<typename PackFromTreeNLRImpl<LRs, D+1>::type...>,
		TreeBranch<D, N>
			>;
};

template<typename N, Depth D>
struct PackFromTreeNLRImpl<Tree<N>, D> {
	using type = Pack<TreeLeaf<D, N>>;
};

template<Depth D>
struct PackFromTreeNLRImpl<Tree<>, D> {
	using type = Pack<>;
};

template<typename T, Depth D = 0>
using PackFromTreeNLR = typename PackFromTreeNLRImpl<T, D>::type;

/**
 * TreeFromPackNLR
 *
 * creates a tree from a pack
 * reverses PackFromTreeNLR
 */
namespace detail {

template<Depth D, typename T>
using PartialTree = Pack<std::integral_constant<decltype(D), D>, T>;

template<Depth LIM>
struct GreaterThan {
	template<typename T, typename=void> struct CmpImpl;
	template<Depth D, typename T>
	struct CmpImpl<PartialTree<D, T>>: std::integral_constant<bool, (D > LIM)> {};
	template<typename T>
	struct CmpImpl<T>: std::true_type {};

	template<typename T>
	using Cmp = CmpImpl<T>;
};

}

/* property:
 * one block either groups future blocks or
 * has a bigger or equal depth than following
 *
 * property:
 * the list of depths when building is always
 * decreasing (quite easy to demonstrate)
 */
template<typename, typename=void> struct TreeFromPackNLRImpl;

template<Depth D, typename T, typename... Ns>
struct TreeFromPackNLRImpl<Pack<TreeBranch<D, T>, Ns...>, std::enable_if_t<D != 0>> {
	using next      = typename TreeFromPackNLRImpl<Pack<Ns...>>::subtree;
	using cutd      = Cut<next, detail::GreaterThan<D>::template Cmp>;
	using children  = Transform<PackGet<cutd, 0>, Bind2ndV<Size, PackGet, 1>::template F1>;
	using siblings  = PackGet<cutd, 1>;
	using part      = detail::PartialTree<D, Repack<Tree, PackPushFront<children, T>>>;
	using subtree   = PackPushFront<siblings, part>;

	using type      = Repack<Tree, subtree>;
};

template<typename T, TreeNodeType NT, typename... Ns>
struct TreeFromPackNLRImpl<Pack<TreeRoot<T, NT>, Ns...>> {
	using next      = typename TreeFromPackNLRImpl<Pack<Ns...>>::subtree;
	using children  = Transform<next, Bind2ndV<Size, PackGet, 1>::template F1>;
	using subtree   = PackPushFront<children, T>;
	using type      = Repack<Tree, subtree>;
};

template<Depth D, typename T, typename... Ns>
struct TreeFromPackNLRImpl<Pack<TreeLeaf<D, T>, Ns...>, std::enable_if_t<D != 0>> {
	using part    = detail::PartialTree<D, Tree<T>>;
	using subtree = PackPushFront<typename TreeFromPackNLRImpl<Pack<Ns...>>::subtree, part>;
	using type    = Repack<Tree, subtree>;
};

template<>
struct TreeFromPackNLRImpl<Pack<>> {
	using subtree = Pack<>;
	using type    = Repack<Tree, subtree>;
};

template<typename P>
using TreeFromPackNLR = typename TreeFromPackNLRImpl<P>::type;

}

#endif