edpth-first search Elixir

dfs.ex

@doc """
	Does a Depth-First Search in the given 'tree'. The nodes' values are
	returned in a list. The order of the search is passed into 'order' using
	the atoms ':in_order', ':pre_order' or ':post_order'
	"""
	@spec depth_first_search(%{}, atom) :: list(any)

	def depth_first_search(tree, order) when order == :pre_order or 
																					 order == :in_order  or 
														 							 order == :post_order do 
		dfs tree, order
	end

	defp dfs(:leaf, _), do: []
	defp dfs(%{value: val, left: :leaf, right: :leaf}, _), do: [val]
	defp dfs(tree_node, order) do
		case order do
		  :pre_order 	->
			  [tree_node.value]   			 ++ dfs(tree_node.left, order)  ++ dfs(tree_node.right, order)
			:in_order   ->
				dfs(tree_node.left, order) ++ [tree_node.value]   				++ dfs(tree_node.right, order)
			:post_order ->
				dfs(tree_node.left, order) ++ dfs(tree_node.right, order) ++ [tree_node.value]
		end

	end