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module TSort[Node]
  interface _Sortable[Node]
    # #tsort_each_node is used to iterate for all nodes over a graph.
    #
    def tsort_each_node: () { (Node) -> void } -> void

    # #tsort_each_child is used to iterate for child nodes of node.
    #
    def tsort_each_child: (Node) { (Node) -> void } -> void
  end

  interface _EachNode[Node]
    def call: () { (Node) -> void } -> void
  end

  interface _EachChild[Node]
    def call: (Node) { (Node) -> void } -> void
  end
end