if __FILE__ == $0
  require 'test/unit'
  class TestTreeFind < Test::Unit::TestCase
    def test_flat
      assert_equal(2, treefind([1,2,3,4]) {|v| v % 3 == 2 })
      assert_equal("perl",
        treefind(["ruby", "perl", "python", "php", "lisp"]) {|v| /^p/ =~ v })
    end

    def test_string
      assert_equal(nil,
        treefind(["a\nb\n"]) {|v| v == "a\n" })
    end

    def test_nest
      assert_equal(2, treefind([[1,2],[3,[4,5]],6]) {|v| v % 3 == 2 })
    end

    def test_not_found
      assert_equal(nil, treefind([[1,2],[3,[4,5]],6]) {|v| v == 10 })
    end

    def test_nil
      assert_equal(nil, treefind([1,2,3,nil,4,5,6]) {|v| v == nil })
      assert_equal(nil, treefind([1,2,3,nil,4,5,6]) {|v| v == nil || v == 5 })
      assert_equal(nil, treefind([[1,2,3,nil,4,5,6]]) {|v| v == nil || v == 5 })
      assert_equal(nil, treefind([[nil],5]) {|v| v == nil || v == 5 })
    end

    def test_false
      assert_equal(false, treefind([1,2,3,false,4,5,6]) {|v| v == false })
      assert_equal(false, treefind([1,2,3,false,4,5,6]) {|v| v == false || v == 5 })
      assert_equal(false, treefind([[1,2,3,false,4,5,6]]) {|v| v == false || v == 5 })
      assert_equal(false, treefind([[false],5]) {|v| v == false || v == 5 })
    end

  end
end

def tree_each(obj, &b)
  if obj.respond_to? :to_ary
    obj.each {|v|
      tree_each(v, &b)
    }
  else
    yield obj
  end
end

def treefind(ary)
  tree_each(ary) {|v|
    return v if yield v
  }
  nil
end