alt.swift

       let bookTuples = [(1, "john", "book", "novel", 9.99, ["chapt1", "chapt2"]),
                         (2, "john", "book", "novel", 9.99, ["chapt1", "chapt2"])]

      // leaves blank line when there are no values in the list
        let json1 = """
            {
                "catalog": [
            \(bookTuples.map {
            (id, author, title, genre, price, chapters) in """
                    {
                        "id": "id\(id)",
                        "author": "\(author)",
                        "title": "\(title)",
                        "genre": "\(genre)",
                        "price": \(price),
                        "chapters": [
            \(chapters.map {
                            (heading) in """
                            "\(heading)"
            """}.joined(separator:",\n"))
                        ]
                    }
            """}.joined(separator:",\n"))
                ]
            }
            """

        // no blank line but extra comma at the end
        let json2 = """
            {
                "catalog": [
            \(bookTuples.map {
            (id, author, title, genre, price, chapters) in """
                    {
                        "id": "id\(id)",
                        "author": "\(author)",
                        "title": "\(title)",
                        "genre": "\(genre)",
                        "price": \(price),
                        "chapters": [
            \(chapters.map {
                            (heading) in """
                            "\(heading)",

            """}.joined(separator:"")
            )           ]
                    },

            """}.joined(separator:"")
            )    ]
            }
            """
  
      print("""
            <?xml version="1.0"?>
            <catalog>
            \(bookTuples.map {
                (id, author, title, genre, price, chapters) in """
                <book id="bk\(id)" empty="">
                    <author>\(author)</author>
                    <title>\(title)</title>
                    <genre>\(genre)</genre>
                    <price>\(price)</price>
                    <chapters>
            \(chapters.map {
                        (heading) in """
                        <heading>\(heading)</heading>

            """}.joined(separator:"")
            )        </chapters>
                </book>

            """}.joined(separator:"")
            )</catalog>
            """)
                  
      // elided newlines with no trailing newline stripping
      print("""
            <?xml version="1.0"?>
            <catalog>
            \(bookTuples.map {
                (id, author, title, genre, price, chapters) in """
                <book id="bk\(id)" empty="">
                    <author>\(author)</author>
                    <title>\(title)</title>
                    <genre>\(genre)</genre>
                    <price>\(price)</price>
                    <chapters>
            \(chapters.map {
                        (heading) in """
                        <heading>\(heading)</heading>
            """}.joined(separator:""))\
                    </chapters>
                </book>
            """}.joined(separator:""))\
            </catalog>
            """)