Using Xml to Create XML and XHTML

Category: Coding

Problem

You need to create HTML (or XML or XHTML) strings.

Ingredients

Xml function, string concatenation, blocks, QueryAccum

Recipe

The Xml function in stdlib provides a simple yet flexible way to generate XML.

The simplest form is a tag with no content:

Xml("br")

    => "<br />"

The next step up is wrapping a string with tags:

Xml("em", "hello")

    => "<em>hello</em>"

You can also add attributes:

Xml("td", "hello world", valign: "top", bgcolor: "red")

    => '<td valign="top" bgcolor="red">hello world</td>'

Attributes can be used for inline CSS styles:

Xml("span", "hello world", style: "color: red; font-size: 20pt;")

    => '<span style="color: red; font-size: 20pt">hello world</span>'

Calls to Xml can of course be nested and concatenated:

Xml("table",
    Xml("tr", Xml("td", "top left") $ Xml("td", "top right")) $ "\n" $
    Xml("tr", Xml("td", "bottom left") $ Xml("td", "bottom right")),
    border: 1)

    => '<table border="1"><tr><td>top left</td><td>top right</td></tr>
       <tr><td>bottom left</td><td>bottom right</td></tr></table>'

Notice that the attributes must follow the content. This is because in Suneido function calls un-named arguments (i.e. the content) must come before named arguments.

Xml will also accept a block as the content. This allows you, for example, to wrap tag(s) around content produced by a loop.

Xml("table")
    {
    Xml('tr', Xml('td', "Table") $ Xml('td', "Size")) $ "\n" $
    QueryAccum("tables", "")
        { |s, x|
        s $ Xml('tr', Xml('td', x.tablename) $ Xml('td', x.totalsize)) $ "\n"
        }
    }

Notice the addition of newlines in the last two examples. Although this is not strictly necessary, it makes the resulting XML much more human readable.

Discussion

Using Xml instead of straight string manipulation has a number of advantages:

• you don't have to type so many angle brackets!
• it automatically generates matching end tags, avoiding missing or mismatched tags
• empty elements (with no content) automatically generate the closing slash required by XML and XHTML (e.g. <br />
• all attribute values are quoted as required by XML and XHTML
• the code is more readable

See Also

Building a Large String a Piece at a Time