Often, programs have to generate XML output. This is fairly easy, but not quite trivial. You need to do escaping, and indentation can be a little tricky to keep track of. One approach you could use is to get an XML parser/unparser like XMLS, build your XML data structure in memory, then dump the whole thing. This is fairly easy, but not as easy as it could be, and it requires holding the whole structure in memory.

So, I wrote xml-emitter. xml-emitter simply emits XML, with some complexity for handling indentation. It can be used to produce all sorts of useful XML output; it has an RSS 2.0 emitter built in, so you can make RSS feeds trivially.

There is no real home page, but you can download it from the asdf-packaging project. Or from the download link on this page.

If you have comments, questions, or bug reports, email them to Peter Scott .

Update (August 2015):

  • Now there is an official repository: xml-emitter maintained by Vito Van, feel free to submit issues and pull requests.


The WITH-XML-OUTPUT macro wraps all XML output to a stream.

The WITH-TAG macro places the XML produced by its body inside a tag. Its output cannot be on just one line, since it puts starting and closing tags on their own lines.

The WITH-SIMPLE-TAG macro is like WITH-TAG, but starting and closing tags don't get their own lines.

XML-OUT prints its argument to the XML output stream, escaped.

XML-AS-IS prints its argument to the XML output stream, unescaped.

SIMPLE-TAG prints a simple <tag>value</tag> tag. It's a shortened version of a typical use of WITH-SIMPLE-TAG and XML-OUT.

EMIT-SIMPLE-TAGS takes a plist of tag names and tag values. For every tag with a non-NIL value, it prints the tag with SIMPLE-TAG. Tag names given as keyword symbols (like :this) are downcased.


(with-xml-output (*standard-output*)
  (with-tag ("person" '(("age" "19")))
    (with-simple-tag ("firstName")
      (xml-out "Peter"))
    (simple-tag "lastName" "Scott")
    (emit-simple-tags :age 17
		      :school "Iowa State Univeristy"
		      "mixedCaseTag" "Check out the mixed case!"
		      "notShown" nil)))

The RSS 2.0 emitter

The WITH-RSS2 macro wraps up all output of RSS.

RSS-CHANNEL-HEADER outputs the RSS channel information.

RSS-ITEM outputs information about one RSS item.


(with-rss2 (*standard-output*)
  (rss-channel-header "Peter's Blog" "http://peter.blogspot.com/"
		      :description "A place where I sometimes post stuff"
		      :image "myhead.jpg"
		      :image-title "My glorious visage")
  (rss-item "Breaking news!"
	    :link "http://google.com/"
	    :description "The biggest problem with the DO-ODD macro above is that it puts BODY
into LOOP. Code from the user of the macro should never be run in the
environment established by the LOOP macro. LOOP does a number of
things behind your back, and it's hard to disable them. For example,
what happens here?"
	    :author "Peter Scott"
	    :category "Lisp"
	    :pubDate "Sun, 29 Sep 2002 19:59:01 GMT")
  (rss-item "RSS emitter created"
	    :description "An RSS emitter has been released! Hahahahaha!"
	    :author "Peter Scott"
	    :link "http://gmail.google.com/"))

There is also a complete example of how you might use the RSS emitter in mailbox.lisp in the source distribution.