beatz & funkz

Thursday, February 23, 2006

Building OpenLaszlo applications using Common Lisp

I have to gotten myself a small university job where I have to build a
web application using OpenLaszlo ( OpenLaszlo
is a programming language / development framework to build web
applications based on javascript and XML. Actually it is pretty
similar to all the AJAX stuff we see sprouting everywhere, except that
HTML is replaced by some kind of XML layout language. The application
is compiled to a flash swf file by the OpenLaszlo compiler, and can be
deployed in a static way (copying the swf file to a web server), or
using the OpenLaszlo middleware, which can convert HTTP calls from the
flash file to Java calls, cache resources, proxy stuff, etc… The
approach is pretty neat, the GUI is slick, quite a lot of
documentation and demo applications are available, there are no
portability problems across browsers (once you’ve got flash, but that
runs almost everywhere). Really neat, but who wants to write a
mashed-up mess of XML and Javascript?

That’s where Common Lisp comes into play. I have reworked my muddy
pile of crap ParenScript, which is some kind of Lisp to Javascript
compiler, and taken the HTML generator from Peter Seibel’s wonderful
book “Practical Common Lisp”, and glued them together to produce
human-readable OpenLaszlo XML files (called LZX files). I used my old
subversion checkout of Parenscript, and not the version maintained by
Marco Baringer, although I should do that, I guess. Let’s take a look
at such an LZX file:


This is a very simple Laszlo application, which will only show the
text “foobar”. The Lisp equivalent of this program is:

(laszlo-file "empty.lzx"
    (:text "foobar")))

LASZLO-FILE is some kind of workaround, it will interpret the body as
an XML construct and write the results to the file “empty.lzx” in my
openlaszlo development directory, where it can be accessed through the
tomcat webserver runinng the openlaszlo java program.

(:canvas (:text "foobar"))

is converted to XML using a hacked-up
version of Peter Seibel’s HTML generator. It has a few different
features. For example, node symbols are interpreted using
ParenScript’s SYMBOL-TO-JS function, so for example the following
laszlo program:

(laszlo-file "symbols.lzx"
    ((:dataset :name "foobar")
        (:my-node (:my-data "Foobar")))))

is converted to (notice the camelcase):

  <dataset name='foobar'>

The most important feature though is the integration of parenscript
into attributes which begin with “on” (for events in Laszlo), and into
the :method and :script nodes. For example:

(laszlo-file "js-example.lzx"
    (:simplelayout :axis :y :spacing 15)
    (:text :onclick (parent.toggle-text.set-visible
		     (not parent.toggle-text.visible))
	   "Click here")
    (:text :name :toggle-text :bgcolor "#CDCDCD" :visible :false "Toggle text"))))

Here the onclick attribute of the first text is a ParenScript
expression, the resulting XML is:

1: <canvas>
2:   <view>
3:     <simplelayout axis='y' spacing='15'/>
4:     <text onclick='parent.toggleText.setVisible(!parent.toggleText.visible)'>Click here</text>
5:     <text name='toggleText' bgcolor='#CDCDCD' visible='false'>Toggle text</text>
6:   </view>
8: </canvas>

The XML generator has a few special operators designed for laszlo
applications: :JS emits javascript code, :CONSTRAINT generate a laszlo
constraint expression, :JSMETHOD allows us to use a more “traditional”
style of declaring methods, and :JSEVENT a more traditional way to
declare event methods:

(laszlo-file "xml-showoff.lzx"
  (:canvas :debug :true
    (:text :width (:constraint :once parent.width) "Hello"
      (:jsevent ondata ()
         (-debug.write "Hello"))
      (:jsmethod my-method (arg1 arg2 arg3)
         (return (+ arg1 arg2 arg3))))))


1: <canvas debug='true'>
2:   <text width='$once{parent.width}'>
3:     Hello
4:     <method event='ondata' args=''>
5:       Debug.write("Hello");
6:     </method>
8:     <method name='myMethod' args='arg1,arg2,arg3'>
9:       return arg1 + arg2 + arg3;
10:     </method>
12:   </text>
13: </canvas>

ParenScript also includes a feature to generate LzDataElement XML
representations (this uses a small library fragment, which may be
expanded as needed in future times):

(laszlo-file "xml-lib.lzx"
    (defun make-simple-node (name attrs text)
      (return (new (-lz-data-element name attrs (list (new (-lz-data-text text))))))))))

(laszlo-file "xml-generation.lzx"
  (:canvas :debug :true
   (:include :href "xml-lib.lzx")
   (:text "Generate XML"
     (:jsevent onclick ()
       (xml ret (:foobar (:a :arg 1 "data")
			 (:b :arg 2 "more data")
			 (:c (:d))))
       (-debug.write (ret.serialize))))))

which generates:

1: <canvas debug='true'>
2:   <include href='xml-lib.lzx'/>
3:   <text>
4:     Generate XML
5:     <method event='onclick' args=''>
6:       var ret = new LzDataElement("foobar");
7:       ret.appendChild(makeSimpleNode("a", { arg : 1 }, "data"));
8:       ret.appendChild(makeSimpleNode("b", { arg : 2 }, "more data"));
9:       var ret0 = new LzDataElement("c");
10:       ret.appendChild(ret0);
11:       var ret1 = new LzDataElement("d");
12:       ret0.appendChild(ret1);
13:       Debug.write(ret.serialize());
14:     </method>
16:   </text>
17: </canvas>

Furthermore, the BKNR xml-impex functionality was expanded to allow
for parsing of XML update files. For example, when we have the
following class declaration:

(defparameter *root-path*
  "C:/Documents and Settings/manuel/My Documents/local-svn/laszlo/")

(defparameter *contact-dtd*
  (cxml:parse-dtd-file (merge-pathnames "contact.dtd" *root-path*)))

(defclass contact ()
  ((first-name :initarg :first-name :accessor first-name
	       :attribute "firstName")
   (last-name :initarg :last-name :accessor last-name
	      :attribute "lastName")
   (phone :initarg :phone :accessor phone
	  :attribute "phone")
   (email :initarg :email :accessor email
	  :index-type unique-index
	  :index-initargs (:test #'equal)
	  :index-reader contact-with-email
	  :index-values all-contacts
	  :attribute "email"))
  (:unique-id-slot email)
  (:unique-id-reader #'contact-with-email)
  (:metaclass xml-class)
  (:dtd *contact-dtd*)
  (:element "contact"))

(defmethod print-object ((c contact) stream)
  (print-unreadable-object (c stream :type t)
    (with-slots (first-name last-name email) c
      (format stream "\"~A ~A\" (~A)" first-name last-name email))))

(net.aserve:publish :path "/phonebook"
		    :content-type "text/xml"
		    :function #'(lambda (req ent)
				  (xml-to-http (req ent)

(make-instance 'contact
	       :first-name "Manuel"
	       :last-name "Odendahl"
	       :phone "2394802934"
	       :email "")

EXAMPLES> (all-contacts)
(#<CONTACT "Manuel Odendahl" (>)

EXAMPLES> (write-to-xml (all-contacts) :name "contacts")
   <contact email="" firstName="Manuel" lastName="Odendahl" phone="2394802934"/>

We can parse the following “update.xml” file:

<updates><contact email=''lastName='foobar'/></updates>

EXAMPLES> (parse-xml-update-file "update.xml" (list (find-class 'contact)))
updating slot LAST-NAME with "foobar"
(:CONTACT (#lt;CONTACT "Manuel foobar" (>)

This can be further wrapped into a web service:

(net.aserve:publish :path "/phonebook"
		    :content-type "text/xml"
		    :function #'(lambda (req ent)
				  (xml-to-http (req ent)
					       (all-contacts) :name "phonebook")))

(defun phonebook-update (req)
  (with-query-params (req action xml pk)
    (warn "action ~A, xml ~A" action xml)
      ((string= action "insert")
       (insert-xml-class 'contact xml :parse #'bknr.impex:parse-xml-stream))
      ((string= action "update")
       (update-xml-class 'contact xml :parse #'bknr.impex:parse-xml-update-stream))
      ((string= action "delete")
       (destroy-object (contact-with-email pk))))))

(net.aserve:publish :path "/phonebook-update"
		    :content-type "text/xml"
		    :function #'(lambda (req ent)
				  (handler-case (phonebook-update req)
				    (error (e)
				      (warn "error: ~A" e)
				      (xml-http-output (req ent)
						       (:result "failure")))
				    (:no-error (e)
				      (declare (ignore e))
				      (xml-http-output (req ent)
						       (:result "success"))))))

(net.aserve:start :port 8081)

Which allows to rebuild the example data application out of the laszlo
developer manual using Lisp:

(laszlo-file "data-app8.lzx"
  ((:canvas :bgcolor "#D4D0C8" :debug "true")
   (:include :href "xml-lib.lzx")
   (:dataset :name "dset" :src "http://localhost:8081/phonebook" :request "true" :type "http")

   ((:dataset :name "dsSendData" :request "false" :src "http://localhost:8081/phonebook-update"
	      :type "http"))

   ((:datapointer :xpath "dsSendData:/")
    ((:method :event "ondata")
     (if (= (this.xpath-query "result/text()") "success")
	 (-Debug.write "Operation succeeded")
	 (-Debug.write "Operation failed"))))

   ((:class :name "contactview" :extends "view" :visible "false" :x 20 :height 120)
    (:text :name "pk" :visible "false" :datapath "@email")
    (:text :y 10 "First Name:")
    (:edittext :name "firstName" :datapath "@firstName" :x 80 :y 10)
    (:text :y 35 "Last Name:")
    (:edittext :name "lastName" :datapath "@lastName" :x 80 :y 35)
    (:text :y 60 "Phone:")
    (:edittext :name "phone" :datapath "@phone" :x 80 :y 60)
    (:text :y 85 "Email:")
    (:edittext :name "email" :datapath "@email" :x 80 :y 85)

    ((:method :name "sendData" :args "action")
     (let ((d canvas.datasets.ds-send-data)
	   (p (new -lz-param)))
       (xml xmlret (:update (:contact :first-name (first-name.get-text)
				      :last-name (last-name.get-text)
				      :phone (phone.get-text)
				      :email (email.get-text))))
       (p.add-value "action" action t)
       (p.add-value "xml" (xmlret.serialize) t)
       (p.add-value "pk" (pk.get-text) t)
       (d.set-query-string p)

   (:simplelayout :axis "y")

    (:simplelayout :axis "y")
    (:text :onclick ( (not
	   "New Entry...")

    ((:contactview :name "newContact" :datapath "new:/contact")
     ((:button :width 80 :x 200 :y 10) "Add"
      ((:method :event "onclick")
       (parent.send-data "insert")
       (let ((dp (canvas.datasets.dset.get-pointer)))
	 (dp.add-node-from-pointer parent.datapath)
	 (parent.set-visible false)
	 (parent.set-datapath "new:/contact")))))
    ((:view :datapath "dset:/phonebook/contact")
     (:simplelayout :axis "y")
     ((:view :name "list" :onclick (parent.update-contact.set-visible
				    (not parent.update-contact.visible)))
      (:simplelayout :axis "x")
      (:text :datapath "@firstName")
      (:text :datapath "@lastName")
      (:text :datapath "@phone")
      (:text :datapath "@email"))

     ((:contactview :name "updateContact")
      ((:button :width 80 :x 200 :y 10) "Update"
       ((:method :event "onclick")
	(parent.send-data "update")

      ((:button :width 80 :x 200 :y 40) "Delete"
       ((:method :event "onclick")
	(parent.send-data "delete")
    (:debug :width 600 :height 120)))

Now this is still much to write, and there is no persistence on the
server side. The persistence is handled by the BKNR datastore, and a
few wrappers enable us to pack everything into a few lines:

(defvar *user-dtd*
  (cxml:parse-dtd-file "user.dtd"))

(define-persistent-class user (xml-store-object)
  ((first-name :update :element "firstName")
   (last-name :update :element "lastName")
   (vat-number :update :element "vatNumber")
   (email :update :index-type string-unique-index
	  :index-reader user-with-email
	  :index-values all-users
	  :element "email"))
  (:metaclass persistent-xml-class)
  (:dtd *user-dtd*)
  (:element "user"))

(defmethod print-object ((user user) stream)
  (print-unreadable-object (user stream :type t)
    (with-slots (first-name last-name email) user
      (format stream "~a ~a (~a)" first-name last-name email))))

(make-instance 'mp-store :directory "C:/Documents and Settings/manuel/My Documents/laszlo-store/"
	       :subsystems (list (make-instance 'store-object-subsystem)))

(make-object 'user
	     :first-name "Manuel"
	     :last-name "Odendahl"
	     :vat-number "23849"
	     :email "")

(publish-xml-handler 'user)

(laszlo-file "userdemo.lzx"
  ((:canvas :height 400 :debug "true")

   (:include :href "xml-lib.lzx")

   (:dataset :name "user" :src "" :type "http" :autorequest "true")

   ((:dataset :name "updateDs" :src "" :type "http"
	      :request "false" :autorequest "false"))

   ;;; wieso wird der scheiss nicht dann aufgerufen, wenn er aufgerufen werden soll? XXX
   ((:datapointer :xpath "updateDs:/")
    ((:method :event "ondata")
     (-debug.write (+ "on-data" (.serialize (this.get-dataset))))
     (-debug.write (this.xpath-query "/result[1]/text()"))
     (if (= (this.xpath-query "/result[1]/text()") "success")
	 (-debug.write "update was successful")
	 (-debug.write "update was not successful"))))
   (:datapointer :id "userdp" :xpath "user:/user[1]")

   (:simplelayout :axis "y")

   (:jsmethod edit-user ()
     (if this.edit-data.visible
     ( (not
     (this.edit-data.set-visible (not this.edit-data.visible)))

   ((:view :name "showData" :datapath "user:/user[1]" :visible "true")
    (:text :x 0 :y 0 "First Name:")
    (:text :x 150 :y 0 :name "firstName" :datapath "firstName/text()")
    (:text :x 0 :y 25 "Last Name:")
    (:text :x 150 :y 25 :name "lastName" :datapath "lastName/text()")
    (:text :x 0 :y 50 "VAT Number:")
    (:text :x 150 :y 50 :name "vatNumber" :datapath "vatNumber/text()")
    (:button :y 100 :onclick (parent.parent.edit-user) "Edit Data"))
   ((:view :name "editData" :visible "false")
    (:jsmethod set-data ()
       (this.first-name.set-text (userdp.xpath-query "/user[1]/firstName/text()"))
       (this.last-name.set-text  (userdp.xpath-query "/user[1]/lastName/text()"))
       (this.vat-number.set-text (userdp.xpath-query "/user[1]/vatNumber/text()")))

    (:jsmethod update-data ()
       (xml update (:update ((:user :id (userdp.xpath-query "/user[1]/@id"))
			     (:first-name (this.first-name.get-text))
			     (:last-name  (this.last-name.get-text))
			     (:vat-number (this.vat-number.get-text)))))
       (let ((p (new -lz-param)))
	 (p.add-value "action" "update" t)
	 (p.add-value "update" (update.serialize) t)
	 (update-ds.set-query-string p)
	 (-debug.write "")
    (:text :x 0 :y 0 "First Name:")
    (:edittext :x 150 :y 0 :name "firstName")
    (:text :x 0 :y 25 "Last Name:")
    (:edittext :x 150 :y 25 :name "lastName")
    (:text :x 0 :y 50 "VAT Number:")
    (:edittext :x 150 :y 50 :name "vatNumber")

    (:button :y 100 :onclick (parent.update-data) "Update Data"))

   ((:button :onclick (progn (parent.form.datapath.update-data)
			     (t.set-text (userprofile.serialize)))) "Show XML data")
   (:inputtext :multiline "true"
	       :width (:constraint nil canvas.width)
	       :bgcolor "0xa0a0a0"
	       :id "t"
	       :height 300)

Now all this code is extremely brittle (it has been about a year since
my last programming), quickly hacked together and by no means
finished. I won’t even suggest you to get it to work, and I only
include a dump of my local-svn containing the XML and ParenScript for
sakes of completeness (the IMPEX and persistence stuff is not ready
for release)

posted by manuel at 7:21 pm  


  1. P. Tucker Withington of is a former super Lisp hacker who now works for Laszlo Systems. His blog usually has interesting stuff about OpenLaszlo.

    Comment by Zach Beane — February 23, 2006 @ 9:28 pm

  2. Sweet!

    I got here via a web search for lisp xml generation. I’m doing a lot of generating of XML for various XML-based languages, which seems like a perfect match for Lisp, but there isn’t much in the way of XML *generation* libraries for Lisp.

    This is almost exactly what I’m looking for. Thanks!

    The one thing that’s not clear to me is: this works great if you have a template you want to fill in with various values, but what if you want the structure of your XML to be determined at runtime? It’s easy to say (:text …) 4 times for 4 text boxes, but what if I want /n/ boxes, based on my data? It looks like I’d need another macro to generate *that* (with ,@…), and that makes my head start to hurt again, which makes me think it’s not really the best approach. Hmm.

    Anyway, keep up the good work!

    Comment by Ken — May 18, 2006 @ 5:32 pm

  3. This is great! I too am building a web application using OpenLaszlo and Lisp; unlike yourself, I haven’t done anything similar before, so I look forward to learning a lot from your code. Thanks very much for making it available.

    Cheers, John :^P (Wellington, New Zealand)

    Comment by John Pallister — October 16, 2006 @ 6:25 am

  4. thank you! thank you! thank you!!!!

    Comment by Gabriel — December 16, 2006 @ 9:31 pm

  5. Your zip file

    seems to be broken. I cannot unzip it.
    Could you check it ?


    Comment by Hot Michel — February 8, 2007 @ 2:09 pm

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