From: “Will Hartung” Newsgroups: comp.lang.lisp Subject: Guerilla Lisp – The OPUS (was Re: some stuff about the 2002 International Lisp Conference in SF) Lines: 347 X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2600.0000 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 Message-ID: <4caA9.1572$> NNTP-Posting-Host: X-Complaints-To: ab… NNTP-Posting-Date: Tue, 12 Nov 2002 11:42:40 EST Organization: Prodigy Internet Date: Tue, 12 Nov 2002 16:42:40 GMT Xref: comp.lang.lisp:46391

“Coby Beck” wrote in message news:aqphij$du8$…

You used lisp to do it? It’s relevant! Send that opus over… :)

I got several requests for this thing, so I figured I’d post it rather than send out several copies.

—– Original Message —– From: “Brian Palmer” brian@invalid.dom Newsgroups: comp.lang.lisp Sent: Monday, November 11, 2002 2:52 AM Subject: Re: some stuff about the 2002 International Lisp Conference in SF

Will Hartung wrote:

Lisp is a tool as much as Javascript is a tool. I used it in a Microsoft shop writing J2EE Java code for Suns to create Java code. … And ya know what? The client had NO IDEA how I was doing “my magic”. Lisp was my tool, yet Java was their solution.

I’d love to hear more about how this is done, either your case in particular or a pointer to some articles/books which describe something like this. I’m intrigued!

Our application is a J2EE “Care Management System”. The basic premise is that an organization such as a Medical Group would enroll patients into particular programs to help track their status. Example programs are Cardio Vascular Disease and Diabetes. I think I’m not alone here on working on such a project.

The Care Manager would engage the patient with pre-planned questionnaires that ask about the patients current conditions, habits, history, etc.

Then, while the patient is within the program either the patient would log in directly, or the Care Manager would contact them with followup questions and status. So, over time, the data entered into the system would help with things like tracking a persons weight, or blood pressure or even medication interactions.

The key to the system was a set of “Rule logic” that checks the data and creates the next step in the workflow for the patient. For example, the system could see that a patients weight is going up over a short period, and that may be a trigger to alert their physician. Things like that.

All of those rules are considered “clinical content”, and they’re written by, of all things, Clinicians. Clinician are the medical knowledge for the project, but they are NOT “computer people”.

I had written a scripting language which made it easier to create these rules, because it made access to the data model much easier and abstracted the higher end results of the rules (tasks, messages, etc). All of the clinical content is supposed to be written in this scripting language called RSL. It’s your basic ALGOLesqe scripting language, with simple IF-THEN statements. Ideally, all of this would be done as some kind of simple expert system, but what was originally specified and what we have today are different beasts, so we work with the tools we have.

RSL is organized into execution blocks called Packages, and these were associated to the questionnaires. While there are, essentially, subroutines and functions in RSL, the real level of abstraction was the Package, with a list of variables needed from the database enumerated at the top the file, in a pacakge-wide namespace, and then followed by the logic.

The clinical content was defined by the clinicians in spreadsheets. They would specify the variable they were populating, and how it was calculated. Later they would specify messages based on variable results.

A very simple example: HEIGHT_FEET – Height in Feet (prompted variable) HEIGHT_INCHES – Height in Inches (prompted variable) [ For “What’s your height in feet and inches”] WEIGHT_LBS – Weight in pounds (prompted variable) TOTAL_HEIGHT = HEIGHT_FEET * 12 + HEIGHT_INCHES WEIGHT_KILOS = WEIGHT_LBS / 0.6 BMI = WEIGHT_KILOS / TOTAL_HEIGHT

BMI is the “Body Mass Index”, and this isn’t the actual calculation, just an example. But basically the BMI lets us easily determine if someone is too heavy or or not for their size. So, if you were 4ft 2in and weighed 300lbs, you’re “too heavy”.

So, given these variables, they would create a rule. (These ratings are complete BS, I just made them up.)

BMI > 4 – Message “You’re too heavy” BMI > 3 – Message “You’re just right” OTHERWISE – Message “You’re too light”

Now, when given this rule, the BMI variable would actually be defined in a completely different spreadsheet. If I were to code this in RSL, I’d write something like this:

PACKAGE TEST VAR HEIGHT_FEET = HEIGHT_FEET // This is how we access vars in the DB VAR HEIGHT_INCHES = HEIGHT_INCHES // The name after the = identifies the variable VAR WEIGHT_LBS = WEIGHT_LBS WORKVAR TOTAL_HEIGHT = NUMBER // Workvars are local variable, and note that they’re typed. WORKVAR WEIGHT_KILOS = NUMBER WORKVAR BMI = NUMBER


IF BMI > 4 THEN MESSAGE “You’re too heavy” ELSEIF BMI > 3 THEN MESSAGE “You’re just right” ELSE MESSAGE “You’re too light” ENDIF

Pretty straight forward.

But as an RSL Coder, I had to look up BMI, find out that it used TOTAL_HEIGHT and WEIGHT_KILOS. Then I had to look THOSE up, and find out how they were defined. Finally, I had to ensure that they were in the proper order, etc.

The issue was, of course, that there were hundreds of rules and variables, not simply these few. The other issue was that these were being developed while they were being coded, and the changes were all very local.

If they changed the definition of BMI, I’d have to go through the code, find BMI, find out what variables it was using, and if I was thorough, I’d check to see if the old variables weren’t being referenced any more and delete them. The key being that all of these rules and variables were very interdependent, so any changes had the potential to ripple through all of the code. Plus, they were not quite sure which rules (like the BMI rule) were to fire for which questionnaires. So, if they decided that Questionnaire A no longer needed the BMI rule, they would take it out. But since the code was basically designed to handle the individual questionnaires, then I’d have to change that code as well. Or worse, if BMI was used in several questionnaires, I’d have to change all of the files that they were referenced in, and ensure that they’re all using the new logic. It was a real pain.

Now, I saw this issue immediately, and I thought it was terrible.

While I had written the RSL compiler, which converts the RSL into Java, (I didn’t design the language), I had never actually USED RSL for clinical content. I had never seen the actual clinical content the “Scripters” were supposed to be creating RSL from. The original goal was that RSL would be easy enough for the Clinicians to do it themselves. That, obviously, did not happen.

So, this was my first exposure to real, authentic Clinical Content, and these relationships between the variables, and their rules was glaring.

So, what I did was I started to code up the spreadsheets I had as simple structures.

(DEFVAR WEIGHT_LBS type NUMBER desc “Weight in Lbs” class DBVAR) (DEFVAR WEIGHT_KILOS type NUMBER desc “Weight in kilos” class WORK INIT (set WEIGHT_KILOS (/ WEIGHT_LBS 0.6))) (DEFVAR BMI type NUMBER desc “BMI” class WORK INIT (set BMI (/ WEIGHT_KILOS TOTAL_HEIGHT)))

(MESSAGE BMI-1 (WHEN (> BMI 4) (MESSAGE “You’re too heavy”)) (WHEN (> BMI 3) (MESSAGE “You’re just right”)) (OTHERWISE (MESSAGE “You’re too light”)))

I simply just typed everything in like this, just filling in the stuff I knew into a Lispy syntax, not even sure what I was going to do with it. But I was confident that I could always quickly generate something if the project dragged because of this and drop back into “pure RSL”.

After I coded the Variables and rules into these structures, I started writing code to manipulate them. To pick out the dependencies and keep track.

The beauty of this was that my Lispy stuff was almost one to one with the specs, save for being in prefix vs infix. It was also very clear very quickly that this was going to be a great time saver. The dependencies were “self declaring”, just by using a variable in an expression. If I were to get a change in a calculation, I could simply go to the variable definition and change it, without worrying about the change bubbling through the code.

The goal started to simply capture all of the info I had available (a simple spreadsheet), and capture it into a form that was easily manipulated by the computer. When changes came, I captured those also.

Since there was so much commonality to the rules and their structure, basic problems with the system were solved just once.

So, in the end I simply wrote a basic “RSL Compiler” to convert these structures. I was able to define the relationships between the packages and the rules they contained, as well as the packages and questionnaires that fed them. And it was all done with little thought. Little up front planning. Like I said in the beginning I did not know what I was really going to do with the information when I started, but I knew that a) changes were coming, and that b) it was going to be a lot easier to work with the “code as data” concept than just straight code.

Once I had large chunks of the rules and variables coded, the solution started to present itself. By using the implicit declarations of the the variables within other variables and rules, it was simple to organize the data and build dependencies to generate the code correctly. In this case, I would simply say that a Package contained the BMI-1 message rule, and the compiler drags in all of its dependents, structured and ordered the declarations properly, and generated the correct code. If the package contained BMI-1 and BMI-2, then the common variables would only be used once, everything would be simply organized. No real rocket science here.

With the compiler doing all of the work, the client was able to send quick changes over through email after short dicussions via AIM. Once I got the change, it was usually simple to implement because the monsterous side effects were all handled automatically. Adding or removing a variable from a rule could eventually add a dozen or more dependent variables into the final code, but the change was simply adding the variable to the rule.

When systems have a lot of code, they tend to gain a momentum of their own and become resistant to change. This system had almost no momentum, regardless of the number of rules. This lack of momentum also made testing simpler because as long as the actual information from the original spreadsheets were captured accurately, the rest of the system would, mostly, just work. If it didn’t work, it was a clinical issue, but not a technical one.

Late in the project, they completely changed some major pieces of the specification. Had this been done the original way, I would have had to go to each rule implementation, beat it into submission, make sure I didn’t get any typos or drop a variable, etc. With the compiler, I added some macros, once, tweaked the compiler, once, and made some simple changes to the Lispy source code, and the change was done.

It was also very easy to do things like discover basic things like what rules depended on what variables, or what variables were simply not in the spec. That was all done interactively at the listener by simply querying the data structures that were created and writing a few simple functions.

The other fella working on his own rules had less to do and took longer and was much more resistant to changes than I was, and for good reason. I described to the client that I was collecting all of the requirements and specifications into a large cloud of Stuff and any time they asked, the cloud would rain down and create a solid structure. But, while in the cloud, anything can easily be changed. So, while I was keeping the specs in an etheral state, the other fella had to chisel his into stone by using the straight RSL code. The later into the project, the more solid his structure and more difficult any changes were.

I even had time to optimize some of the rules. There were several rules like IF a AND b then MESSAGE X, ELSE IF a AND c THEN MESSAGE Y. Only the rules had several common variables. I was able to capture those rules just as specified, with the redundant conditions, and had the compiler simplify the expression to get the common ones factored out.

Finally, I didn’t “ask permission” to do this, I simply did it. I didn’t go to my boss, or the client and say “Hey, I want to use Lisp here”. The task was “convert this spreadsheet into RSL”. THEY wanted the RSL Source Code for the rules, and that’s what my tool created for them. About a week into the task, my boss wanted some status, and by that time I already had all of the rules keyed into my format, had the basic structure down, and was moving ahead. He’s not a Lisp Guy, and tends to fear tools, but I assured him I was ahead of schedule, that changes were easy, and should I ever starting falling behind, I was always able to “snap shot” all of the Lispy stuff into pure RSL and go from there, not losing any time in the process.

I think the idea of being able to easily drop back into “conventional mode” was a reassurance. If all else failed, I could always go back to doing it the Hard Way. But, certainly there are cultural issues involved and every place is different.

It’s biggest problem, in the end, was that it used too many parentheses in the generated code, and tended to run long IF statements together on a single line. I didn’t put the time into writing a prettier code generator, although it was nice and indented, and looked really good. It was even spitting out comments for what rules were being implemented in which parts.

But, the real nice part was that later, when I wasn’t doing any more work on it, they took all of the generated RSL and reorganized it as RSL. It probably took the guy more than a week to do what I would have done in 30 minutes, but it showed that the RSL code was viable, useable and readable.

I couldn’t have done this without Lisp simply because I would have had to work on grammars, parsers, lexers, and crap like that. I relied on the reader and macros to make my “language”. I was never behind (save at one point when my generated RSL was too big for Java, it has an implicit class size limit), and I took every change they threw at me. I was able to do simple data manipulations and queries using the listener, I never had a more sophisticated interface than simply a text editor. No GUI, no nothing.

Overall, it was a complete Lisp hack. Relying on lots of global structures, I was constantly zapping all of the data, and reloading things, but it was never slow enough to matter. It was also totally evolutionary. No plan, just baby steps each way. When I found that I was way ahead I was able to put time into the optimizers and such, and I had the capacity to absorb the changes that they were throwing at me.

Obviously not every application falls into the mold. This was something that had a nice, regular structure, and the RSL was easy to compile code into. Also, being a code generator, it’s not practical in environments where others do NOT have the tools, and who will end up working on the generated code rather than the abstract meta language. When they tore my generated code apart for a later version, there was no going back to my original meta code. Also, I was fortunate to be the only one on the task, meaning I didn’t have to write the tool for others to use, which would have been a severe time sink.

It was also really important in that it gave ideas on how we can possibly redirect how the content is created in the future. If the clinicians can create those spreadsheet specs that they sent me, then they are really close to being able to create something just a little more regular and be able to create the clinical content directly, whether with S-Expr or with a new grammar and language.

The key is, though, that a lot of this went under the radar. It was a “results over process” success. If your group is focused more on process than results, then there’s not much you can do. But the other thing is that it was nice to bring Lisp into the everyday work world for what I was doing. While people create little scripts all day long, they never seem to think that they can do the same in Lisp, and leverage them even better later on.

Also, one last thing, this was my first major attack of something in Lisp. The first time I really used Lisp “in anger”. I didn’t leverage years of Lisp experience to pull this off, just years of sitting around here on c.l.l. and occasionally dabbling a little. I relied mostly on the Hyperspec to figure things out.

It was great fun to do, because I had all of the rules keyed in. So, whenever the next stage in the compiler was finished there was lots of code generated. Whenever a change was made, it was nice to get the change, say, “Hang on”, and a minute later say “All done!”, with that minute consumed by making the change and regenerating the code. The best feature of the tool was the confidence it gave me that the changes were correct, knowing that changing A to B was all that was necessary. With large code bases, simple changes can be very simple, but they don’t need to get too complex before you start doubting and questioning whether you had caught everything.

In the end, the Lisp code was about 1800 lines. The rule code was about 8000 lines, and it generated a boat load of RSL. It was great to see how the changing of a single variable in one of the rules changed an RSL file from 1700 lines to 2500 lines, and that alone showed how important this process was to saving my sanity.


Will Hartung (wi…