Monday, February 11, 2008

My Road to Lisp

I, Kenny Tilton, do solemnly offer these my responses to The Road to Lisp Survey:

When did you first try Lisp seriously?

1995. My initial interest in programming when I went shopping for my first computer in 1977 was artificial intelligence so of course I heard about Lisp,and when I ran across a Lisp 1.5 Manual in some geek shop I snagged it. But I could not make any sense out of it.

Fast forward five years and now I am a VAX/VMS consultant doing business apps in tall buildings, and while reading some geek rag I am stunned to see Lisp listed as a 4GL based on the 4GL definition of being an order of magnitude more productive than a 3GL. This was strange because 4GLs generally created the illusion of greater productivity with screen builders and a super high level hence inflexible language with database stuff done for you and I knew Lisp was not like that. I filed this datapoint away and went on with my life.

Five years later I decide to write a program which could check intermediate steps of arbitrary first-year high school algebra problems as part of a math tutorial. I see Microsoft (!) offers a Logo, and I remember the 4GL datapoint and decide what the hell let's learn a new language at the same time.

I loved it and went amazingly far with Logo on the tutorial before realizing it would have to be ported to C (a most unpleasant exercise) and it was another ten years before I found my way out of the desert and back to Lisp.

Which Lisp did you try?

Common Lisp. Digitool's MCL, to be specific.

What led you to try Lisp?

I was looking for A Better Way than C for version two of my algebra tutorial. I knew I wanted OO because I could see in my C code that I was using structs in an OO kinda way. I also knew I wanted a dynamic, interactive development environment and it had to run on the Mac where I made most of my sales.

The first thing I tried was Stoney Ballard's Component Workshop, a brave attempt at a dynamic C++ which never even got to "Hello world" before Stoney gave up. Then I got Symantec C++ (I had used it when it was Michael Kahl's Think C) and freaked out when I saw incremental linking was gone and every edit-run cycle now included a twenty second link from scratch. And I was just appalled by C++ the language.

Next up was SmalltalkAgents from Quasar Knowledge Systems. QKS kept saying how great they were and how great they were going to be. Perhaps, but not by crashing my Mac every five minutes.

I then announced on Compuserve's MACDEV forum that I was giving up and was going to use C++,when a kind soul from Cambridge, Mass suggested I look at MCL. He said it was compiled, fast, mature, object-oriented and a few other things.

Well the amazing thing is that I had been skipping MCL ads in the Apple Developer association catalog for months because of my earlier experience with Logo. I had no idea of the progress in Lisp compilers.

I also had come incredibly close when I got the pre-alpha Dylan CD from Apple Computer and played with that. Dylan was being developed for Apple by Digitool and it ran atop (wait for it) Macintosh Common Lisp! Who knew?

But having read the message from Cambridge I promptly ordered a copy of MCL. It came a few days later and just while assembling the manual pages into a binder I concluded I had found The One. I gave the install CD to my two developers, told them to dump QKS, then ordered two more copies to stay honest.

The next few weeks involved everyone taking turns running to each others desk to show them neat new features we had just discovered and I have never looked back.

If you were trying Lisp out of unhappiness with another language, what was it and what did you not like about it, or what about Lisp were you hoping to find different?

I wanted a dynamic development modality, no linker especially. And an end to pointers and dereferencing and manual memory management. ie, I was looking for a better way than C and when I looked at C++ I did not find it.

How far have you gotten in your study of Lisp?

Well, it's been thirteen years, so as an application developer I am fluent.

What do you think of Lisp so far?

Perfect. Whatever it does not do, macros let me coax from CL. Being able to restart from a backtrace after hours of debugging or while trying twenty things a minute apart to get something working is an enormous win. CLOS is unspeakably powerful. A simple thing like special variables is magnificent when you really need them. Of course garbage collection is a stupendous win. The speed is crucial. Multiple inheritance and multi-methods are vital.

One thing a lot of newbies experience as did I is that when I go to find out how some function works it always turns out to work just the way I happen at that time to expect or want or need it to work. Clearly Common Lisp is the product of a long history of refinement by good engineers with a strong ethic of doing things well.

And if you have to know, Lawdy, I never want to edit without parentheses again. When reworking code the code tree is perfect for moving chunks of semantics around. And the autoindentation is a significant time saver. I refactor a lot so a lot of time in other languages goes into tediously realigning code.

No comments: