Lisp Hackers: Luke Gorrie [+ his ECLM video]

Luke Gorrie is a proverbial hacker following his passion for programming to various places in the physical world, like Sweden or Nepal, or programming world, like Erlang, Forth, Lisp, Lua, or some other fringe language. And enjoying the process of exploration and meeting different people, while fiddling with computers, from OLPC to telecom equipment, working with world-famous technologists, including Joe Armstrong or Alan Kay, and, generally, doing whatever he likes in the programming world.

He was one of the main authors of SLIME in its early days. And recently he founded a Lisp networking startup Teclo Networks, the story of which (as of fall of 2011) he told at ECLM 2011. Here's the video, that he asked to hold off for some time due to business reasons, and only now it's posted online. Enjoy!

Luke's twitter account is @lukego

Tell us something interesting about yourself.

I enjoy exploring the world. I was born and raised in Australia (Brisbane), I've lived for many years in Sweden and become a Swedish citizen, and these days I'm extremely happy to be settling myself into Switzerland. I've spent a couple of years traveling continuously with just my backpack and unicycle and no home anywhere to go back to. I've found this interesting. You can find links to my exploits on my homepage.

I like to feel a bit out of my depth and to be "the new guy" who has a lot of catching up to do. This is why I so much enjoy learning new programming languages and visiting new programming communities so much: the feeling of having to think really hard about how to formulate even the most basic programs, just like when I was a kid, while other people do it so naturally.

What's your job? Tell us about your company.

I'm currently starting a new project called Snabb. It's too early to say very much about this yet, so I'll talk about the past.

I've had a few major jobs that have shaped my thinking. I worked in each one for about 3-5 years.

The first was Bluetail AB, the first Erlang startup company. I was hired by Joe Armstrong because I had enthusiasm pouring out of my ears and nostrils. I moved immediately to Stockholm in the middle of winter for this job -- I was 21 years old and I'd never left Australia or seen snow before. I learned a lot of things at Bluetail, besides practical matters like how to walk on ice. The programmers there were all way above my level and I was routinely stunned at the stuff they had done, like when Tobbe Törnqvist mentioned in passing that he'd written his own TCP/IP stack from scratch as a hobby project and that his dial-up internet connection uses his own home-brew PPP implementation. I used to roam the corridors at night borrowing tech books from people's shelves, there must have been a thousand books in the office.

Bluetail was bought by Alteon, who were bought by Nortel at the same time, and become a productive little product unit in a big networking company.

Next was Synapse Mobile Networks. This was an amazing experience for me: to switch from a big company to a small company and take care of everything from design to development to deployment to support by ourselves. Really getting to know customers and internalizing their needs and building the right solutions. The product is a device management system, which is a realtime database in a mobile phone network keeping track of which phone everybody is using and making sure all their services work. The whole thing was written in Erlang and BerkeleyDB, even with a from-scratch SS7 telecom networking stack in the end. I would routinely fly to a really interesting country -- Kazakhstan, Jordan, Russia, Algeria, you name it -- and spend a few weeks deploying the system and developing customizations on-site. Synapse was the first company in this market and they are still the market leader today. The system has by now configured approximately 1 billion actual mobile phones by sending them coded SMSes.

Synapse was also instructive in seeing how much a strong personality can shape a company. I'm still in awe of our fearless leader Per Bergqvist. What a guy, as they say on Red Dwarf.

The most recent is Teclo Networks. This is a company that I co-founded with friends from the SBCL community -- mostly drinking buddies from ECLM -- and friends from the telecom world. I served as CTO during the phase of finding the right problem to solve, building our series of prototypes and our real product, and finding our very first customers. I'm a Teclo-alumnus now, not actively working in the company, and: Wow, this was a really intense few years.

Teclo builds network appliances that optimize TCP traffic for cellular internet at about 20Gbps per server. The product speeds up the network, improves consistency, and globally eliminates buffer-bloat. The company is currently moving forward with a lot of momentum: we have Lispers like Juho Snellman, Tobias Rittweiler, and Ties Stuij currently deploying systems in real live networks all over the world. Go Teclo :-)

Do you use Lisp at work? If yes, how you've made it happen? If not, why?

I've mostly done Lisp hacking for my own pleasure on the side, but I've also used it quite a bit at work.

The first time was when I used Scheme at Bluetail. Specifically, I used Kawa to extend a Java application. I'm sure this raised some eyebrows amongst my colleagues but frankly I was having too much fun to really notice. Kawa is a great piece of software.

I wrote a bunch of Common Lisp networking code while reading books like TCP/IP Illustrated. This was a hobby project called Slitch and Netkit. I used this slightly in my work at Nortel to replicate a DoS against the Linux kernel that was crashing some of our appliances.

Teclo is very much a Lisp-hacker shop. In the first year or so we used Lisp for absolutely everything. We've written and deployed a prototype TCP/IP implementation written in Common Lisp (SBCL), wrote network analysis tools for cross-referencing and visualizing traffic captures (often working on traces that fill up a whole disk i.e. hundreds of gigabytes), and developed all of the operation-and-maintenance infrastructure in CL. These days Teclo uses C/C++ for the main traffic handling, R for statistical analysis, and Common Lisp for the rest -- mostly operation and maintenance and data visualization.

Among software projects you've participated in what's your favorite?

SLIME! This was wild fun. The project started when Eric Marsden, a CMUCL hacker, posted to #lisp his weekend hack to annotate individual S-expressions in an Emacs buffer with CMUCL compiler messages. His source files were slim.el and skank.lisp, after the Fatboy Slim song he was listening to at the time. I loved the idea so I started toying with it, renaming the files to slime.el and swank.lisp to make them easy to diff. I quickly posted my version to the cmucl-dev mailing list where Helmut Eller jumped right into it too. We created a Sourceforge project and quickly snowballed from there to over 100 contributors.

SLIME's mission was ultimately to replace ILISP as the standard Emacs mode for interacting with Common Lisp. ILISP worked by sending S-expressions between Emacs and Lisp via standard I/O and it had the unfortunate habit of getting stuck a lot. ILISP was also about 15 years old at that time (SLIME is catching up now at 8 years!) and really hard to work on due to the heavy use of reader conditionals in the source code, like #+cmucl #-lucid #+sbcl #-lispworks #+acl #-acl4.2 and so on.

I really enjoyed the feeling of working on a growing and thriving open-source project. Seeing the steady stream of new names appearing on our mailing list, getting patches from dozens of people, feeling good about positive feedback we received, working hard on negative feedback right away, and so on. Twas a really productive flow.

I think that writing development tools is also really satisfying because your users are your peer group: people you really look up to and respect and sometimes drink beer with. It's a great feeling to build stuff that they like to use.

Helmut Eller and I also had a really great working style. Very often I'd do some late-night hacking and check in a bunch of new functionality, which Helmut would then read through and think about and then thoughtfully rewrite in a simpler way. Then I'd see what he'd done, think about it, and rewrite it to be simpler again. And so on. This was a really pleasant and productive way of working. He is also an absolute magician when it comes to suddenly checking in what seems like a month worth of work that he did over the weekend. (Juho Snellman has this uncanny ability too.)

I hacked on SLIME from the beginning and up to version 1.0. Then I was engulfed by an Erlang startup. Here're some posts that I fished out of the mailing list archives to give a sense of the early days:

What brought you to Lisp? What holds you?

My friend Darius Bacon brought me to Lisp (Scheme) by gently and persistently singing the praises of Abelson & Sussman back in the days when I was a teenager hacking Java. This book was a revelation for me: particularly the Digital Circuit Simulator. So I was a Scheme-lover for several years, but Darius also gently and persistently sang the praises of Norvig's Paradigms of AI Programming, which was another revelation to me, and made a Common Lisp convert of me.

What holds me to Lisp is the people. I love hanging out with Lisp hackers: I find that we're an unusually diverse community. How often do you attend a small conference where attendees are building nuclear defense systems, running intensive care wards, designing aeroplane engines, analysing Lute tablature, developing cancer drugs, writing FIFA's legal contracts, and designing their own microchips? Surely this describes few tech events other than Arthur & Edi's European Common Lisp Meeting :-).

What you dislike the most about Lisp?

I have a few stock rants that I'm tempted to rattle off -- fragmentation, threads, GC-phobia -- but honestly I doubt they are applicable these days. There have been so many improvements to SBCL and great developments like Quicklisp and so on.

I can say I'm personally disappointed about the missed opportunity for us to write Teclo's production traffic path in SBCL. Ultimately, the software has just a few microseconds' budget to process each packet, and can never spike latency by more than a millisecond. I don't know how to deliver that kind of performance in a high-level language like Lisp. So we fell back to C.

I'd also like to have embedded SBCL in the C program to take care of high-level work like slurping in configurations and spitting out statistics. But the SBCL runtime system is a bit heavyweight to make that practical. It gets in the way when you want to debug with strace, gdb, etc. So we wrote this stuff in C++ instead.

I'd have written a lot more Lisp code in recent years if I'd found good solutions to those problems. But at the end of the day it is C's niche to write lots of tiny state machines with extremely predictable performance characteristics, so I'm not especially shocked or disheartened. A language can't occupy every niche at once :-).

Describe your workflow, give some productivity tips to fellow programmers

I'm an incrementalist. I like to start from minimal running code, like (defun program () (print "Program 0.1")), and move forward in a long series of very small steps. I tend to choose designs that I know are too simple or too slow, because I enjoy the feeling of hitting their limits and knowing that I didn't prematurely generalize or optimize them. Then I fix them. I'd say that I'm much influenced by watching the development of Extreme Programming on WardsWiki in the 90s.

This isn't a hard and fast rule though. In Teclo I once spent a whole month writing a complex program without even trying to compile it once. This was a rewrite of the main traffic engine in C after having written a prototype in Lisp previously. This was a really fun way to work actually. I produced a tremendous amount of bugs in this style though and I wasn't smart enough to fix them. Christophe Rhodes did that part -- don't ask me how :-).

I do have a tip for getting into "the flow". It's a simple one: make a little TODO list of some features you want to hack, and take the laptop into the park away from the internet for an hour or two until they're done. This works every time for me.

Oh, and I highly recommend printing out and reading your programs. This is the best way that I know for improving their quality. This is why I'm a bit picky about things like the 80-column rule and the layout of functions within a file. I want to be able to print programs out and read them on paper from top to bottom. I wrote a program called pbook to help with this -- it's not a very good implementation though, with all those regexps, so I'd love if someone would make a much simpler one.

You have played around with so many languages, like Erlang, Lisp, Smalltalk & Lua. If you would design your own, how would it look like?

That's really hard to imagine. I'd have to find a reason that I needed a new programming language, and the details would probably follow from the problem I needed to solve.

I learn new languages mostly because I enjoy meeting new people and learning new ways of thinking. It's very seldom from any sense of dissatisfaction with previous languages I've used. My favourite languages are Common Lisp, Emacs Lisp, Forth, Erlang, Smalltalk, and C. So the best I can say is: those are the languages that I'd like to have designed.

P.S. Luke asked to give my warm thanks to John Q. Splittist for reading over these answers before I sent them to you (and for many other things!).

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