April 2001, rev. April 2003
(This article is derived from a talk given at the 2001 Franz
It describes how we used Lisp to write Viaweb Store, which
is still, as Yahoo! Store, the most popular e-commerce
software, running about 20,000 stores.)
In the summer of 1995, my friend Robert Morris and I
started a startup called Viaweb. Our plan was to write
software that would let end users build online stores.
What was novel about this software, at the time, was
that it ran on our server, using ordinary Web pages
as the interface.
A lot of people could have been having this idea at the
same time, of course, but as far as I know, Viaweb was
the first Web-based application. It seemed such
a novel idea to us that we named the company after it:
Viaweb, because our software worked via the Web,
instead of running on your desktop computer.
Another unusual thing about this software was that it
was written primarily in a programming language called
Lisp. It was one of the first big end-user
applications to be written in Lisp, which up till then
had been used mostly in universities and research labs.
Lisp gave us a
great advantage over competitors using less powerful
The Secret Weapon
Eric Raymond has written an essay called "How to Become a Hacker,"
and in it, among other things, he tells would-be hackers what
languages they should learn. He suggests starting with Python and
Java, because they are easy to learn. The serious hacker will also
want to learn C, in order to hack Unix, and Perl for system
administration and cgi scripts. Finally, the truly serious hacker
should consider learning Lisp:
Lisp is worth learning for the profound enlightenment experience
you will have when you finally get it; that experience will make
you a better programmer for the rest of your days, even if you
never actually use Lisp itself a lot.
This is the same argument you tend to hear for learning Latin. It
won't get you a job, except perhaps as a classics professor, but
it will improve your mind, and make you a better writer in languages
you do want to use, like English.
But wait a minute. This metaphor doesn't stretch that far. The
reason Latin won't get you a job is that no one speaks it. If you
write in Latin, no one can understand you. But Lisp is a computer
language, and computers speak whatever language you, the programmer,
tell them to.
So if Lisp makes you a better programmer, like he says, why wouldn't
you want to use it? If a painter were offered a brush that would
make him a better painter, it seems to me that he would want to
use it in all his paintings, wouldn't he? I'm not trying to make
fun of Eric Raymond here. On the whole, his advice is good. What
he says about Lisp is pretty much the conventional wisdom. But
there is a contradiction in the conventional wisdom: Lisp will
make you a better programmer, and yet you won't use it.
Why not? Programming languages are just tools, after all. If Lisp
really does yield better programs, you should use it. And if it
doesn't, then who needs it?
This is not just a theoretical question. Software is a very
competitive business, prone to natural monopolies. A company that
gets software written faster and better will, all other things
being equal, put its competitors out of business. And when you're
starting a startup, you feel this very keenly. Startups tend to
be an all or nothing proposition. You either get rich, or you get
nothing. In a startup, if you bet on the wrong technology, your
competitors will crush you.
Robert and I both knew Lisp well, and we couldn't see any reason
not to trust our instincts and go with Lisp. We knew that everyone
else was writing their software in C++ or Perl. But we also knew
that that didn't mean anything. If you chose technology that way,
you'd be running Windows. When you choose technology, you have to
ignore what other people are doing, and consider only what will
work the best.
This is especially true in a startup. In a big company, you can
do what all the other big companies are doing. But a startup can't
do what all the other startups do. I don't think a lot of people
realize this, even in startups.
The average big company grows at about ten percent a year. So if
you're running a big company and you do everything the way the
average big company does it, you can expect to do as well as the
average big company-- that is, to grow about ten percent a year.
The same thing will happen if you're running a startup, of course.
If you do everything the way the average startup does it, you should
expect average performance. The problem here is, average performance
means that you'll go out of business. The survival rate for startups
is way less than fifty percent. So if you're running a startup,
you had better be doing something odd. If not, you're in trouble.
Back in 1995, we knew something that I don't think our competitors
understood, and few understand even now: when you're writing
software that only has to run on your own servers, you can use
any language you want. When you're writing desktop software,
there's a strong bias toward writing applications in the same
language as the operating system. Ten years ago, writing applications
meant writing applications in C. But with Web-based software,
especially when you have the source code of both the language and
the operating system, you can use whatever language you want.
This new freedom is a double-edged sword, however. Now that you
can use any language, you have to think about which one to use.
Companies that try to pretend nothing has changed risk finding that
their competitors do not.
If you can use any language, which do you use? We chose Lisp.
For one thing, it was obvious that rapid development would be
important in this market. We were all starting from scratch, so
a company that could get new features done before its competitors
would have a big advantage. We knew Lisp was a really good language
for writing software quickly, and server-based applications magnify
the effect of rapid development, because you can release software
the minute it's done.
If other companies didn't want to use Lisp, so much the better.
It might give us a technological edge, and we needed all the help
we could get. When we started Viaweb, we had no experience in
business. We didn't know anything about marketing, or hiring
people, or raising money, or getting customers. Neither of us had
ever even had what you would call a real job. The only thing we
were good at was writing software. We hoped that would save us.
Any advantage we could get in the software department, we would
So you could say that using Lisp was an experiment. Our hypothesis
was that if we wrote our software in Lisp, we'd be able to get
features done faster than our competitors, and also to do things
in our software that they couldn't do. And because Lisp was so
high-level, we wouldn't need a big development team, so our costs
would be lower. If this were so, we could offer a better product
for less money, and still make a profit. We would end up getting
all the users, and our competitors would get none, and eventually
go out of business. That was what we hoped would happen, anyway.
What were the results of this experiment? Somewhat surprisingly,
it worked. We eventually had many competitors, on the order of
twenty to thirty of them, but none of their software could compete
with ours. We had a wysiwyg online store builder that ran on the
server and yet felt like a desktop application. Our competitors
had cgi scripts. And we were always far ahead of them in features.
Sometimes, in desperation, competitors would try to introduce
features that we didn't have. But with Lisp our development cycle
was so fast that we could sometimes duplicate a new feature within
a day or two of a competitor announcing it in a press release. By
the time journalists covering the press release got round to calling
us, we would have the new feature too.
It must have seemed to our competitors that we had some kind of
secret weapon-- that we were decoding their Enigma traffic or
something. In fact we did have a secret weapon, but it was simpler
than they realized. No one was leaking news of their features to
us. We were just able to develop software faster than anyone
When I was about nine I happened to get hold of a copy of The Day
of the Jackal, by Frederick Forsyth. The main character is an
assassin who is hired to kill the president of France. The assassin
has to get past the police to get up to an apartment that overlooks
the president's route. He walks right by them, dressed up as an
old man on crutches, and they never suspect him.
Our secret weapon was similar. We wrote our software in a weird
AI language, with a bizarre syntax full of parentheses. For years
it had annoyed me to hear Lisp described that way. But now it
worked to our advantage. In business, there is nothing more valuable
than a technical advantage your competitors don't understand. In
business, as in war, surprise is worth as much as force.
And so, I'm a little embarrassed to say, I never said anything
publicly about Lisp while we were working on Viaweb. We never
mentioned it to the press, and if you searched for Lisp on our Web
site, all you'd find were the titles of two books in my bio. This
was no accident. A startup should give its competitors as little
information as possible. If they didn't know what language our
software was written in, or didn't care, I wanted to keep it that
The people who understood our technology best were the customers.
They didn't care what language Viaweb was written in either, but
they noticed that it worked really well. It let them build great
looking online stores literally in minutes. And so, by word of
mouth mostly, we got more and more users. By the end of 1996 we
had about 70 stores online. At the end of 1997 we had 500. Six
months later, when Yahoo bought us, we had 1070 users. Today, as
Yahoo Store, this software continues to dominate its market. It's
one of the more profitable pieces of Yahoo, and the stores built
with it are the foundation of Yahoo Shopping. I left Yahoo in
1999, so I don't know exactly how many users they have now, but
the last I heard there were about 20,000.
The Blub Paradox
What's so great about Lisp? And if Lisp is so great, why doesn't
everyone use it? These sound like rhetorical questions, but actually
they have straightforward answers. Lisp is so great not because
of some magic quality visible only to devotees, but because it is
simply the most powerful language available. And the reason everyone
doesn't use it is that programming languages are not merely
technologies, but habits of mind as well, and nothing changes
slower. Of course, both these answers need explaining.
I'll begin with a shockingly controversial statement: programming
languages vary in power.
Few would dispute, at least, that high level languages are more
powerful than machine language. Most programmers today would agree
that you do not, ordinarily, want to program in machine language.
Instead, you should program in a high-level language, and have a
compiler translate it into machine language for you. This idea is
even built into the hardware now: since the 1980s, instruction sets
have been designed for compilers rather than human programmers.
Everyone knows it's a mistake to write your whole program by hand
in machine language. What's less often understood is that there
is a more general principle here: that if you have a choice of
several languages, it is, all other things being equal, a mistake
to program in anything but the most powerful one. 
There are many exceptions to this rule. If you're writing a program
that has to work very closely with a program written in a certain
language, it might be a good idea to write the new program in the
same language. If you're writing a program that only has to do
something very simple, like number crunching or bit manipulation,
you may as well use a less abstract language, especially since it
may be slightly faster. And if you're writing a short, throwaway
program, you may be better off just using whatever language has
the best library functions for the task. But in general, for
application software, you want to be using the most powerful
(reasonably efficient) language you can get, and using anything
else is a mistake, of exactly the same kind, though possibly in a
lesser degree, as programming in machine language.
You can see that machine language is very low level. But, at least
as a kind of social convention, high-level languages are often all
treated as equivalent. They're not. Technically the term "high-level
language" doesn't mean anything very definite. There's no dividing
line with machine languages on one side and all the high-level
languages on the other. Languages fall along a continuum  of
abstractness, from the most powerful all the way down to machine
languages, which themselves vary in power.
Consider Cobol. Cobol is a high-level language, in the sense that
it gets compiled into machine language. Would anyone seriously
argue that Cobol is equivalent in power to, say, Python? It's
probably closer to machine language than Python.
Or how about Perl 4? Between Perl 4 and Perl 5, lexical closures
got added to the language. Most Perl hackers would agree that Perl
5 is more powerful than Perl 4. But once you've admitted that,
you've admitted that one high level language can be more powerful
than another. And it follows inexorably that, except in special
cases, you ought to use the most powerful you can get.
This idea is rarely followed to its conclusion, though. After a
certain age, programmers rarely switch languages voluntarily.
Whatever language people happen to be used to, they tend to consider
just good enough.
Programmers get very attached to their favorite languages, and I
don't want to hurt anyone's feelings, so to explain this point I'm
going to use a hypothetical language called Blub. Blub falls right
in the middle of the abtractness continuum. It is not the most
powerful language, but it is more powerful than Cobol or machine
And in fact, our hypothetical Blub programmer wouldn't use either
of them. Of course he wouldn't program in machine language. That's
what compilers are for. And as for Cobol, he doesn't know how
anyone can get anything done with it. It doesn't even have x (Blub
feature of your choice).
As long as our hypothetical Blub programmer is looking down the
power continuum, he knows he's looking down. Languages less powerful
than Blub are obviously less powerful, because they're missing some
feature he's used to. But when our hypothetical Blub programmer
looks in the other direction, up the power continuum, he doesn't
realize he's looking up. What he sees are merely weird languages.
He probably considers them about equivalent in power to Blub, but
with all this other hairy stuff thrown in as well. Blub is good
enough for him, because he thinks in Blub.
When we switch to the point of view of a programmer using any of
the languages higher up the power continuum, however, we find that
he in turn looks down upon Blub. How can you get anything done in
Blub? It doesn't even have y.
By induction, the only programmers in a position to see all the
differences in power between the various languages are those who
understand the most powerful one. (This is probably what Eric
Raymond meant about Lisp making you a better programmer.) You can't
trust the opinions of the others, because of the Blub paradox:
they're satisfied with whatever language they happen to use, because
it dictates the way they think about programs.
I know this from my own experience, as a high school kid writing
programs in Basic. That language didn't even support recursion.
It's hard to imagine writing programs without using recursion, but
I didn't miss it at the time. I thought in Basic. And I was a
whiz at it. Master of all I surveyed.
The five languages that Eric Raymond recommends to hackers fall at
various points on the power continuum. Where they fall relative
to one another is a sensitive topic. What I will say is that I
think Lisp is at the top. And to support this claim I'll tell you
about one of the things I find missing when I look at the other
four languages. How can you get anything done in them, I think,
without macros? 
Many languages have something called a macro. But Lisp macros are
unique. And believe it or not, what they do is related to the
parentheses. The designers of Lisp didn't put all those parentheses
in the language just to be different. To the Blub programmer, Lisp
code looks weird. But those parentheses are there for a reason.
They are the outward evidence of a fundamental difference between
Lisp and other languages.
Lisp code is made out of Lisp data objects. And not in the trivial
sense that the source files contain characters, and strings are
one of the data types supported by the language. Lisp code, after
it's read by the parser, is made of data structures that you can
If you understand how compilers work, what's really going on is
not so much that Lisp has a strange syntax as that Lisp has no
syntax. You write programs in the parse trees that get generated
within the compiler when other languages are parsed. But these
parse trees are fully accessible to your programs. You can write
programs that manipulate them. In Lisp, these programs are called
macros. They are programs that write programs.
Programs that write programs? When would you ever want to do that?
Not very often, if you think in Cobol. All the time, if you think
in Lisp. It would be convenient here if I could give an example
of a powerful macro, and say there! how about that? But if I did,
it would just look like gibberish to someone who didn't know Lisp;
there isn't room here to explain everything you'd need to know to
understand what it meant. In
Ansi Common Lisp I tried to move
things along as fast as I could, and even so I didn't get to macros
until page 160.
But I think I can give a kind of argument that might be convincing.
The source code of the Viaweb editor was probably about 20-25%
macros. Macros are harder to write than ordinary Lisp functions,
and it's considered to be bad style to use them when they're not
necessary. So every macro in that code is there because it has to
be. What that means is that at least 20-25% of the code in this
program is doing things that you can't easily do in any other
language. However skeptical the Blub programmer might be about my
claims for the mysterious powers of Lisp, this ought to make him
curious. We weren't writing this code for our own amusement. We
were a tiny startup, programming as hard as we could in order to
put technical barriers between us and our competitors.
A suspicious person might begin to wonder if there was some
correlation here. A big chunk of our code was doing things that
are very hard to do in other languages. The resulting software
did things our competitors' software couldn't do. Maybe there was
some kind of connection. I encourage you to follow that thread.
There may be more to that old man hobbling along on his crutches
than meets the eye.
Aikido for Startups
But I don't expect to convince anyone (over 25) to go out and learn
Lisp. The purpose of this article is not to change anyone's mind,
but to reassure people already interested in using Lisp-- people
who know that Lisp is a powerful language, but worry because it
isn't widely used. In a competitive situation, that's an advantage.
Lisp's power is multiplied by the fact that your competitors don't
If you think of using Lisp in a startup, you shouldn't worry that
it isn't widely understood. You should hope that it stays that
way. And it's likely to. It's the nature of programming languages
to make most people satisfied with whatever they currently use.
Computer hardware changes so much faster than personal habits that
programming practice is usually ten to twenty years behind the
processor. At places like MIT they were writing programs in
high-level languages in the early 1960s, but many companies continued
to write code in machine language well into the 1980s. I bet a
lot of people continued to write machine language until the processor,
like a bartender eager to close up and go home, finally kicked them
out by switching to a risc instruction set.
Ordinarily technology changes fast. But programming languages are
different: programming languages are not just technology, but what
programmers think in. They're half technology and half religion.
And so the median language, meaning whatever language the median
programmer uses, moves as slow as an iceberg. Garbage collection,
introduced by Lisp in about 1960, is now widely considered to be
a good thing. Runtime typing, ditto, is growing in popularity.
Lexical closures, introduced by Lisp in the early 1970s, are now,
just barely, on the radar screen. Macros, introduced by Lisp in the
mid 1960s, are still terra incognita.
Obviously, the median language has enormous momentum. I'm not
proposing that you can fight this powerful force. What I'm proposing
is exactly the opposite: that, like a practitioner of Aikido, you
can use it against your opponents.
If you work for a big company, this may not be easy. You will have
a hard time convincing the pointy-haired boss to let you build
things in Lisp, when he has just read in the paper that some other
language is poised, like Ada was twenty years ago, to take over
the world. But if you work for a startup that doesn't have
pointy-haired bosses yet, you can, like we did, turn the Blub
paradox to your advantage: you can use technology that your
competitors, glued immovably to the median language, will never be
able to match.
If you ever do find yourself working for a startup, here's a handy
tip for evaluating competitors. Read their job listings. Everything
else on their site may be stock photos or the prose equivalent,
but the job listings have to be specific about what they want, or
they'll get the wrong candidates.
During the years we worked on Viaweb I read a lot of job descriptions.
A new competitor seemed to emerge out of the woodwork every month
or so. The first thing I would do, after checking to see if they
had a live online demo, was look at their job listings. After a
couple years of this I could tell which companies to worry about
and which not to. The more of an IT flavor the job descriptions
had, the less dangerous the company was. The safest kind were the
ones that wanted Oracle experience. You never had to worry about
those. You were also safe if they said they wanted C++ or Java
developers. If they wanted Perl or Python programmers, that would
be a bit frightening-- that's starting to sound like a company
where the technical side, at least, is run by real hackers. If I
had ever seen a job posting looking for Lisp hackers, I would have
been really worried.
 Viaweb at first had two parts: the editor, written in Lisp,
which people used to build their sites, and the ordering system,
written in C, which handled orders. The first version was mostly
Lisp, because the ordering system was small. Later we added two
more modules, an image generator written in C, and a back-office
manager written mostly in Perl.
In January 2003, Yahoo released a new version of the editor
written in C++ and Perl. It's hard to say whether the program is no
longer written in Lisp, though, because to translate this program
into C++ they literally had to write a Lisp interpreter: the source
files of all the page-generating templates are still, as far as I
know, Lisp code. (See Greenspun's Tenth Rule.)
 Robert Morris says that I didn't need to be secretive, because
even if our competitors had known we were using Lisp, they wouldn't
have understood why: "If they were that smart they'd already be
programming in Lisp."
 All languages are equally powerful in the sense of being Turing
equivalent, but that's not the sense of the word programmers care
about. (No one wants to program a Turing machine.) The kind of
power programmers care about may not be formally definable, but
one way to explain it would be to say that it refers to features
you could only get in the less powerful language by writing an
interpreter for the more powerful language in it. If language A
has an operator for removing spaces from strings and language B
doesn't, that probably doesn't make A more powerful, because you
can probably write a subroutine to do it in B. But if A supports,
say, recursion, and B doesn't, that's not likely to be something
you can fix by writing library functions.
 Note to nerds: or possibly a lattice, narrowing toward the top;
it's not the shape that matters here but the idea that there is at
least a partial order.
 It is a bit misleading to treat macros as a separate feature.
In practice their usefulness is greatly enhanced by other Lisp
features like lexical closures and rest parameters.
 As a result, comparisons of programming languages either take
the form of religious wars or undergraduate textbooks so determinedly
neutral that they're really works of anthropology. People who
value their peace, or want tenure, avoid the topic. But the question
is only half a religious one; there is something there worth
studying, especially if you want to design new languages.