**Want to start a startup?** Get funded by [Y
Combinator](http://ycombinator.com/apply.html).  
  
  
May 2002  
  
"We were after the C++ programmers. We managed to drag a lot of them about
halfway to Lisp."  
  
\- Guy Steele, co-author of the Java spec  
  
  
In the software business there is an ongoing struggle between the pointy-
headed academics, and another equally formidable force, the pointy-haired
bosses. Everyone knows who the pointy-haired boss is, right? I think most
people in the technology world not only recognize this cartoon character, but
know the actual person in their company that he is modelled upon.  
  
The pointy-haired boss miraculously combines two qualities that are common by
themselves, but rarely seen together: (a) he knows nothing whatsoever about
technology, and (b) he has very strong opinions about it.  
  
Suppose, for example, you need to write a piece of software. The pointy-haired
boss has no idea how this software has to work, and can't tell one programming
language from another, and yet he knows what language you should write it in.
Exactly. He thinks you should write it in Java.  
  
Why does he think this? Let's take a look inside the brain of the pointy-
haired boss. What he's thinking is something like this. Java is a standard. I
know it must be, because I read about it in the press all the time. Since it
is a standard, I won't get in trouble for using it. And that also means there
will always be lots of Java programmers, so if the programmers working for me
now quit, as programmers working for me mysteriously always do, I can easily
replace them.  
  
Well, this doesn't sound that unreasonable. But it's all based on one unspoken
assumption, and that assumption turns out to be false. The pointy-haired boss
believes that all programming languages are pretty much equivalent. If that
were true, he would be right on target. If languages are all equivalent, sure,
use whatever language everyone else is using.  
  
But all languages are not equivalent, and I think I can prove this to you
without even getting into the differences between them. If you asked the
pointy-haired boss in 1992 what language software should be written in, he
would have answered with as little hesitation as he does today. Software
should be written in C++. But if languages are all equivalent, why should the
pointy-haired boss's opinion ever change? In fact, why should the developers
of Java have even bothered to create a new language?  
  
Presumably, if you create a new language, it's because you think it's better
in some way than what people already had. And in fact, Gosling makes it clear
in the first Java white paper that Java was designed to fix some problems with
C++. So there you have it: languages are not all equivalent. If you follow the
trail through the pointy-haired boss's brain to Java and then back through
Java's history to its origins, you end up holding an idea that contradicts the
assumption you started with.  
  
So, who's right? James Gosling, or the pointy-haired boss? Not surprisingly,
Gosling is right. Some languages _are_ better, for certain problems, than
others. And you know, that raises some interesting questions. Java was
designed to be better, for certain problems, than C++. What problems? When is
Java better and when is C++? Are there situations where other languages are
better than either of them?  
  
Once you start considering this question, you have opened a real can of worms.
If the pointy-haired boss had to think about the problem in its full
complexity, it would make his brain explode. As long as he considers all
languages equivalent, all he has to do is choose the one that seems to have
the most momentum, and since that is more a question of fashion than
technology, even he can probably get the right answer. But if languages vary,
he suddenly has to solve two simultaneous equations, trying to find an optimal
balance between two things he knows nothing about: the relative suitability of
the twenty or so leading languages for the problem he needs to solve, and the
odds of finding programmers, libraries, etc. for each. If that's what's on the
other side of the door, it is no surprise that the pointy-haired boss doesn't
want to open it.  
  
The disadvantage of believing that all programming languages are equivalent is
that it's not true. But the advantage is that it makes your life a lot
simpler. And I think that's the main reason the idea is so widespread. It is a
_comfortable_ idea.  
  
We know that Java must be pretty good, because it is the cool, new programming
language. Or is it? If you look at the world of programming languages from a
distance, it looks like Java is the latest thing. (From far enough away, all
you can see is the large, flashing billboard paid for by Sun.) But if you look
at this world up close, you find that there are degrees of coolness. Within
the hacker subculture, there is another language called Perl that is
considered a lot cooler than Java. Slashdot, for example, is generated by
Perl. I don't think you would find those guys using Java Server Pages. But
there is another, newer language, called Python, whose users tend to look down
on Perl, and [more](accgen.html) waiting in the wings.  
  
If you look at these languages in order, Java, Perl, Python, you notice an
interesting pattern. At least, you notice this pattern if you are a Lisp
hacker. Each one is progressively more like Lisp. Python copies even features
that many Lisp hackers consider to be mistakes. You could translate simple
Lisp programs into Python line for line. It's 2002, and programming languages
have almost caught up with 1958.  
  
**Catching Up with Math**  
  
What I mean is that Lisp was first discovered by John McCarthy in 1958, and
popular programming languages are only now catching up with the ideas he
developed then.  
  
Now, how could that be true? Isn't computer technology something that changes
very rapidly? I mean, in 1958, computers were refrigerator-sized behemoths
with the processing power of a wristwatch. How could any technology that old
even be relevant, let alone superior to the latest developments?  
  
I'll tell you how. It's because Lisp was not really designed to be a
programming language, at least not in the sense we mean today. What we mean by
a programming language is something we use to tell a computer what to do.
McCarthy did eventually intend to develop a programming language in this
sense, but the Lisp that we actually ended up with was based on something
separate that he did as a [theoretical exercise](rootsoflisp.html)\-- an
effort to define a more convenient alternative to the Turing Machine. As
McCarthy said later,

> Another way to show that Lisp was neater than Turing machines was to write a
> universal Lisp function and show that it is briefer and more comprehensible
> than the description of a universal Turing machine. This was the Lisp
> function
> [_eval_](https://sep.turbifycdn.com/ty/cdn/paulgraham/jmc.lisp?t=1688221954&)...,
> which computes the value of a Lisp expression.... Writing _eval_ required
> inventing a notation representing Lisp functions as Lisp data, and such a
> notation was devised for the purposes of the paper with no thought that it
> would be used to express Lisp programs in practice.

What happened next was that, some time in late 1958, Steve Russell, one of
McCarthy's grad students, looked at this definition of _eval_ and realized
that if he translated it into machine language, the result would be a Lisp
interpreter.  
  
This was a big surprise at the time. Here is what McCarthy said about it later
in an interview:

> Steve Russell said, look, why don't I program this _eval_..., and I said to
> him, ho, ho, you're confusing theory with practice, this _eval_ is intended
> for reading, not for computing. But he went ahead and did it. That is, he
> compiled the _eval_ in my paper into [IBM] 704 machine code, fixing bugs,
> and then advertised this as a Lisp interpreter, which it certainly was. So
> at that point Lisp had essentially the form that it has today....

Suddenly, in a matter of weeks I think, McCarthy found his theoretical
exercise transformed into an actual programming language-- and a more powerful
one than he had intended.  
  
So the short explanation of why this 1950s language is not obsolete is that it
was not technology but math, and math doesn't get stale. The right thing to
compare Lisp to is not 1950s hardware, but, say, the Quicksort algorithm,
which was discovered in 1960 and is still the fastest general-purpose sort.  
  
There is one other language still surviving from the 1950s, Fortran, and it
represents the opposite approach to language design. Lisp was a piece of
theory that unexpectedly got turned into a programming language. Fortran was
developed intentionally as a programming language, but what we would now
consider a very low-level one.  
  
[Fortran I](history.html), the language that was developed in 1956, was a very
different animal from present-day Fortran. Fortran I was pretty much assembly
language with math. In some ways it was less powerful than more recent
assembly languages; there were no subroutines, for example, only branches.
Present-day Fortran is now arguably closer to Lisp than to Fortran I.  
  
Lisp and Fortran were the trunks of two separate evolutionary trees, one
rooted in math and one rooted in machine architecture. These two trees have
been converging ever since. Lisp started out powerful, and over the next
twenty years got fast. So-called mainstream languages started out fast, and
over the next forty years gradually got more powerful, until now the most
advanced of them are fairly close to Lisp. Close, but they are still missing a
few things....  
  
**What Made Lisp Different**  
  
When it was first developed, Lisp embodied nine new ideas. Some of these we
now take for granted, others are only seen in more advanced languages, and two
are still unique to Lisp. The nine ideas are, in order of their adoption by
the mainstream,

  1. Conditionals. A conditional is an if-then-else construct. We take these for granted now, but Fortran I didn't have them. It had only a conditional goto closely based on the underlying machine instruction.  
  

  2. A function type. In Lisp, functions are a data type just like integers or strings. They have a literal representation, can be stored in variables, can be passed as arguments, and so on.  
  

  3. Recursion. Lisp was the first programming language to support it.  
  

  4. Dynamic typing. In Lisp, all variables are effectively pointers. Values are what have types, not variables, and assigning or binding variables means copying pointers, not what they point to.  
  

  5. Garbage-collection.  
  

  6. Programs composed of expressions. Lisp programs are trees of expressions, each of which returns a value. This is in contrast to Fortran and most succeeding languages, which distinguish between expressions and statements.  
  
It was natural to have this distinction in Fortran I because you could not
nest statements. And so while you needed expressions for math to work, there
was no point in making anything else return a value, because there could not
be anything waiting for it.  
  
This limitation went away with the arrival of block-structured languages, but
by then it was too late. The distinction between expressions and statements
was entrenched. It spread from Fortran into Algol and then to both their
descendants.  
  

  7. A symbol type. Symbols are effectively pointers to strings stored in a hash table. So you can test equality by comparing a pointer, instead of comparing each character.  
  

  8. A notation for code using trees of symbols and constants.  
  

  9. The whole language there all the time. There is no real distinction between read-time, compile-time, and runtime. You can compile or run code while reading, read or run code while compiling, and read or compile code at runtime.  
  
Running code at read-time lets users reprogram Lisp's syntax; running code at
compile-time is the basis of macros; compiling at runtime is the basis of
Lisp's use as an extension language in programs like Emacs; and reading at
runtime enables programs to communicate using s-expressions, an idea recently
reinvented as XML.

When Lisp first appeared, these ideas were far removed from ordinary
programming practice, which was dictated largely by the hardware available in
the late 1950s. Over time, the default language, embodied in a succession of
popular languages, has gradually evolved toward Lisp. Ideas 1-5 are now
widespread. Number 6 is starting to appear in the mainstream. Python has a
form of 7, though there doesn't seem to be any syntax for it.  
  
As for number 8, this may be the most interesting of the lot. Ideas 8 and 9
only became part of Lisp by accident, because Steve Russell implemented
something McCarthy had never intended to be implemented. And yet these ideas
turn out to be responsible for both Lisp's strange appearance and its most
distinctive features. Lisp looks strange not so much because it has a strange
syntax as because it has no syntax; you express programs directly in the parse
trees that get built behind the scenes when other languages are parsed, and
these trees are made of lists, which are Lisp data structures.  
  
Expressing the language in its own data structures turns out to be a very
powerful feature. Ideas 8 and 9 together mean that you can write programs that
write programs. That may sound like a bizarre idea, but it's an everyday thing
in Lisp. The most common way to do it is with something called a _macro._  
  
The term "macro" does not mean in Lisp what it means in other languages. A
Lisp macro can be anything from an abbreviation to a compiler for a new
language. If you want to really understand Lisp, or just expand your
programming horizons, I would [learn more](onlisp.html) about macros.  
  
Macros (in the Lisp sense) are still, as far as I know, unique to Lisp. This
is partly because in order to have macros you probably have to make your
language look as strange as Lisp. It may also be because if you do add that
final increment of power, you can no longer claim to have invented a new
language, but only a new dialect of Lisp.  
  
I mention this mostly as a joke, but it is quite true. If you define a
language that has car, cdr, cons, quote, cond, atom, eq, and a notation for
functions expressed as lists, then you can build all the rest of Lisp out of
it. That is in fact the defining quality of Lisp: it was in order to make this
so that McCarthy gave Lisp the shape it has.  
  
**Where Languages Matter**  
  
So suppose Lisp does represent a kind of limit that mainstream languages are
approaching asymptotically-- does that mean you should actually use it to
write software? How much do you lose by using a less powerful language? Isn't
it wiser, sometimes, not to be at the very edge of innovation? And isn't
popularity to some extent its own justification? Isn't the pointy-haired boss
right, for example, to want to use a language for which he can easily hire
programmers?  
  
There are, of course, projects where the choice of programming language
doesn't matter much. As a rule, the more demanding the application, the more
leverage you get from using a powerful language. But plenty of projects are
not demanding at all. Most programming probably consists of writing little
glue programs, and for little glue programs you can use any language that
you're already familiar with and that has good libraries for whatever you need
to do. If you just need to feed data from one Windows app to another, sure,
use Visual Basic.  
  
You can write little glue programs in Lisp too (I use it as a desktop
calculator), but the biggest win for languages like Lisp is at the other end
of the spectrum, where you need to write sophisticated programs to solve hard
problems in the face of fierce competition. A good example is the [airline
fare search program](carl.html) that ITA Software licenses to Orbitz. These
guys entered a market already dominated by two big, entrenched competitors,
Travelocity and Expedia, and seem to have just humiliated them
technologically.  
  
The core of ITA's application is a 200,000 line Common Lisp program that
searches many orders of magnitude more possibilities than their competitors,
who apparently are still using mainframe-era programming techniques. (Though
ITA is also in a sense using a mainframe-era programming language.) I have
never seen any of ITA's code, but according to one of their top hackers they
use a lot of macros, and I am not surprised to hear it.  
  
**Centripetal Forces**  
  
I'm not saying there is no cost to using uncommon technologies. The pointy-
haired boss is not completely mistaken to worry about this. But because he
doesn't understand the risks, he tends to magnify them.  
  
I can think of three problems that could arise from using less common
languages. Your programs might not work well with programs written in other
languages. You might have fewer libraries at your disposal. And you might have
trouble hiring programmers.  
  
How much of a problem is each of these? The importance of the first varies
depending on whether you have control over the whole system. If you're writing
software that has to run on a remote user's machine on top of a buggy, closed
operating system (I mention no names), there may be advantages to writing your
application in the same language as the OS. But if you control the whole
system and have the source code of all the parts, as ITA presumably does, you
can use whatever languages you want. If any incompatibility arises, you can
fix it yourself.  
  
In server-based applications you can get away with using the most advanced
technologies, and I think this is the main cause of what Jonathan Erickson
calls the "[programming language
renaissance](http://www.byte.com/documents/s=1821/byt20011214s0003/)." This is
why we even hear about new languages like Perl and Python. We're not hearing
about these languages because people are using them to write Windows apps, but
because people are using them on servers. And as software shifts [off the
desktop](road.html) and onto servers (a future even Microsoft seems resigned
to), there will be less and less pressure to use middle-of-the-road
technologies.  
  
As for libraries, their importance also depends on the application. For less
demanding problems, the availability of libraries can outweigh the intrinsic
power of the language. Where is the breakeven point? Hard to say exactly, but
wherever it is, it is short of anything you'd be likely to call an
application. If a company considers itself to be in the software business, and
they're writing an application that will be one of their products, then it
will probably involve several hackers and take at least six months to write.
In a project of that size, powerful languages probably start to outweigh the
convenience of pre-existing libraries.  
  
The third worry of the pointy-haired boss, the difficulty of hiring
programmers, I think is a red herring. How many hackers do you need to hire,
after all? Surely by now we all know that software is best developed by teams
of less than ten people. And you shouldn't have trouble hiring hackers on that
scale for any language anyone has ever heard of. If you can't find ten Lisp
hackers, then your company is probably based in the wrong city for developing
software.  
  
In fact, choosing a more powerful language probably decreases the size of the
team you need, because (a) if you use a more powerful language you probably
won't need as many hackers, and (b) hackers who work in more advanced
languages are likely to be smarter.  
  
I'm not saying that you won't get a lot of pressure to use what are perceived
as "standard" technologies. At Viaweb (now Yahoo Store), we raised some
eyebrows among VCs and potential acquirers by using Lisp. But we also raised
eyebrows by using generic Intel boxes as servers instead of "industrial
strength" servers like Suns, for using a then-obscure open-source Unix variant
called FreeBSD instead of a real commercial OS like Windows NT, for ignoring a
supposed e-commerce standard called
[SET](http://news.com.com/2100-1017-225723.html) that no one now even
remembers, and so on.  
  
You can't let the suits make technical decisions for you. Did it alarm some
potential acquirers that we used Lisp? Some, slightly, but if we hadn't used
Lisp, we wouldn't have been able to write the software that made them want to
buy us. What seemed like an anomaly to them was in fact cause and effect.  
  
If you start a startup, don't design your product to please VCs or potential
acquirers. _Design your product to please the users._ If you win the users,
everything else will follow. And if you don't, no one will care how
comfortingly orthodox your technology choices were.  
  
**The Cost of Being Average**  
  
How much do you lose by using a less powerful language? There is actually some
data out there about that.  
  
The most convenient measure of power is probably [code size](power.html). The
point of high-level languages is to give you bigger abstractions-- bigger
bricks, as it were, so you don't need as many to build a wall of a given size.
So the more powerful the language, the shorter the program (not simply in
characters, of course, but in distinct elements).  
  
How does a more powerful language enable you to write shorter programs? One
technique you can use, if the language will let you, is something called
[bottom-up programming](progbot.html). Instead of simply writing your
application in the base language, you build on top of the base language a
language for writing programs like yours, then write your program in it. The
combined code can be much shorter than if you had written your whole program
in the base language-- indeed, this is how most compression algorithms work. A
bottom-up program should be easier to modify as well, because in many cases
the language layer won't have to change at all.  
  
Code size is important, because the time it takes to write a program depends
mostly on its length. If your program would be three times as long in another
language, it will take three times as long to write-- and you can't get around
this by hiring more people, because beyond a certain size new hires are
actually a net lose. Fred Brooks described this phenomenon in his famous book
_The Mythical Man-Month,_ and everything I've seen has tended to confirm what
he said.  
  
So how much shorter are your programs if you write them in Lisp? Most of the
numbers I've heard for Lisp versus C, for example, have been around 7-10x. But
a recent article about ITA in [_New
Architect_](http://www.newarchitectmag.com/documents/s=2286/new1015626014044/)
magazine said that "one line of Lisp can replace 20 lines of C," and since
this article was full of quotes from ITA's president, I assume they got this
number from ITA. If so then we can put some faith in it; ITA's software
includes a lot of C and C++ as well as Lisp, so they are speaking from
experience.  
  
My guess is that these multiples aren't even constant. I think they increase
when you face harder problems and also when you have smarter programmers. A
really good hacker can squeeze more out of better tools.  
  
As one data point on the curve, at any rate, if you were to compete with ITA
and chose to write your software in C, they would be able to develop software
twenty times faster than you. If you spent a year on a new feature, they'd be
able to duplicate it in less than three weeks. Whereas if they spent just
three months developing something new, it would be _five years_ before you had
it too.  
  
And you know what? That's the best-case scenario. When you talk about code-
size ratios, you're implicitly assuming that you can actually write the
program in the weaker language. But in fact there are limits on what
programmers can do. If you're trying to solve a hard problem with a language
that's too low-level, you reach a point where there is just too much to keep
in your head at once.  
  
So when I say it would take ITA's imaginary competitor five years to duplicate
something ITA could write in Lisp in three months, I mean five years if
nothing goes wrong. In fact, the way things work in most companies, any
development project that would take five years is likely never to get finished
at all.  
  
I admit this is an extreme case. ITA's hackers seem to be unusually smart, and
C is a pretty low-level language. But in a competitive market, even a
differential of two or three to one would be enough to guarantee that you'd
always be behind.  
  
**A Recipe**  
  
This is the kind of possibility that the pointy-haired boss doesn't even want
to think about. And so most of them don't. Because, you know, when it comes
down to it, the pointy-haired boss doesn't mind if his company gets their ass
kicked, so long as no one can prove it's his fault. The safest plan for him
personally is to stick close to the center of the herd.  
  
Within large organizations, the phrase used to describe this approach is
"industry best practice." Its purpose is to shield the pointy-haired boss from
responsibility: if he chooses something that is "industry best practice," and
the company loses, he can't be blamed. He didn't choose, the industry did.  
  
I believe this term was originally used to describe accounting methods and so
on. What it means, roughly, is _don't do anything weird._ And in accounting
that's probably a good idea. The terms "cutting-edge" and "accounting" do not
sound good together. But when you import this criterion into decisions about
technology, you start to get the wrong answers.  
  
Technology often _should_ be cutting-edge. In programming languages, as Erann
Gat has pointed out, what "industry best practice" actually gets you is not
the best, but merely the average. When a decision causes you to develop
software at a fraction of the rate of more aggressive competitors, "best
practice" is a misnomer.  
  
So here we have two pieces of information that I think are very valuable. In
fact, I know it from my own experience. Number 1, languages vary in power.
Number 2, most managers deliberately ignore this. Between them, these two
facts are literally a recipe for making money. ITA is an example of this
recipe in action. If you want to win in a software business, just take on the
hardest problem you can find, use the most powerful language you can get, and
wait for your competitors' pointy-haired bosses to revert to the mean.  
  

* * *

  
  
  
  
**Appendix: Power**  
  
As an illustration of what I mean about the relative power of programming
languages, consider the following problem. We want to write a function that
generates accumulators-- a function that takes a number n, and returns a
function that takes another number i and returns n incremented by i.  
  
(That's _incremented by_ , not plus. An accumulator has to accumulate.)  
  
In Common Lisp this would be  (defun foo (n) (lambda (i) (incf n i)))  and in
Perl 5,  sub foo { my ($n) = @_; sub {$n += shift} }  which has more elements
than the Lisp version because you have to extract parameters manually in Perl.  
  
In Smalltalk the code is slightly longer than in Lisp  foo: n |s| s := n.
^[:i| s := s+i. ]  because although in general lexical variables work, you
can't do an assignment to a parameter, so you have to create a new variable s.  
  
In Javascript the example is, again, slightly longer, because Javascript
retains the distinction between statements and expressions, so you need
explicit `return` statements to return values:  function foo(n) { return
function (i) { return n += i } }  (To be fair, Perl also retains this
distinction, but deals with it in typical Perl fashion by letting you omit
`return`s.)  
  
If you try to translate the Lisp/Perl/Smalltalk/Javascript code into Python
you run into some limitations. Because Python doesn't fully support lexical
variables, you have to create a data structure to hold the value of n. And
although Python does have a function data type, there is no literal
representation for one (unless the body is only a single expression) so you
need to create a named function to return. This is what you end up with:  def
foo(n): s = [n] def bar(i): s[0] += i return s[0] return bar  Python users
might legitimately ask why they can't just write  def foo(n): return lambda i:
return n += i  or even  def foo(n): lambda i: n += i  and my guess is that
they probably will, one day. (But if they don't want to wait for Python to
evolve the rest of the way into Lisp, they could always just...)  
  
In OO languages, you can, to a limited extent, simulate a closure (a function
that refers to variables defined in enclosing scopes) by defining a class with
one method and a field to replace each variable from an enclosing scope. This
makes the programmer do the kind of code analysis that would be done by the
compiler in a language with full support for lexical scope, and it won't work
if more than one function refers to the same variable, but it is enough in
simple cases like this.  
  
Python experts seem to agree that this is the preferred way to solve the
problem in Python, writing either  def foo(n): class acc: def __init__(self,
s): self.s = s def inc(self, i): self.s += i return self.s return acc(n).inc
or  class foo: def __init__(self, n): self.n = n def __call__(self, i): self.n
+= i return self.n  I include these because I wouldn't want Python advocates
to say I was misrepresenting the language, but both seem to me more complex
than the first version. You're doing the same thing, setting up a separate
place to hold the accumulator; it's just a field in an object instead of the
head of a list. And the use of these special, reserved field names, especially
`__call__`, seems a bit of a hack.  
  
In the rivalry between Perl and Python, the claim of the Python hackers seems
to be that that Python is a more elegant alternative to Perl, but what this
case shows is that power is the ultimate elegance: the Perl program is simpler
(has fewer elements), even if the syntax is a bit uglier.  
  
How about other languages? In the other languages mentioned in this talk--
Fortran, C, C++, Java, and Visual Basic-- it is not clear whether you can
actually solve this problem. Ken Anderson says that the following code is
about as close as you can get in Java:  public interface Inttoint { public int
call(int i); }  public static Inttoint foo(final int n) { return new
Inttoint() { int s = n; public int call(int i) { s = s + i; return s; }}; }
This falls short of the spec because it only works for integers. After many
email exchanges with Java hackers, I would say that writing a properly
polymorphic version that behaves like the preceding examples is somewhere
between damned awkward and impossible. If anyone wants to write one I'd be
very curious to see it, but I personally have timed out.  
  
It's not literally true that you can't solve this problem in other languages,
of course. The fact that all these languages are Turing-equivalent means that,
strictly speaking, you can write any program in any of them. So how would you
do it? In the limit case, by writing a Lisp interpreter in the less powerful
language.  
  
That sounds like a joke, but it happens so often to varying degrees in large
programming projects that there is a name for the phenomenon, Greenspun's
Tenth Rule:

> Any sufficiently complicated C or Fortran program contains an ad hoc
> informally-specified bug-ridden slow implementation of half of Common Lisp.

If you try to solve a hard problem, the question is not whether you will use a
powerful enough language, but whether you will (a) use a powerful language,
(b) write a de facto interpreter for one, or (c) yourself become a human
compiler for one. We see this already begining to happen in the Python
example, where we are in effect simulating the code that a compiler would
generate to implement a lexical variable.  
  
This practice is not only common, but institutionalized. For example, in the
OO world you hear a good deal about "patterns". I wonder if these patterns are
not sometimes evidence of case (c), the human compiler, at work. When I see
patterns in my programs, I consider it a sign of trouble. The shape of a
program should reflect only the problem it needs to solve. Any other
regularity in the code is a sign, to me at least, that I'm using abstractions
that aren't powerful enough-- often that I'm generating by hand the expansions
of some macro that I need to write.  
  
  
  
**Notes**  
  

  * The IBM 704 CPU was about the size of a refrigerator, but a lot heavier. The CPU weighed 3150 pounds, and the 4K of RAM was in a separate box weighing another 4000 pounds. The Sub-Zero 690, one of the largest household refrigerators, weighs 656 pounds.  
  

  * Steve Russell also wrote the first (digital) computer game, Spacewar, in 1962.  
  

  * If you want to trick a pointy-haired boss into letting you write software in Lisp, you could try telling him it's XML.  
  

  * Here is the accumulator generator in other Lisp dialects:  Scheme: (define (foo n) (lambda (i) (set! n (+ n i)) n)) Goo: (df foo (n) (op incf n _))) Arc: (def foo (n) [++ n _]) 
  * Erann Gat's sad tale about "industry best practice" at JPL inspired me to address this generally misapplied phrase.  
  

  * Peter Norvig found that 16 of the 23 patterns in _Design Patterns_ were "[invisible or simpler](http://www.norvig.com/design-patterns/)" in Lisp.  
  

  * Thanks to the many people who answered my questions about various languages and/or read drafts of this, including Ken Anderson, Trevor Blackwell, Erann Gat, Dan Giffin, Sarah Harlin, Jeremy Hylton, Robert Morris, Peter Norvig, Guy Steele, and Anton van Straaten. They bear no blame for any opinions expressed.  
  

  
  
**Related:**  
  
Many people have responded to this talk, so I have set up an additional page
to deal with the issues they have raised: [Re: Revenge of the
Nerds](icadmore.html).  
  
It also set off an extensive and often useful discussion on the
[LL1](http://www.ai.mit.edu/~gregs/ll1-discuss-archive-html/threads.html)
mailing list. See particularly the mail by Anton van Straaten on semantic
compression.  
  
Some of the mail on LL1 led me to try to go deeper into the subject of
language power in [Succinctness is Power](power.html).  
  
A larger set of canonical implementations of the [accumulator generator
benchmark](accgen.html) are collected together on their own page.  
  
[Japanese
Translation](http://www.shiro.dreamhost.com/scheme/trans/icad-j.html),
[Spanish
Translation](http://kapcoweb.com/p/docs/translations/revenge_of_the_nerds/revenge_of_the_nerds-
es.html), [Chinese
Translation](http://flyingapplet.spaces.live.com/blog/cns!F682AFBD82F7E261!375.entry
)  
  

