"The quantity of meaning compressed into a small space by
algebraic signs, is another circumstance that facilitates
the reasonings we are accustomed to carry on by their aid."|
- Charles Babbage, quoted in Iverson's Turing Award Lecture
In the discussion about issues raised by Revenge
of the Nerds on the LL1 mailing list, Paul Prescod wrote
something that stuck in my mind.
Python's goal is regularity and readability, not succinctness.
On the face of it, this seems a rather damning thing to claim about a
programming language. As far as I can tell, succinctness = power.
If so, then substituting, we get
Python's goal is regularity and readability, not power.
and this doesn't seem a tradeoff (if it is a tradeoff)
that you'd want to make.
It's not far from saying that Python's goal is not to be effective
as a programming language.
Does succinctness = power? This seems to me an important question,
maybe the most important question for anyone interested in
language design, and one that it would be useful to confront
directly. I don't feel sure yet that the answer is a simple yes, but it seems
a good hypothesis to begin with.
My hypothesis is that succinctness is power, or is close enough
that except in pathological examples you can treat them as
It seems to me that succinctness is what programming languages are
for. Computers would be just as happy to be told what to
do directly in machine language. I think that the main
reason we take the trouble to develop high-level languages is to
get leverage, so that we can say (and more importantly, think)
in 10 lines of a high-level language what would require 1000
lines of machine language. In other words,
the main point of high-level languages is to make source code smaller.
If smaller source code is the purpose of high-level languages, and
the power of something is how well it achieves its purpose, then
the measure of the power of a programming language is how small it
makes your programs.
Conversely, a language that doesn't make your programs small is
doing a bad job of what programming languages are supposed to
do, like a knife that doesn't cut well, or printing that's illegible.
Small in what sense though? The most common measure of code size is
lines of code. But I think that this metric is the most common because
it is the easiest to measure. I don't think anyone really believes
it is the true test of the length of a program. Different
languages have different conventions for how much you should put
on a line; in C a lot of lines have nothing on them but a delimiter or two.
Another easy test is the number of characters in a
program, but this is not very good either; some languages (Perl,
for example) just
use shorter identifiers than others.
I think a better measure of the size of a program would be the
number of elements, where an element is anything that
would be a distinct node if you drew a tree representing the
source code. The name of
a variable or function is an element;
an integer or a floating-point number is an element;
a segment of literal text is an element;
an element of a pattern, or a format directive, is an element;
a new block is an element. There are borderline cases
(is -5 two elements or one?) but I think most of them are the
same for every language, so they don't affect comparisons much.
This metric needs fleshing out, and
it could require interpretation in the case of specific languages,
but I think it tries to measure the right thing, which is the
number of parts a program has. I think the tree you'd draw in this
exercise is what you have to make in your head in order to
conceive of the program, and so its size is proportionate to the
amount of work you have to do to write or read it.
This kind of metric would allow us to compare different languages,
but that is not, at least for me, its main value. The main value
of the succinctness test is as a guide in designing languages.
The most useful comparison between languages is between two
potential variants of the same language. What can I do in the
language to make programs shorter?
If the conceptual load of
a program is proportionate to its complexity, and a given programmer
can tolerate a fixed conceptual load, then this is the same as asking,
what can I do to enable programmers to get the most done? And
that seems to me identical to asking, how can I design a good
(Incidentally, nothing makes it more patently obvious that the old
chestnut "all languages are equivalent" is false than designing
languages. When you are designing a new language, you're constantly
comparing two languages-- the language if I did x, and if I didn't-- to
decide which is better. If this were really a meaningless question,
you might as well flip a coin.)
Aiming for succinctness seems a good way to find new ideas.
If you can do something that makes many
different programs shorter, it is probably not a coincidence: you have
probably discovered a useful new abstraction. You might even be
able to write a program to help by searching
source code for repeated patterns. Among other languages, those
with a reputation for succinctness would be the ones to look to for
new ideas: Forth, Joy, Icon.
The first person to write about these issues, as far as I know, was
Fred Brooks in the Mythical Man Month. He wrote
that programmers seemed to generate about the same
amount of code per day regardless of the language.
When I first read this in my early twenties,
it was a big surprise to me and seemed to have huge implications.
It meant that (a) the only way to get software written faster was to
use a more succinct language, and (b) someone who took the
trouble to do this could leave competitors who didn't in the dust.
Brooks' hypothesis, if it's true, seems to be at the very heart of hacking.
In the years since, I've paid close attention to any evidence I could
get on the question, from formal studies to anecdotes about individual
projects. I have seen nothing to contradict him.
I have not yet seen evidence that seemed to me conclusive,
and I don't expect to. Studies
like Lutz Prechelt's comparison of programming languages, while
generating the kind of results I expected, tend to use problems that
are too short to be meaningful tests. A better test of a language is
what happens in programs that take a month to write. And the only
real test, if you believe as I do that the main purpose of a language
is to be good to think in (rather than just to tell a computer what to
do once you've thought of it) is what new things you can write in it.
So any language comparison where
you have to meet a predefined spec is testing slightly the wrong
The true test of a language is how well you can discover
and solve new problems, not
how well you can use it to solve a problem someone else has
already formulated. These two are quite different criteria.
In art, mediums like embroidery and mosaic work well if you
know beforehand what you want to make, but are absolutely lousy if
you don't. When you want to discover the image as you make it--
as you have to do with anything as complex as an image of a
person, for example-- you need to use a more fluid medium like pencil or
ink wash or oil paint. And indeed, the way tapestries and mosaics are made in
practice is to make a painting first, then copy it. (The word
"cartoon" was originally used to describe a painting intended for
What this means is that we are never likely to have accurate comparisons
of the relative power of programming languages. We'll have precise
comparisons, but not accurate ones. In particular, explicit studies
for the purpose of comparing languages,
because they will probably use small problems, and will necessarily use
predefined problems, will tend to underestimate the power of the
more powerful languages.
Reports from the field, though they will necessarily be less precise than
"scientific" studies, are likely to be more meaningful. For example,
Ulf Wiger of Ericsson did a
concluded that Erlang was 4-10x
more succinct than C++, and proportionately faster to develop
Comparisons between Ericsson-internal development projects indicate
similar line/hour productivity, including all phases of software development,
rather independently of which language (Erlang, PLEX, C, C++, or Java)
was used. What differentiates the different languages then becomes source
The study also deals explictly with a point that was
only implicit in Brooks' book (since he measured lines of debugged code):
programs written in more powerful languages tend to have fewer bugs.
That becomes an end in itself, possibly more important than programmer
productivity, in applications like network switches.
The Taste Test
Ultimately, I think you have to go with your gut. What does it feel
like to program in the language? I think the way to find (or design)
the best language is to become hypersensitive to how well a language
lets you think, then choose/design the language that feels best. If
some language feature is awkward or restricting, don't worry, you'll
know about it.
Such hypersensitivity will come at a cost. You'll find that you can't
stand programming in clumsy languages. I find it unbearably
restrictive to program in languages without macros, just as someone used
to dynamic typing finds it unbearably restrictive to have to go back to
programming in a language where you have to declare the type of
every variable, and can't make a list of objects of different types.
I'm not the only one. I know many Lisp hackers that this has happened
to. In fact, the most accurate measure of the relative power of programming
languages might be the percentage of people who know the language
who will take any job where they get to use that language, regardless
of the application domain.
I think most hackers know what it means for a language to feel restrictive.
What's happening when you feel that? I think it's the same feeling
you get when the street you want to take is blocked off, and you have to
take a long detour to get where you wanted to go. There is something
you want to say, and the language won't let you.
What's really going on here, I think, is that a restrictive language is
one that isn't succinct enough. The problem is not simply that you can't
say what you planned to. It's that the detour the language makes you
take is longer. Try this thought experiment. Suppose there were
some program you wanted to write, and the language wouldn't let you
express it the way you planned to, but instead forced you to write the
program in some other way that was shorter. For me at least,
that wouldn't feel very restrictive. It would be like the street you
wanted to take being blocked off, and the policeman at the
intersection directing you to a shortcut instead of a detour. Great!
I think most (ninety percent?) of
the feeling of restrictiveness comes from being forced to make the program
you write in the language longer than one you have in your head.
Restrictiveness is mostly lack of succinctness.
So when a language feels restrictive, what that (mostly) means is that it isn't
succinct enough, and when a language isn't succinct, it will
The quote I began with mentions two other qualities, regularity and
readability. I'm not sure what regularity is, or what advantage,
if any, code that is regular and readable has over code that is merely
readable. But I think I know what is meant by readability, and I think
it is also related to succinctness.
We have to be careful here to distinguish between the readability of
an individual line of code and the readability of the whole program.
It's the second that matters. I agree that a line of Basic is likely to be
more readable than a line of Lisp. But a program written in Basic is
is going to have more lines than the same program written in
Lisp (especially once you cross over into Greenspunland). The
total effort of reading the Basic program will surely be greater.
total effort = effort per line x number of lines
I'm not as sure that readability is directly proportionate to succinctness
as I am that power is, but certainly succinctness is a factor
(in the mathematical sense; see equation above) in readability.
So it may not even be meaningful to say that the goal of a language is
readability, not succinctness; it could be like saying the goal was readability,
What readability-per-line does mean, to the user encountering the language
for the first time, is that source code will look unthreatening. So
could be a good marketing decision, even if it is a bad design
decision. It's isomorphic to the very successful technique of letting
people pay in installments: instead of frightening them with a high
upfront price, you tell them the low monthly payment. Installment plans
are a net lose for the buyer, though, as mere readability-per-line probably
is for the programmer.
The buyer is going to make a lot of those low, low payments; and
the programmer is going to read a lot of those individually readable lines.
This tradeoff predates programming languages. If you're used to reading
novels and newspaper articles, your first experience of reading a math
paper can be dismaying. It could take half an hour to read a single page.
And yet, I am pretty sure that the notation is not the problem, even though
it may feel like it is. The math paper is hard to read
because the ideas are hard. If you expressed the same ideas in prose
(as mathematicians had to do before they evolved succinct notations),
they wouldn't be any easier to read, because the paper would grow to the
size of a book.
To What Extent?
A number of people have rejected
the idea that succinctness = power. I think it would be more useful, instead
of simply arguing that they are the same or aren't, to ask:
to what extent does succinctness = power?
Because clearly succinctness is
a large part of what higher-level languages are for. If it is not all they're
for, then what else are they for, and how important, relatively, are these
I'm not proposing this just to make the debate more civilized. I really
want to know the answer. When, if ever, is a language too succinct for
its own good?
The hypothesis I began with was that, except in pathological examples,
I thought succinctness could be considered identical with power. What
I meant was that in any language anyone would design, they
would be identical, but that if someone wanted to design a language
explicitly to disprove this hyphothesis, they could probably do it. I'm
not even sure of that, actually.
Languages, not Programs
We should be clear that we are talking about the succinctness
of languages, not of individual programs.
It certainly is possible for individual programs to be written too densely.
I wrote about this in On Lisp. A complex macro
may have to save many times its own length to be justified. If writing
some hairy macro could save you ten lines of code every time you use it,
and the macro is itself ten lines of code, then you get a net saving in
lines if you use it more than twice. But that could still be a bad move,
because macro definitions are harder to read than ordinary code. You
might have to use the macro ten or twenty times before it yielded a net
improvement in readability.
I'm sure every language has such tradeoffs (though I suspect the stakes
get higher as the language gets more powerful). Every programmer must
have seen code that some clever person has made marginally shorter
by using dubious programming tricks.
So there is no argument about that-- at least, not from me. Individual
programs can certainly be too succinct for their own good. The question
is, can a language be? Can a language compel programmers to write
code that's short (in elements) at the expense of overall readability?
One reason it's hard to imagine a language being too succinct is that if
there were some excessively compact way to phrase something, there would
probably also be a longer way. For example, if you felt Lisp programs using
a lot of macros or higher-order functions were too dense, you could, if you
preferred, write code that was isomorphic to Pascal. If you
don't want to express factorial in Arc as a call to a higher-order function
(rec zero 1 * 1-)
you can also write out a recursive definition:
(rfn fact (x) (if (zero x) 1 (* x (fact (1- x)))))
Though I can't off the top of my head think of any examples, I am interested
in the question of whether a language could be too succinct. Are there languages
that force you to write code in a way that is crabbed and incomprehensible?
If anyone has examples, I would be very interested to see them.
(Reminder: What I'm looking for are programs that are very dense according
to the metric of "elements" sketched above, not merely programs that are
short because delimiters can be omitted and everything has a one-character name.)