Author: Tord Romstad
Date: 02:21:33 02/18/04
Go up one level in this thread
Hi Vincent,
Some comments and explanations below:
On February 17, 2004 at 19:33:52, Vincent Diepeveen wrote:
>Let's start the functional programming subject.
Why? Lisp is not a functional programming language, although it allows
you to write programs in a functional style if you want. Functional
programming is not the only, nor even the most common style of programming
in Common Lisp.
>Have you ever written a serious application in LISP?
Yes. I worked three years as a full-time Lisp programmer in Telenor,
the leading Norwegian telecom company. This was huge, multi-layered
and multi-threaded server applications central to all Telenor's activities
as an Internet service provider. The applications were used, directly
or indirectly, by about one million Norwegian customers every day, in
addition to lots of employees in Telenor. Briefly explained, the main
tasks of the applications were to administrate Telenor's databases of
customers, accounts, products and services, automatically distribute all
changes in user configuration to those systems which needed to be aware
of them, real-time rating of Internet connections and all other
volum-based Internet services (as well as mobile phone calls and some
other non-Internet-related volume-based stuff), as well as billing the
customers.
Because of the application's central importance in Telenor and the
huge number of simultaneous users, performance and stability were
extremely important. 100% uptime was a very important requirement.
Hence the ability to modify and upgrade the programs while they were
running was essential.
Concerning your problems with the syntax:
The syntax is fully programmable. Common Lisp readtables are
first-class objects, and can be copied, manipulated and hacked any
way you want. Common Lisp is a language construction kit just as
much as a language. The reason why the default syntax looks the
way it is is that keeping the base syntax as simple and fluid as
possible makes it easier to build new languages on top of it. It
is easy (trivial, in fact) for a Lisp program to write Lisp code,
precisely because of the syntax.
As I have tried to explain (probably in a clumsy way) elsewhere in
the thread, the most common way to write big and complicated programs
in Lisp is to build a domain-specific language on top of Lisp, and
write the final program in this language. This language does not
need to resemble Lisp at all.
>((((((((((a b c)(a))))))(((())))))(((())))
>
>Sentences like above are not so easy to understand. C is way easier.
But the line of Lisp "code" above doesn't do anything. It isn't code
at all in any meaningful sense of the word. I would even claim that
you would never even see anything like the above line in a Lisp program,
unless it is written by an incompetent Lisper or it is deliberately
obfuscated.
But you are right that one of the strengths of Lisp, which it shares
with C, is that it allows you to write incredibly obfuscated code if
you want to.
As a curiosity which some people may find amusing (at least I did
the first time I saw it), I provide the following bilingual program
(the first line in the program should be blank):
t(setq /*;*/){}main(){char q='\"',s='\\';char*a=
"~%t(setq /*;*/){}main(){char q='~A';char*a=
~S;char*b=/*
)(setq a ~S)
(setq */ ~S;printf(b,s,q,s,s,q,a,q,q,s,s,s,q,s,s,s,s,q,q,b,q/*
)(format t /* a /* a */);}~%";char*b=/*
)(setq a "\\\"',s='\\\\")
(setq */ "
t(setq /*;*/){}main(){char q='%c%c',s='%c%c';char*a=
%c%s%c;char*b=/*
)(setq a %c%c%c%c%c',s='%c%c%c%c%c)
(setq */ %c%s%c;printf(b,s,q,s,s,q,a,q,q,s,s,s,q,s,s,s,s,q,q,b,q/*
)(format t /* a /* a */);}
";printf(b,s,q,s,s,q,a,q,q,s,s,s,q,s,s,s,s,q,q,b,q/*
)(format t /* a /* a */);}
Believe it or not, this program compiles in C as well as Lisp, and
has precisely the same effect in both languages: It prints out its
own source code (in other words, it is what is usually called a
Quine).
>AFAIK only some grey old emacs fans write their stuff in LISP.
Emacs Lisp is an old, ugly and inefficient Lisp dialect, and doesn't
really belong in this discussion.
>When i define something in LISP there i continuesly make (((()))((()))
>mistakes.
I suppose it happens that I misplace a paren too when writing Lisp, but
it happens no more often than that I forget a semicolon when writing C.
And when I do misplace a paren, at least the error is easy to fix: I
just press C-M-q, and it is immediately obvious exactly where the error
is.
But of course, you need a Lisp-aware editor in order to write and edit
Lisp code efficiently.
Tord
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