mike@hcradm.UUCP (Mike Tilson) (08/15/85)
Recently there has been a lot of talk about side-effects and expressions
in C. Several people have commented that a full expression language
is a good thing. Others have compared C to LISP and APL. The following
program shows what you can really do with C if you try. :-) Note that
everything is done as expression evaluation, and there are enough
parentheses to satisfy the LISP lover. :-) There are 38 lines of
actual executable code, in the form of *one* C expression which computes
a sequence of prime numbers.
(Note: an earlier version of this was submitted to the Obfuscated C
contest. I was going to let it die, but it seemed very apropos to
the recent C discussion.)
/ Michael Tilson
/ {utzoo,decvax}!hcr!hcradm!mike
=============== cut here =================
/*
* Functional programming in C. :-)
*
* Compute prime numbers using a version of the famous benchmark.
* The primes are computed multiple times, with the numbers being
* printed. Finally, the count of primes is printed and returned
* as the exit value of main.
*
* There are no semicolons in this program except for declarations
* and the one return statement. It is all done by expression
* evaluation. :-)
*
* This program has been tested on Vax UNIX System V.2. It passes lint
* with no messages, using the default options. This usage of setjmp
* conforms to the UNIX documentation, and is more powerful than
* that supported by the draft ANSI C standard.
*
* Michael Tilson
*/
/* set up the control structure, and also fool lint into being happy */
#include <setjmp.h>
jmp_buf label0, label1, label2;
int (*jump)() = (int (*)()) longjmp;
void (*label)() = (void (*)()) setjmp;
extern int printf();
void (*print)() = (void (*)()) printf;
#define TRUE 1
#define FALSE 0
#define SIZE 100
#define N 5
char flags[SIZE + 1];
main() {
int i, prime, k, count, iter;
return(
(*print)("%d iterations\n", N),
iter=1,
(((*label)(label0),iter<=N)
?(
count = 0,
i = 0,
(((*label)(label1),i<=SIZE)
? flags[i]=TRUE,
i++,
(*jump)(label1,0)
:empty()),
i = 0,
(((*label)(label1),i<=SIZE)
?(
(flags[i]
?(
prime = i+i+3,
(*print)("\n%d",prime),
k = i + prime,
(((*label)(label2),k<=SIZE)
?(
flags[k]=FALSE,
k += prime,
(*jump)(label2,0)
)
:empty()),
count++
):empty()),
i++,
(*jump)(label1,0)
):empty()),
iter++,
(*jump)(label0,0)
):empty()),
(*print)("\n%d primes.\n", count),
count
);
}
empty() {
}