The fibonacci.pl.c Polyglot

In computing, a polyglot is a computer program or script written in a valid form of multiple programming languages, which performs the same operations or output independent of the programming language used to compile or interpret it.

https://en.wikipedia.org/wiki/Polyglot_(computing)

The Fibonacci numbers

For fun, I programmed my own Polyglot, which is both valid Perl and C code. The exciting part about C is that \$ is a valid character to start variable names with:

#include <stdio.h>

#define \$arg function_argument
#define my int
#define sub int
#define BEGIN int main(void)

my \$arg;

sub hello() {
printf("Hello, welcome to Perl-C!\n");
printf("This program is both valid C and Perl code!\n");
printf("It calculates all fibonacci numbers from 0 to 9!\n\n");
return 0;
}

sub fibonacci() {
my \$n = \$arg;

if (\$n < 2) {
return \$n;
}

\$arg = \$n - 1;
my \$fib1 = fibonacci();
\$arg = \$n - 2;
my \$fib2 = fibonacci();

return \$fib1 + \$fib2;
}

BEGIN {
hello();
my \$i = 0;

for (\$i = 0; \$i <= 10; ++\$i) {
\$arg = \$i;
printf("fib(%d) = %d\n", \$i, fibonacci());
}

return 0;
}

You can find the full source code at GitHub:

https://codeberg.org/snonux/perl-c-fibonacci

Let's run it with Perl:

❯ perl fibonacci.pl.c
Hello, welcome to Perl-C!
This program is both valid C and Perl code!
It calculates all fibonacci numbers from 0 to 9!

fib(0) = 0
fib(1) = 1
fib(2) = 1
fib(3) = 2
fib(4) = 3
fib(5) = 5
fib(6) = 8
fib(7) = 13
fib(8) = 21
fib(9) = 34
fib(10) = 55

Let's compile it as C and run the binary:

❯ gcc fibonacci.pl.c -o fibonacci
❯ ./fibonacci
Hello, welcome to Perl-C!
This program is both valid C and Perl code!
It calculates all fibonacci numbers from 0 to 9!

fib(0) = 0
fib(1) = 1
fib(2) = 1
fib(3) = 2
fib(4) = 3
fib(5) = 5
fib(6) = 8
fib(7) = 13
fib(8) = 21
fib(9) = 34
fib(10) = 55

It's entertaining to play with :-).