olang | O Programming Language

4.1.1 extern ¶

# file: answer.ol

extern fn u32print(number: u32): u32

fn main(): u8 {
  u32print(42)

  return 0
}

That way instead of defining the u32print function. It must be provided at the linkage step.

// file: u32print.c

#include <stdio.h>

int u32print(int number) {
  return printf("%d\n", number);
}

4.1.2 Compiling without linking ¶

If you try to compile the answer.ol file by using the olc answer.ol -o answer.o command you will receive the follow error:

/usr/bin/ld: answer.o.o: in function `main':
(.text+0x10): undefined reference to `u32print'
collect2: error: ld returned 1 exit status

That’s because O tries to link by default. To assemble the code without linking it, you can use the -c option.

olc answer.ol -c -o answer.o

After that you can do the same with the C file that contains the function that you are looking to call.

gcc u32print.c -c -o u32print.o

And then you can link both object files into an executable:

gcc answer.o u32print.o -o answer

4.1.3 Calling O from C ¶

All that is required is to set the function prototype.

# file: sum.ol

fn sum(a: u32, b: u32): u32 {
  return a + b
}

// file: csum.c

#include <stdio.h>

int sum(int a, int b);

int main() {
  printf("%d\n", sum(41, 1));
  return 0;
}

Compiling:

olc sum.ol -c -o sum.o
gcc sum.o csum.c -o csum