The use clausel

The use clausel is a top-level definition, like a function definition for example, which provides a way to "import" code from other files (or modules). You have seen it quite a lot until now:

use Core.print

You have seen this line a lot of times and you have surely wondered what it means. But why do we call it a clausel and not a statement? In many other languages this inclusion of other code is known as the use-statement or include/import-statement, and they end with a semicolon. But, as you can see, the use clausel does not end with a semicolon in Flint, but why is that?

A statement is a line of code thats written within a scope. Many languages see the empty space in which we define our functions as their top-level scope or file-level scope. This means that global variables, imports, function definitions etc are all defined at this global scope. But Flint is a bit different in this regard. We do not call it a use-statement because in Flint there is no global scope. You cannot define a variable outside a function and use it inside multiple different functions. There is no global state in Flint, and that's a deliberate design choice. This also means that the use-clausel is not a statement, so it cannot be written inside the body of a function itself (unlike C or C++, for example).

Example

But before moving on to any more complex topics, here is a small example of creating two files and compining them together:

This is the main.ft file:

use "utils.ft"
use Core.print

def main():
    i32 x = 5;
    i32 y = 6;
    i32 res = add(x, y);
    print($"res = {res}\n");

This is the utils.ft file:

def add(i32 x, i32 y) -> i32:
    return x + y;

And you compile the program with the same command as usual:

flintc -f main.ft

When running the built program, this line will be printed to the console:

res = 11

As you can see, we have successfully called the function add defined in the file utils.ft from the main function inside the main.ft file, and the Flint compiler discovered the used file dynamically during compilation.