const expected_number = 123;

const foo = fn () s32 {
    return expected_number;
}

const Error = error{
    unexpected_result,
};

const main = fn () Error!void {
    var function_pointer = foo.&;
    const result = function_pointer();
    if (result - expected_number != 0) {
        return Error.unexpected_result;
    }
}