Global variables

A FunC program primarily consists of function declarations/definitions and global variable declarations. This section focuses on the latter.

A global variable is declared using the global keyword, followed by the variable's type and name. For example:

global ((int, int) -> int) op;

Here's a simple program demonstrating how to use a global functional variable:

int check_assoc(int a, int b, int c) {
  return op(op(a, b), c) == op(a, op(b, c));
}

int main() {
  op = _+_;
  return check_assoc(2, 3, 9);
}

In this example, the global variable op is assigned the addition operator _+_. The program then verifies the associativity of addition using three sample integers: 2, 3, and 9.

Under the hood, global variables in FunC are stored in the c7 control register of the TVM.

In FunC, you can omit the type of global variable. In this case, the compiler determines the type based on how the variable is used. For example, you can rewrite the previous program like this:

global op;

int check_assoc(int a, int b, int c) {
  return op(op(a, b), c) == op(a, op(b, c));
}

int main() {
  op = _+_;
  return check_assoc(2, 3, 9);
}

Declaring multiple global variables

FunC allows users to declare multiple global variables using a single global keyword. The following examples are equivalent:

global int A;
global cell B;
global C;

global int A, cell B, C;

Restrictions on global and local variable names

A local variable cannot have the same name as a previously declared global variable. The following example is invalid and will not compile:

global cell C;

int main() {
  int C = 3; ;; Error: cannot declare a local variable with the same name as a global variable
  return C;
}

However, the following example is valid:

global int C;

int main() {
  int C = 3;
  return C;
}

In this case, int C = 3; is not declaring a new local variable but instead assigning value 3 to the global variable C. This behavior is explained in more detail in the section on statements.

Was this article useful?