ZoKrates

Variables can have any name which does not start with a number. Variables are mutable, and always passed by value to functions.

Variables need to be declared to be used. Declaration and definition are always combined, so that undefined variables do not exist.

def main() {
    // declare and define `my_variable`
    field mut my_variable = 2;
    // redefine `my_variable`
    my_variable = 3;
    return;
}

Variables are immutable by default. In order to declare a mutable variable, the mut keyword is used.

def main() {
    field a = 42;
    // a = 43; <- not allowed, as `a` is immutable
    field mut b = 42;
    b = 43; // ok
    return;
}

Shadowing is allowed.

def main() -> field {
    field a = 2;
    field a = 3; // shadowing
    for u32 i in 0..5 {
        bool a = true; // shadowing
    }
    // `a` is the variable declared before the loop
    return a;
}

Functions have their own scope

def foo() -> field {
    // return myGlobal; <- not allowed
    return 42;
}

def main() -> field {
    field myGlobal = 42;
    return foo();
}

For-loops have their own scope

def main() -> u32 {
    u32 mut a = 0;
    for u32 i in 0..5 {
        a = a + i;
    }
    // return i; <- not allowed
    return a;
}