//unsafe code propagation rule
rule: (X: function, Y: function)
case X call Y
    {
        warning Y tag unsafe -> X tag unsafe
        message "safe function should not call unsafe code"
    }

testfunc3 = function: (a: num, b: num)->num , unsafe //function tags list
{
	x = a+b: num;
	y = a - b: num;
	
	(x + y) / 2;
}

testfunc2 = function: (a: num)->bool // since testfunc3 marked as unsafe code,
                                             // testfunc2 should be marked so too
{
	b = testfunc3(a+1, a-1): num;
	(b==0);
}