Hanging the code after unsuccessful **if:is** statement

[arakov]

Describe the bug
In the following code the program is not terminated correctly. The code works correctly till the end but the program hangs at the
end.

To Reproduce

import extensions;

class IntWrapper
{ 
    int value;
      
    constructor(int value) 
    {
       this value := value 
    }

    int cast()
       = value;  
}

class MyClass
{
    add(int n)
    {
        console.printLine("add int:(",n,")")
    }
    
    add(string s)
    {
        console.printLine("add literal:(",s,")")
    }
    
    add(o)
    {
        if (o; is int n) {
           ^ self.add(n);
        };

        console.printLine("unsupported")
    }
}

public program()
{
    var o := new MyClass();
    var wrapper := new IntWrapper(4);
    
    o.add("string");
    o.add(2);
    o.add(wrapper);
    o.add(2.3);  // when this line is commented, the code works correctly and ends without a problem
}

Expected behavior
The code must end without hanging indefinitely

[arakov]

Fixed in ELENA 6.1.2