Compiler Fail?

obj6.psl

deffun counter_inc(self)
    self.x = +(self.x, 1)
in

deffun counter_dec(self)
    self.x = -(self.x, 1)
in
    
deffun make_counter(start)
    { inc: counter_inc, dec: counter_dec, x: start }
in

defvar x1 = make_counter(1) in
    defvar x2 = make_counter(2) in {
        print(x1@inc().x);
        print(x2@inc().x);
        print(x1@inc().x);
        print(x2@inc().x);
        print(x1@inc().x);
        print(x2@inc()@inc()@inc().x);
        "";
    }