I am try to create some custom macros. How does karel pass varying number of constants into subroutines without faulting. For example: grip part (1,2). If I us argument registers in the subroutine as soon as I make it to a AR in which there is no value it will fault. How does karel do it? In grippart I can use one constant or 10, it doesn't matter. If I create my own macro I have to have the same number of AR in the subroutine as I do in the main program. Is there any way to look at an AR and if there is no value to pass through without fault?