Vizzy: pass-by-reference for lists

Before 0.9.507.0 Vizzy used to pass lists as reference, so we had the following behavior:

list"A"
set "B" to "A"
Change the value of "B", and "A" will change

This was changed and now a copy is passed in set X to Y and also when calling a custom instruction. There are however some legitimate use cases when an instruction/function should operate on the original list, as I explained in bug report.

After the rather unfortunate change (it broke my program) I can see 2 ways how list passing could work in Vizzy:

1. set X to Y makes a copy by default. If you want to have X reference the same list as Y then some expression (a marker) should be added to Vizzy, let's say byReference. Then we could use it:
   
   
   
   • When setting variables: set X to byReference(Y).
   
   
   • When calling custom instructions/functions: myCustomInstruction(arg1, arg2, byReference(myList1), myList2). myList1 is passed by reference and myList2 by copy.
   
   
2. Revert the bug fix so that set X to Y makes a reference. Function calls would also pass lists by reference. If you want to have a copy of your list then some new expression is needed, say copyOf. Then you could:
   
   
   
   • set variable to a copy of list: set X to copyOf(Y)
   
   
   • call a custom function/instruction: myCustomInstruction(arg1, arg2, myList1, copyOf(myList2)). As in previous point, myList1 is passed by reference and myList2 by copy.
   
   

For me the solution 2. seems more natural. It's actually the way used in many real programming languages. In Python for example we have operation like copyOf, but there is also sth like deepCopyOf which works like: when you have a list of lists, it'll make a copy of those inner lists too (recursive copy). Unlike copyOf, which should copy only the outer list, but its elements should be references to elements of the original list.