• expression state at time t = "call_function_begin"
• Value Stack at time t = [ [ value, [ key, [ Python reference idx, [ ] ] ] ], stack ]
• the expression at time t = function call with name: "__setitem__" and arguments: [ obj, rest ]
• the element at index idx of stack (Python Object Store at time t) = Python list elements

then Value Stack at time (t + 1) = stack