call_stack - returns information about the functions involved in calling this function
If the int argument is 0, call_stack() returns an array of the names of the on the call stack, with the first one being the most recent (i.e. the currently running program). If the int argument is 1, call_stack returns the objects in which that program is executing. If it is 2, the name of the functions are returned. If it is 3, the value of origin() in that frame is returned.