Visitor for `Assignment` AST node.

def visit_Assignment(self, node):
        """Visitor for `Assignment` AST node."""
        obj_memory = self.memory[node.left.identifier.name]
        obj_program = self.visit(node.right)
        if obj_memory is not None:
            obj_program_value = obj_program.value
            obj_program = obj_memory
            obj_program.value = obj_program_value

        self.memory[node.left.identifier.name] = obj_program