[rini17]

Common Lisp solves the big structure problem using "setf" form. It also generally has both destructive/inplace and nondestructive structure manipulation versions of practically all functions in standard library.

It solves parent-child problem by having symbols as built-in data type. They can be used exactly as the "mutable mediator" describes. And beyond, such as you can generate a code that uses these symbols and have it natively compiled - at runtime.