The first thing that came to mind in terms of prior art for the immutable object type was JavaScript's Object.freeze(obj) which was released in ES 5.1 (2011):

The first thing that came to mind in terms of prior art for the immutable object type was JavaScript's Object.freeze(obj) which was released in ES 5.1 (2011): http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.8 http://www.ecma-international.org/ecma-262/5.1/#sec-15.2.3.8 Edit: replaced Object.seal with Object.freeze