Worlds: Controlling the Scope of Side Effects

The state of an imperative program—e.g., the values stored in global and local variables, objects’ instance variables, and arrays—changes as its statements are executed. These changes, or side effects, are visible globally: when one part of the program modifies an object, every other part that holds a reference to the same object (either directly or indirectly) is also affected. This paper introduces worlds, a language construct that reifies the notion of program state, and enables programmers to control the scope of side effects.

This paper is from the Inventing Fundamental New Computing Technologies project at the Viewpoints Research Institute (founded by Alan Kay).

Seems like it is intended to be quite a coarse-grained approach to program state. A little like a developer checking out a copy of a project from a version control system, making changes and either committing or reverting back.

State in Clojure

Many people come to Clojure from an imperative language and find themselves out of their element when faced with Clojure's approach to doing things, while others are coming from a more functional background and assume that once they leave Clojure's functional subset, they will be faced with the same story re: state as is found in Java. This essay intends to illuminate Clojure's approach to the problems faced by imperative and functional programs in modeling the world.

From: Values and Change - Clojure's approach to Identity and State.

Farewell Marion

A brave 10 year old boy shed a tear and said goodbye to his mother at her burial site today.

Cancer claims another victim and now her husband and two boys start a new journey together.