[llimos]

The 'previous' feature sounds like a great idea! The compiler could even decide which variables it needs to keep track of.

[squeaky-clean]

I think it would lead to a lot of hard to find logical bugs in a lot of projects but I think it would be a great operator in say, a scripting language for a turn based game.

[marssaxman]

I am currently working on a DSL which actually does include a "back" operator! The language is used to describe simulated circuits, so you can inquire about the value a register had during a previous clock cycle.