We propose a new system-level abstraction, the lightweight immutable execution snapshot, which combines the immutable characteristics of checkpoints with the direct integration into the virtual memory subsystem of standard mutable address spaces. The abstraction can give arbitrary x86 programs and libraries system-level support for backtracking (akin to logic programming) and the ability to manipulate an entire address space as an immutable data structure (akin to functional programming). Our proposed implementation leverages modern x86 hardware-virtualization support.