Immutability offers significant benefits for software design, even in resource-constrained embedded systems. The post explores practical techniques including using C's `const` keyword for pseudo-immutability, separating old and new state in update functions (new_state = f(old_state, other_data)), and how this mirrors how microprocessor registers actually work at the hardware level. It covers immutable (persistent) data structures like cons-cell lists, the tradeoffs of recursion vs. iteration, tail call optimization, and message-passing as a concurrency alternative to shared mutable state with locks. The key limitation for embedded systems is that fully persistent data structures require dynamic memory allocation and garbage collection, making them impractical in most low-level C environments. The pseudo-immutable pattern — decoupling state computation from state mutation — is presented as a pragmatic middle ground that reduces bugs and improves code clarity.
