I endorse “CHIP-2021-05 Loops: Bounded Looping Operations (bd3ebc76)” for 2026 lock-in.
In my view the Loops CHIP makes the Bitcoin Cash VM “Turing-complete within VM limits” (Linear Bounded Automaton might be the more correct term). This is very important as it greatly increases the number of useful computations that can be conveniently expressed using the VM. Together with the Functions CHIP, Loops really complete the VM. There is some overlap between these two CHIPs, but they also complement each other and should go in together.
Having implemented the Loops CHIP (in albaVm) my view is that the implementation risk is not higher than other CHIPs we have delivered recently.
Metaprogramming has been brought up as a risk (especially in the context of Functions). Loops also enable metaprogramming by making evaluators like TurtleVm more practical. Such evaluators can now be made universal and able to evaluate any size program within VM limits. And as VM limits are relaxed evaluators become more practical. Metaprogramming is evidence of the VM’s growing capability. Turing’s original machine was also capable of hosting Turing machine evaluators, with simulated tapes.
By combining Loops and our existing conditional operators it is possible to implement Functions (in an inefficient & convoluted way). One could even establish TurtleVm as such a function and call out to it from various parts of the contract without having to duplicate the evaluator at every call-site. So with Loops we can have both Functions and OP_EVAL but in an inefficient and hard to audit way. Better to establish an efficient and standard way of doing Functions (the Functions CHIP) and roll out Loops & Functions together. Also note that Loops can be expressed via the recursion provided by the Functions CHIP, but less efficiently.
With Loops and Functions the Bitcoin Cash VM becomes much more capable which opens up for more permissionless innovation. This means that we can have solutions like Quantumroot already in May 2026, instead of having to implement quantum resistance via the CHIP process.