As GoL can implement Turing Machines it is Turing complete. DDP can implement GoL, there for it is Turing complete, too.

But I also implemented a TM in DDP few years ago and just added a program (just called "x") that might or might not halt, depending of the input: https://gitlab.com/vikingosegundo/declarativeturingmachine/-/blob/main/tm/main.swift