Codes and lists of codes are both common Prolog data structures. Create internal representations which optimize for this use case. These representations will occupy less memory (the bottleneck in most benchmarks).

Make a Code type which implements the Number interface. It should just be a rune under the hood. The current implementation for integers requires a pointer to a struct which wraps a bool and a slice. A Code type would also be helpful for representing small integers, which are very common in real world code.

Make a CodeList which implements the Callable interface. It should just be a []rune under the hood. Unification with other list terms returns a slice where possible. The current implementation for code lists requires a linked list of terms which adds substantial memory overhead.