Comment by AlotOfReading

You can. Naturals are the default because the kinds of people who write and use proof assistants think usually in terms of natural numbers first rather than the 2-adic numbers mod 2^N we use in programming, or even the plain 2-adics used for algorithmics. It's like mathematicians and 1-based indexing. It violates programming conventions, but the people using it find it easier.