I came across a thread from a few years back explaining how to use Nim on iOS, but since then it has become a requirement to target both 32-bit and 64-bit architectures. Nim generates slightly different C depending on the architecture, so I've modified the script linked there to compile both and then merge together so that Xcode can handle compiling for different architectures. I've summarised my method here with a a bare bones GitHub project as well.
I'd love to know if anyone has any suggestions for improving this at all (I'm not entirely sure if I'm handling strings crossing from Objective-C -> Nim and back in the most idiomatic way).