Unbound arrays

[rengolin]

Rise seems to have only bound arrays, from literals. This is fine for small test cases but it gets annoying when writing functions that take in an array of any size and try to apply a map:

%map = rise.map #rise.nat<?> #rise.array<?, !rise.float> #rise.array<?, !rise.float>

Without unbound arrays, programs will either have to generate all variants (like templates) or inline everything to make sure all unbounded dimensions are defined at code generation, neither of which are generic enough.