In reply to @bubblie "The more I think": well, it really can't unless you're willing to predefine the network layout at compile time before ever reading the HDF5 file. Note that this is no different from any other compiled language (i.e. C++ ). It's just that languages like Python make this all seem "easy", because things can just be constructed on the fly at runtime. Once Nimony is stable, it _should_ (I believe) be easy enough to write a JIT compiler for Nim and then _maybe_ this can become more dynamic. (Well, there's nlvm's JIT compiler, but then you're bound to a specific LLVM version and fixed version of Nim). But this is at least a year out, if we consider the need to actually get all the related Nim packages working with Nimony (where currently the macro module is likely the biggest hurdle)