I am under the impression that the current NARS200 has no external file access ability at this time. I understand that it is hard to get a good interface and get it right. However, in the meantime let me make the following proposal. It would be simple and get us a long way towards something basically useful.
Why no create a very simple C-like interface including open, close, seek, read, write, lock, unlock, etc. The read and write would do so in a binary form and support scalors, multi-dimintioanl arrays, and the like.
The last APL I used (almost 30 years ago) had this basic facility and I was able to write a full B-tree based keyed file system in APL. I used it to write several accounting systems that were used very successfully in a multi-user environment. I'm pretty sure I still have my old code around. (I even have APL utilities that allowed full nested arrays in the original APL - not APL2!)
If I am given access to the file IO I am referring to, I'd be happy to port and contribute all of my utilities.