Vikram and I are beginning work on a native R package to interface
into X-12-arima. We have looked through gretl, and previous
discussions on kludgy interfaces involving calls to the x12a binary.
Our aim is to port as much of the functionality as possible with
native R objects, and to do away with the archaic file-based interface
of X-12-arima. Our estimate is that some X-12-arima Fortran source
will need modification as well, to separate its I/O.
We would appreciate any pointers or existing code that could help us.
If anyone is already working on something similar, we would be happy
to pool effort.